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    experts and does not necessarily represent the decisions or the stated
    policy of the United Nations Environment Programme, the International
    Labour Organisation, or the World Health Organization.

    Published under the joint sponsorship of
    the United Nations Environment Programme,
    the International Labour Organisation,
    and the World Health Organization

    World Health Orgnization
    Geneva, 1987

         The International Programme on Chemical Safety (IPCS) is a
    joint venture of the United Nations Environment Programme, the
    International Labour Organisation, and the World Health
    Organization. The main objective of the IPCS is to carry out and
    disseminate evaluations of the effects of chemicals on human health
    and the quality of the environment. Supporting activities include
    the development of epidemiological, experimental laboratory, and
    risk-assessment methods that could produce internationally
    comparable results, and the development of manpower in the field of
    toxicology. Other activities carried out by the IPCS include the
    development of know-how for coping with chemical accidents,
    coordination of laboratory testing and epidemiological studies, and
    promotion of research on the mechanisms of the biological action of

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1. SUMMARY     




    4.1. General background     
    4.2. Recognition of the index cases     
    4.3. Screening of populations for suspected cases   
    4.4. Case definition    
    4.5. Case identification    
    4.6. Importance of pathological studies     
    4.7. Reporting systems and case records     


    5.1. General background     
    5.2. Collection of information and criteria for obtaining 
    5.3. In-depth study of cases    
    5.4. Evaluation of epidemiological data     


    6.1. Experimental animal studies    
    6.2. Analysis for toxic substances  
    6.3. Toxic chemical information data systems    


    7.1. Causation in human disease     
    7.2. Consideration of a chemical etiology   
    7.3. Temporal relationships     
    7.4. Biological plausibility    
    7.5. Dose-response and dose-effect relationships    
    7.6. Effects of intervention    
    7.7. Confirmation of a causal relationship  


    8.1. Preventive action and control  
    8.2. Surveillance and monitoring system     
    8.3. Health education   


    9.1. Cooperation and collaboration among countries  
    9.2. Global and regional activities     
    9.3. Final recommendations  




               ON KASHIN-BECK DISEASE   



a,c     Professor L. Amin-Zaki, Former Professor of Paediatrics
           (Baghdad), Abu Dhabi, United Arab Emirates

a       Professor E.A. Bababunmi, Laboratory of Biomembrane
           Research, Department of Biochemistry, University of
           Ibadan, College of Medicine, Ibadan, Nigeria

a       Dr R.V. Bhat, National Institute of Nutrition, Indian
           Council of Medical Research, Hyderabad, India

a,b,d   Dr J. Borgoño, University of Chile, Department of
           International Affairs, Ministry of Health, Santiago,
           Chile  (Vice-Chairman)

a       Dr Y. Egashira, National Institute of Health, Hatano
           Research Institute, Food and Drug Research Centre,
           Hatanoshi, Kanagawa-ken, Japan

a,b,d   Dr R.A. Goyer, National Institute of Environmental
           Health Sciences, Research Triangle Park, North
           Carolina, USA

a,c,d   Dr P. Grandjean, Institute of Community Health,
           Department of Environmental Medicine, Odense
           University, Odense, Denmark

a       Dr V.N. Ivanov, Chita Medical Institute, Chita, USSR

a       Dr V.V. Ivanov, Department of Pathophysiology,
           Krasnoyarsk Medical Institute, Krasnoyarsk, USSR

a,b,e   Dr R.D. Kimbrough, Center for Environmental Health,
           Centers for Disease Control, Atlanta, Georgia, USA

a,d     Professor P. Krogh, Department of Microbiology, Royal
           Dental College, Copenhagen, Denmark  (Rapporteur)

a,c     Dr O.A. Levander, Vitamin and Mineral Nutrition
           Laboratory, Human Nutrition Research Center, US
           Department of Agriculture, Beltsville, Maryland, USA

a,c     Dr K.R. Mahaffey, Division of Standards Development
           and Technology Transfer, National Institute for
           Occupational Safety and Health, Cincinnati, Ohio, USA 

a,d     Dr G. Martin-Bouyer, Ministère de la Santé, Direction
           Générale de la Santé, Paris, France  (Rapporteur)

a       Professor V.A. Nasonova, Institute of Rheumatology,
           Academy of Medical Sciences of the USSR, Moscow, USSR

a,d     Professor H.D. Tandon, New Delhi, India  (Temporary
            Adviser) (Chairman)

a       Professor Yan Jianbo, Haerbin Medical University,
           Haerbin, People's Republic of China

a,b     Professor H. Yanagawa, Department of Public Health,
           Jichi Medical School, Minamikawachi, Tochigi-ken,

a       Professor Yang Guangqi, Institute of Health, China
           National Centre for Preventive Medicine, Beijing,
           People's Republic of China  (Vice-Chairman)

a       Professor Yu Weihan, Haerbin Medical University,
           Haerbin, People's Republic of China


a       Dr Chen Junshi, Department of Nutrition and Food
           Hygiene, Institute of Health, China National Centre
           for Preventive Medicine, Beijing, People's Republic
           of China

a       Dr Chen Xiaoshu, Institute of Health, China National
           Centre for Preventive Medicine, Beijing, People's
           Republic of China

a       Dr Chen Qing, Department of Environmental Health,
           School of Public Health, Beijing Medical University,
           Beijing, People's Republic of China

a       Dr Dai Yin, National Institute of Food Safety Control
           and Inspection, China National Centre for Preventive
           Medicine, Beijing, People's Republic of China

a       Dr He Xingzhou, Department of Environmental Hygiene,
           Institute of Health, China National Centre for
           Preventive Medicine, Beijing, People's Republic of

a       Dr Li Guangshen, Institute of Endemic Disease, Norman
           Bethune University of Medical Sciences, Changchun,
           Jilin province, People's Republic of China

a       Professor Li Yurui, Division of Pneumoconiosis, Department
           of Labour Hygiene, Institute of Health, China National 
           Centre for Preventive Medicine, Beijing, People's 
           Republic of China 

a       Dr Liu Yuying, Division of Industrial Toxicology,
           Department of Labour Hygiene, Institute of Health,
           China National Centre for Preventive Medicine,
           Beijing, People's Republic of China

a       Dr Lu Boqin, Division of Industrial Toxicology, Department
           of Labour Hygiene, Institute of Health, China National 
           Centre for Preventive Medicine, Beijing, People's 
           Republic of China 

a       Dr Ma Tai, Tianjin Medical College, Tianjin, People's
           Republic of China

a       Professor Niu Shiru, Institute of Health, China
           National Centre for Preventive Medicine, Beijing,
           People's Republic of China

a       Dr Qin Yuhui, Institute for Environmental Health
           Monitoring, China National Centre for Preventive
           Medicine, Beijing, People's Republic of China

a       Dr Su Zhi, Department of Health and Epidemiological
           Control, Ministry of Public Health, Beijing,
           People's Republic of China

a       Professor Tan Jianan, Institute of Geography, Chinese
           Academy of Sciences, Beijing, People's Republic of

a       Professor Wang Huizhou, Department of Nutrition and
           Food Hygiene, Institute of Health, China National
           Centre for Preventive Medicine, Beijing, People's
           Republic of China

a       Dr Wang Juning, Division of Environmental Toxicology,
           Department of Environmental Hygiene, Institute of
           Health, China National Centre for Preventive
           Medicine, Beijing, People's Republic of China

a       Dr Xu Genlin, Office of Research Management, Institute
           of Health, China National Centre for Preventive
           Medicine, Beijing, People's Republic of China

a       Dr Xu Guanglu, Research Laboratory of Keshan Disease,
           Xian Medical University, Xian, People's Republic of

a       Dr Yo Peipei, Division of Pneumoconiosis, Department
           of Labour Hygiene, Institute of Health, China
           National Centre for Preventive Medicine, Beijing,
           People's Republic of China

a       Dr Zhen Xiwen, Institute of Epidemiology and Microbiology, 
           China National Centre for Preventive Medicine, Beijing, 
           People's Republic of China 


e       Dr T. Kjellström, Prevention of Environmental Pollution,
           World Health Organization, Geneva, Switzerland

a       Dr M. Mercier, International Programme on Chemical
           Safety, World Health Organization, Geneva,

a       Dr M. Mitrofanov, Division of Noncommunicable
           Diseases, World Health Organization, Geneva,

a,d     Dr J. Parizek, International Programme on Chemical
           Safety, World Health Organization, Geneva,
           Switzerland  (Secretary)

d       Dr A. Prost, Division of Environmental Health, World
           Health Organization, Geneva, Switzerland

a Attended the Task Group meeting in Beijing, 28 October -
  2 November 1985.
b Chairman of a subgroup of the Beijing Task Group meeting.
c Rapporteur of a subgroup of the Beijing Task Group meeting.
d Attended the editorial meeting in Geneva, 28 April - 2 May 1986.
e Available for discussions at the Geneva editorial meeting on a 
  part-time basis.


    Every effort has been made to present information in the 
criteria documents as accurately as possible without unduly 
delaying their publication.  In the interest of all users of the 
environmental health criteria documents, readers are kindly 
requested to communicate any errors that may have occurred to the 
Manager of the International Programme on Chemical Safety, World 
Health Organization, Geneva, Switzerland, in order that they may be 
included in corrigenda, which will appear in subsequent volumes. 

                      *    *    *


    The prevention and control of locally endemic diseases is one 
of the essential components of primary health care.  The IPCS 
Environmental Health Criteria documents dealing with mycotoxins 
(WHO, 1979b), aquatic biotoxins (WHO, 1984b), and pyrrolizidine 
alkaloids (WHO, in press), describe situations in which the 
prevention and control of outbreaks of locally-occurring diseases 
were made possible by the successful elucidation of the chemical 
etiology of the diseases.  The strategies used in this disease-
oriented approach, including the sequence and character of the 
questions addressed, differ from those used in predictive 
toxicology, where the starting point is not a disease but a known, 
defined chemical, evaluated for possible health effects. 

    When developing the methodology component of the International 
Programme on Chemical Safety, it was evident that there was a need 
for a document that would summarize the principles of studies aimed 
at the elucidation of the role of chemicals in the etiology of 
diseases, benefiting from the experience of experts who have 
successfully carried out such studies.  The disease-oriented 
approach in relation to chemical exposures and malignant and 
occupational diseases has been dealt with in other programmes of 
the World Health Organization (WHO), including the International 
Agency for Research on Cancer (IARC), and will not be discussed 
specifically in this document.  The document focuses on the 
principles of studies dealing with endemic non-malignant diseases 
and outbreaks of diseases of unknown origin and the possible role 
of exposure to chemicals in their causation. 

    Situations in which populations are permanently resident in an 
area and mainly dependent on locally produced food, offer 
conditions favourable for the occurrence of locally endemic 
diseases and also for the study of these diseases.  These 
conditions are often found in developing countries and much can be 
learned concerning methods of studying the problem of the chemical 
etiology of diseases, from studies carried out in such regions.  
Thus, it was of great advantage that the Ministry of Public Health 
of the People's Republic of China agreed that the Institute of 
Preventive Medicine and its Institute of Health, Beijing, would 
host the IPCS Task Group meeting on the principles and criteria for 
establishing the chemical etiology of diseases of uncertain 
causality as a basis for their prevention, together with a joint 
conference on Kashin-Beck disease, a highly disabling disease of 
permanent character affecting a very large group of people in 
endemic areas in China. 

    The resulting draft document was finalized at an editorial 
meeting held in Geneva from 28 April to 2 May 1986 under the 
guidance of PROFESSOR H.D. TANDON (Chairman of the Task Group).  
Background papers, prepared by the participants at the request of 
the Secretariat, for the IPCS Task Group meeting in Beijing, are 
listed in Appendix I.  The Chairman of the Task Group, responding 
to a request of the Secretariat, prepared another paper summarizing 
the conceptual framework that had been used in several studies in 

the past and had led to the successful identification of the 
chemical etiology of certain diseases and their prevention and 
control.  This paper, which was used as a guide for the Task Group 
during discussions in plenary and subgroups and was further 
developed at the editorial meeting, is presented in Appendix II.  
The summary report of the Beijing meeting, reviewing the experience 
on Kashin-Beck disease, is presented in Appendix III. 

    The help of the host Institutions in Beijing, the organizers of 
the meetings, and all participants, including those who finalized 
the document at the editorial meeting in Geneva, is gratefully 
acknowledged.  It is hoped that their life-long experience and 
enthusiastic involvement throughout the preparation of this 
publication will make it useful to all concerned with the 
prevention and control of diseases of possible chemical etiology. 

    The United Kingdom Department of Health and Social Security 
generously supported the costs of printing. 


    It is suspected that some endemic diseases or sudden outbreaks 
of unknown diseases in several regions of the world might be 
related to exposure of affected populations to one or more natural 
or man-made chemical substances. 

    This publication is based on experience from studies and 
investigations in which the chemical origin of several unknown or 
unusual pathological conditions has been successfully identified.  
The basic principles of these studies are summarized and a step-
by-step approach is described starting with the recognition of the 
disease pattern among the affected people, evaluation of the 
magnitude of the problem (number of people affected, geographical 
impact area, etc.), and collection of clues pointing to, and 
eventual identification of, its chemical etiology.  Such an 
approach is called the disease approach.  The search for etiology 
begins after the recognition and description of the health problem 
being investigated. 

    The second section of the paper deals with the epidemiological 
approach.  The search for specific determinants is described, 
including methods that should be used, and how data should be 
analysed.  This is followed by a description of the toxicological 
studies necessary for testing hypotheses on possible exposure to 
various substances, the hypotheses having been generated through 
the combined evaluation of clinical and epidemiological data.  
Problems, including bias, in establishing the causal relationship 
between one or several suspected agents and the observed disease 
patterns are also considered. 

    A further section deals with steps that, in the opinion of the 
Task Group, should be taken when the chemical etiology of an 
outbreak of a disease has been recognized.  The publication ends 
with a section on the need for international cooperation in the 
field of recognition of the chemical etiology of certain diseases. 

    A sequential list of activities that has been followed in 
several successful studies and can be used as a checklist, when a 
similar approach needs to be developed, is included as Appendix II. 

    The meeting at which this publication was prepared was held in 
the People's Republic of China together with another international 
meeting organized jointly by the IPCS, the WHO Regional Office for 
the Western Pacific, and the health authorities of the People's 
Republic of China.  The second meeting dealt with the present 
status of research on Kashin-Beck disease, and osteoarthrosis 
deformation, which is endemic in certain parts of Asia and, in 
certain regions of the People's Republic of China, has affected 
more than one million inhabitants, mainly children.  This disease 
is given special attention, because it affects a very large segment 
of the population in a developing country and because of growing 
evidence that deficiency of a certain essential nutrient combined 
with exposure to a specific chemical may be the factor responsible 
for this peculiar disease and its specific endemicity. 


    The prevention of disease constitutes a major component in 
world-wide efforts to achieve "Health for all by the year 2000".  
Preventive measures must be directed towards the control or 
eradication of specific etiological factors that cause human 
diseases.  Thus, a prerequisite for successful prevention is 
adequate knowledge concerning disease causation. 

    While several diseases are known to be heritable and therefore 
to have a genetic etiology, other diseases are known to be caused 
by specific environmental factors, as in the case of intoxications, 
infections, or nutritional deficiencies.  However, at present, the 
etiology of most human diseases is not known or is only partially 
known, and methods for primary prevention based on recognition of 
etiology can only be considered for a limited number of diseases.  
The search for etiological factors will therefore achieve 
increasing importance as a basis for future preventive measures.  
In this regard, diseases caused by chemical factors are of 
particular interest, and their effects on human health have not 
been sufficiently investigated, even though exposure to naturally-
occurring chemicals has always been a part of human life.  With 
further industrialization as an essential step in development, 
people are likely to be exposed to more and increasingly diverse 
chemicals, even though careful steps may be taken to monitor and 
control their proper use and the safe disposal of industrial 
wastes.  New chemicals are developed for a variety of purposes, 
both industrial and non-industrial, and the lack of preventive 
measures, or insufficient application of such measures, may result 
in toxic effects in populations exposed to them.  Furthermore, 
exposure to chemicals or combinations of chemicals under various 
conditions of human life may result in toxic effects, not 
previously recognized.  Chemicals in the form of fertilizers and 
pesticides are particularly essential in modern agriculture, to 
meet the increasing needs for food, and exposure of the general 
population to the residues of these chemicals is increasing.  In 
most parts of the world, the agricultural community is often not 
sufficiently informed about the proper use of chemicals and the 
associated hazards, and dangerous exposures are likely.  The 
episode of alkylmercury poisoning (WHO, 1977) is an example of 
large-scale casualties caused by such accidents. 

    Exposure to chemicals may cause human disease in several ways.  
First, a certain disease may result directly from exposure to a 
specific chemical compound, for example, Minamata disease, which is 
caused by exposure to methylmercury (WHO, 1977).  Second, exposure 
to a chemical may be only one of several factors contributing to 
the development of a disease, and, thus, be part of a multicausal 
relationship.  Itai-itai disease is an example of a disease with a 
complex etiology, caused by several factors in combination with 
cadmium toxicity (Tsuchiya, 1978).  Chemical exposure may also 
aggravate a pre-existing disease.  For example, air pollution with 
nitrogen oxides will provoke air-way symptoms in patients with 
respiratory diseases (WHO, 1979a).  Thus, exposure to chemicals may 
constitute a leading factor in the development of a range of human 

    An important determinant of health is the balance between the 
status of the  milieu intérieur and that of the  milieu extérieur.  
Excess or deficiency of naturally-occurring chemicals in the 
natural environment or the presence of extraneous chemicals may 
alter this balance by making the body tissues more vulnerable.  
Fluorosis is known to be endemic in several parts of the world 
because of excess fluorides in the drinking-water; similarly, there 
are large areas where goitre is endemic, because of iodine 
deficiency in the environment.  Nutritional factors play an 
important role in both exposure and susceptibility to various 
chemical agents. 

    The practising physician may not be familiar with the ever 
increasing diversity of chemicals that can be hazardous for man, 
nor with the initial symptoms and signs of toxicity.  This is one 
of the reasons why the establishment of a cause and effect 
relationship between disease and exposure to chemical agents is 
less straightforward than between disease and infections.  Episodes 
of chemical poisoning in the form of isolated cases, groups of 
cases, or outbreaks, which present a pattern of disease that does 
not fit in with the symptom complexes of known diseases, 
particularly in developing countries, are likely to be first 
considered as of infectious origin or to be the result of 
malnutrition (Anon., 1984).  The Afghan outbreak of veno-occlusive 
disease was considered to be a water-borne infection, until the 
chemical etiology was discovered through recognition of a plant 
growing among the staple food crop of wheat.  The chemicals 
responsible for the disease were the pyrrolizidine alkaloids in the 
seeds of the plant, which were mixed with the grain (Tandon & 
Tandon, 1975). 

    Generally speaking, there are no sets of clinical 
characteristics of diseases that, alone, could lead the 
investigator to suspect chemical etiology and exclude other causes.  
It is only when the total context of the disease pattern and the 
circumstances of its appearance is considered that such an etiology 
might be suspected, though some clues may emerge, even from the 
initial epidemiological characteristics. 

    The epidemiological characteristics of diseases of unknown 
etiology may vary in the following ways: 

    (a)  A sudden outbreak of a disease that is considered "new" is 
         often attributed to an unknown infectious agent.  The 
         search for the etiology should take into account factors 
         of a chemical nature.  An evaluation of the 
         epidemiological pattern of the disease might provide 
         useful orientations that can be fruitfully pursued.  For 
         example, the outbreak of liver disease in India, which was 
         later confirmed to be due to aflatoxin exposure (Tandon et 
         al., 1977, 1978a), was initially considered to be one of
         infectious hepatitis, because the dominant features of the 
         disease were jaundice and other systemic symptoms that 
         suggested hepatocellular failure.  The initial 
         epidemiological characteristics of the disease indicated 
         that transmission of the virus was highly unlikely to be a 
         causal factor, and this prompted the search for another 
         environmental factor. 

    (b)  Endemic diseases continuously occur and recur in defined 
         geographical areas.  Although such diseases constitute a 
         chronic health problem that could be studied by 
         conventional epidemiological methods, many endemic 
         diseases have an environmental etiology of unknown nature.  
         For example, according to the recent estimates, Kashin-
         Beck disease has affected about 2 million individuals in 
         certain endemic regions of China, but the specific 
         chemical etiology has so far escaped discovery (Appendix 

         When the exposure is not sufficient to result in the 
         clustering of cases, the disease may remain unnoticed or 

    (c)  Some commonly occurring diseases may include exposure to 
         chemicals as a risk factor.  However, the role of 
         widespread, long-term, low-level complex exposure in the 
         multifactorial etiology of such diseases is more difficult 
         to establish and this problem is not addressed in this 

    In searching for an etiology, it is important to recognize the 
source of the chemical.  Diseases that have been identified as 
chemically induced, have been associated with various chemicals 
with the following origins: 

    (a)   Naturally-occurring inorganic chemicals

    There are many naturally-occurring inorganic chemicals that 
have been found to be toxic for man, e.g., mercury, lead, and 
cadmium.  Although these chemicals are neither created nor 
destroyed by man, geochemical conditions, natural processes, such 
as accumulation in certain biota, and industrial activities may 
result in their widespread but uneven distribution, or in the 
formation of new compounds that may be more or less toxic than the 
naturally-occurring forms. 

    Diseases can also be caused by excessive exposure to inorganic 
chemicals that may be beneficial or even be a metabolic requirement 
at low levels.  A relationship has been established between 
skeletal fluorosis and the long-term elevated intake of fluoride 
(WHO, 1984a). 

    (b)   Chemicals of plant origin

    Several episodes of disease have been reported resulting from 
the accidental contamination of food crops by certain weeds and 
their seeds.  Thus, contamination of staple food crops with 
pyrrolizidine alkaloid-containing seeds has caused large-scale 
outbreaks of veno-occlusive disease in Afghanistan (Tandon & 

Tandon, 1975; Mohabbat et al., 1976) and the USSR (Dubrovinski, 
1952).  Furthermore, veno-occlusive disease may also result from 
the use of pyrrolizidine alkaloid-containing herbs as traditional 
home remedies, as seen in the West Indies (Stuart & Bras, 1955) and 
elsewhere (Huxtable, 1980; Ridker et al., 1985). 

    Staple food sometimes contains toxic substances that are 
removed during food processing or do not represent a hazard for 
human health under normal circumstances.  However, as seen in 
Mozambique, modifications in plant constituents induced by 
environmental changes, together with changes in methods of food 
preparation, and patterns of consumption, can lead to acute or 
subacute poisoning.  An outbreak of spastic paraparesis in 
Mozambique was shown to be related to cyanide intoxication caused 
by cassava.  During a severe drought, the cyanide content of the 
cassava increased naturally.  Moreover, famine forced most families 
to turn to bitter cassava, which has a higher cyanide content, and 
to eat it after drying it for a few days only, whereas several 
weeks are required for proper detoxication (Mozambique Ministry of 
Health, 1984). 

    (c)   Microbial toxins (chemicals produced by microscopic fungi, 
          algae, and bacteria)

    Exposure to toxins from fungi (mycotoxins) takes place mainly 
through the ingestion of contaminated foods, though airborne 
exposure to fungal spores containing mycotoxins is also possible 
(WHO, 1979b).  Contamination of foods of plant origin takes place 
generally in the post-harvest period through invasion by moulds.  
It is difficult to detect by conventional food inspection practices 
because of the microscopic appearance of the fungi.  An example of 
mycotoxin-associated disease is the toxic effects caused by 
aflatoxins in food grains (WHO, 1979b).  Exposure to algal toxins 
is generally caused through the ingestion of fish and shellfish 
that have been feeding on toxic microscopic algae (plankton) and 
thereby retaining part of the algal toxins, without actually 
showing any organoleptic changes.  Examples of such diseases are 
paralytic shellfish poisoning caused by saxitoxin and derivatives, 
and diarrhoeic shellfish poisoning caused by okadaic acid and 
derivatives (WHO, 1984b).  Diseases induced by bacterial toxins are 
caused by inadequate food processing, during which the toxin-
producing bacteria may infect foods and produce toxins, just prior 
to consumption.  For example, staphylococcal food poisoning is 
caused by enterotoxins from  Staphylococcus aureus, and botulism, 
by neurotoxins from  Clostridium botulinum growing in processed 
meat, fish, and vegetables. 

    (d)   Man-made chemicals

    A number of acute outbreaks and incidents of illness have been 
found to be caused by exposure to pesticides, fertilizers, 
germicides, or industrial chemicals.  Some of these episodes have 
been explained as outbreaks of acute poisoning caused by the 
accidental contamination of food, for example by parathion (Diggory 
et al., 1977), or of items of household and personal use, such as 

baby powder, by hexachlorophene (Martin-Bouyer et al., 1982), and 
laundry rinses, by pentachlorophenol (Robson et al., 1969).  
Although only short-term exposure may have occurred, health effects 
may be permanent, or recovery may be very slow as in the Yusho 
episode in Japan where the deceased people had ingested a mixture 
of polychlorinated biphenyls, dibenzofurans, and quarterphenyls 
(Kuratsune et al., 1969) or in Turkey where liver disease and 
porphyria cutanea tarda resulted from contamination of grain with 


    The nature and magnitude of the problem, as well as the 
facilities available for investigating diseases possibly caused by 
chemicals, vary from country to country for a number of reasons 
including the extent to which the health services have been 
developed, and whether stray cases or outbreaks of toxic disease 
are being studied.  Countries with well-developed infrastructures 
in the health services usually have rigid control systems with 
regard to food quality, sanitation, and water supplies, and good 
investigative facilities.  Reasonably good health-care facilities 
are available, even in outlying areas.  If outbreaks of chemically-
induced diseases occur, they are usually the result of a short-term 
exposure to a toxic chemical, affecting a limited number of cases, 
which are likely to be noticed as soon as they appear.  Thus, 
expeditious steps can be taken for their investigation or control. 
Investigation and control of outbreaks in countries with 
inadequately developed health services need a different approach, 
though the principles may be the same. 

    In this publication, a strategy is discussed, which might be 
used in the investigation of episodic or endemic diseases of 
suspected chemical etiology.  Instead of asking what are the 
effects of a specific chemical, the question can be reversed to ask 
which chemicals might cause a particular health effect.  It may be 
difficult to distinguish a chemically-induced from an infectious 
disease and to identify the etiological chemical agent.  Clues are 
often elusive and inextricably mixed with day-to-day occurrences or 
the "not-so-unusual" disease phenomena affecting a population.  The 
search for an etiology often necessitates sequential planning for a 
progressive build up of clues. 

    The identification of the chemical causes of a disease involves 
a group of interrelated disciplines, in particular pathology, 
epidemiology, and laboratory medicine and toxicology.  The approach 
may be a straightforward process when a large group of people is 
exposed to a chemical with known toxicity, but this may not always 
be the case.  The search for an etiology will depend on 
scientifically clear evidence of linkages between exposure to a 
chemical, the biological effects, and subjective clinical symptoms. 

    Appendix II includes a description of a conceptual framework of 
studies on outbreaks (episodes), which resulted in the successful 
identification of their chemical etiology and, through this, their 
control and prevention.  However, it should be said at the outset 
that it is not a blueprint for action, but an example that could be 
suitably modified as the situation demands.  It was designed to 
investigate the causes of diseases in which chemicals in the 
environment were the principal, rather than a minor, contributory 

    Appendix III includes a summary report on the present state of 
research concerning the etiology of a wide-spread endemic disease 
in which exposure to certain environmental chemicals is considered 
an important etiological factor. 

    In the following sections, the approaches that should be 
considered simultaneously, when the chemical etiology of a disease 
is being investigated, are discussed at some length. 


4.1.  General Background

    To investigate the etiology of outbreaks of diseases caused by 
chemicals, the "disease approach" is the first step in the 
methodological framework.  Epidemiological and toxicological 
approaches are then developed as analytical tools to generate valid 
etiological hypotheses and to test them at each stage of the 
investigation.  The steps or phases recommended are intended to be 
progressive and the decision to terminate or modify the process 
might be considered at any phase, if appropriate. 

    In order to investigate outbreaks of disease, or the endemicity 
of a disease, it is important to be familiar with the general 
disease patterns in a specific geographical area.  The incidence 
and types of diseases may vary, to some extent, in different 
countries and may change with socioeconomic conditions and 
industrial activity.  However, awareness of the epidemiological 
pattern in a given population will make it possible to recognize 
changes in disease patterns, the occurrence of new diseases, the 
sudden outbreak of epidemics of infectious diseases, outbreaks of 
poisoning, or the presence of endemic diseases in localized 
geographical areas.  The recognition of such diseases is usually 
based on observations of health personnel that the frequency of a 
common disease has increased, that a hitherto unknown constellation 
of clinical manifestations has been encountered, or that the age-
specific incidence of a disease is shifting.  When such 
observations are reported, they must be critically evaluated to 
determine whether these observations are truly abnormal.  For 
example, it is possible that a physician with a special interest in 
certain diseases may simply recognize them more frequently, or that 
diseases of different etiological factors may be erroneously 
grouped together. 

    The methodology of epidemiology as described in a recent 
publication (WHO, 1983) outlines choices of study design, methods 
for the assessment of exposure, and signs and symptoms for the 
ascertainment of health effects.  However, the precise etiology of 
the condition under study cannot be established from the resulting 
association alone.  In addition, there may be lack of information 
on exposure, evidence of combined toxic exposures, or, perhaps most 
important of all, lack of proof or evidence supporting hypotheses 
linking exposure to specific environmental factors with the 
disease.  Several disciplines must be involved in providing precise 
identification of etiological factors. 

    Disease investigation begins with awareness of an apparent and 
unusual number or cluster of cases with a clinically characterized 
disease entity (index cases as discussed below).  Therefore, the 
initial investigations must almost always involve some level of 
epidemiological investigation.  An unusual clinical phenomenon in a 
population may: 

    (a)  be characterized by pathognomonic signs that do not occur 
         in a disease of known etiology; 

    (b)  be associated with combination of non-specific clinical 
         features, signs, symptoms, and laboratory and other data 
         that do not fit into a known disease category;

    (c)  constitute a cluster of cases of a disease that normally 
         occurs with a low frequency; or 

    (d)  constitute an endemic disease of unknown etiology.

    After ascertaining that there is an unusual clinical phenomenon 
in the population, the search for a chemical etiology and 
subsequent action can proceed in the following phases: 

    (a)  descriptive phase, in which the disorder is characterized 
         by clinical, pathological, and epidemiological features;

    (b)  hypothesis-generation phase, in which a hypothesis is
         assumed concerning the possible etiological factors, on 
         the basis of clues obtained from the initial studies; 
         further supportive clues are searched for; 

    (c)  hypothesis-testing phase, in which the clues obtained are 
         tested by the identification of biological markers of 
         exposure or injury, detailed pathological studies on 
         diseased tissues in man and affected animals, and 
         toxicological studies on animals; 

    (d)  follow-up evaluation, in which follow-up action is taken, 
         if the causative agent is successfully identified.

These steps are outlined in the Appendix II.

4.2.  Recognition of Index Cases

    Index cases refer to the first reported case or cluster of 
cases of the disease under study.  It may happen that the first 
reported case is not the first one to occur, and that the true 
index case has remained unnoticed.  A retrospective analysis of all 
available information should always attempt to trace the disorder 
backwards to the true index case.  In the rural areas of some 
developing countries, these cases may be identified by paramedical 
personnel or practitioners of traditional medicine.  In urban 
areas, they may initially come to the attention of the emergency 
medical services, or, in the industrial sphere, be identified by 
occupational medicine specialists.  In order to reduce, or possibly 
exclude, distractors from among the cases included in the affected 
category, it is essential to define the characteristics of such 
index cases.  Typically, the index cases exhibit severe forms of 
the disease with overt clinical manifestations.  At this stage, the 
whole range of signs and symptoms associated with the disease may 
not be recognized, and index cases should later be thoroughly 
evaluated and a general case definition developed. 

    Once it is presumed that a normally occurring illness is 
suddenly occurring at a higher frequency (or has reached epidemic 
proportions), or that there is an outbreak of a disease that has 
not been observed previously, it must be established whether a true 
outbreak exists.  For instance, it is possible that certain 
conditions in the general population may be overlooked, until 
special interest develops or appropriate diagnostic methods are 
introduced, with the result that suddenly such conditions are 
reported more frequently.  This increase merely represents a 
reporting artifact and not a true increase.  Furthermore, a variety 
of diseases may be thought to represent the same condition and the 
increase in this condition is again merely a reporting artifact. 

    After having defined the diagnostic criteria on the basis of 
identified index cases, a search should be carried out to identify 
all suspect cases.  The principles of epidemiological studies are 
described in detail in a previous publication (WHO, 1983).  Disease 
characterization can be carried out by a sequential approach.  
Initial screening of the population aimed at identifying all cases 
suspected of being involved in the outbreak is followed by phases 
in which the disease becomes progressively more clearly defined as 
more specific clinical and laboratory criteria are applied.  As an 
example, in the investigation of the aflatoxin outbreak in India 
(Tandon et al., 1977), all cases of jaundice associated with 
hepatomegaly and other systemic symptoms were included in the 
primary screening.  When liver biopsies were taken, features 
characteristic of acute infectious hepatitis were seen in 
occasional cases, and these were excluded at the stage of case 
definition, described in section 4.4. 

4.3.  Screening of Populations for Suspected Cases

    After the index cases have been evaluated, a decision may be 
made to screen the affected community.  This decision is not 
automatic and must be based on an assessment, by appropriately 
trained medical and public health personnel, that an outbreak of 
the disease has occurred and may be more widely distributed than 
appears from the index cases.  The aim of screening the population 
is to estimate the total incidence or prevalence of a set of signs 
and symptoms considered to suggest a disease related to the 
suspected etiology.  Such screening in developing countries is 
frequently carried out by paramedical personnel.  Accordingly, the 
tests need to be easy to use, e.g., standard questionnaires based 
on information obtained from the index cases.  An example would 
include simple tests of motor coordination to evaluate nervous 
system changes, without the use of specialized medical equipment. 
Personal history should include age, sex, occupation, life-style 
variables, and place and duration of residence.  In addition, past 
medical history should include relevant data on previous and 
current diseases, pregnancy, and lactation. 

    The number of persons to be included in the initial screening 
depends on the specific circumstances of the outbreak.  Clearly, 
the key limiting factors are economic resources and available 
personnel.  The efficacy of the screening will be improved by 

eliciting the full cooperation of the persons potentially affected 
by the disease.  The benefits for the population of participating 
in the primary screening should be emphasized.  Support from the 
affected person's family and, for example, the village or tribal 
heads, is helpful in conducting primary screening.  In more 
urbanized areas, the support of community groups or factory 
workers' organizations could be beneficial. 

4.4.  Case Definition

    At this stage of the investigation, identification of different 
stages of the disease becomes possible.  Cases range from those 
with the most severe symptoms to those with only subclinical 
effects.  The case definition should not be so restrictive that 
only the "tip of the iceberg" is identified.  It should be specific 
enough to separate the disease of concern from diseases of other 
origin.  Ideally, one sign or symptom would be pathognomonic of the 
disease under investigation.  However, this is rarely the case.  
Generally, a number of signs and symptoms and the pattern of their 
appearance are used to identify the disease.  Individually, these 
signs and symptoms would not be either sensitive or specific.  
However, the clustering and relative severity of these signs and 
symptoms greatly increase their use in identifying cases of the 

    Procedures used in case definition are generally much more 
reliable and complex, and involve laboratory support and techniques 
not applicable in the initial screening.  This part of the study 
requires more highly trained personnel than the initial screening.  
The criteria are based on the most severe cases at the initial 
stages and must therefore be considered provisional, since they 
will not include mild disorders and subclinical effects.  The case 
definition should include: 

    (a)  Identification of the target organ or organs and the 
         characteristic effects.  It is critical to recognize that 
         organ systems have limited types of response and that 
         these are rarely pathognomonic for a disease caused by a 
         particular chemical. 

    (b)  Identification of specific groups that appear to be
         particularly vulnerable, e.g., infants, or persons living 
         within a certain radius of a chemical industry. 

    A description of the clinical appearance of the disease should 
include the signs and symptoms, clinical course of the disease, and 
pathological findings.  Pathological study of diseased human or 
animal tissues, early in the outbreak, might provide useful 
etiological clues.  If autopsies are not available, biopsies from 
patients or autopsies of affected domestic animals, as mentioned in 
section 4, should be carried out.  More detailed information should 
be gathered concerning the extent of the problem, i.e., precise 
figures on morbidity and mortality rates and time sequence. 

    Analysis of the demographic data obtained during screening will 
indicate whether or not there is a subpopulation at high risk, 
e.g., residents in a given area, an occupational group, young 
children, or persons with pre-existing problems.  The spectrum of 
clinical severity may differ among groups of individuals affected 
by toxic chemicals to a greater extent than that among patients 
with an infectious disease.  The wide variation in involvement may 
be due to differences in the levels and lengths of exposure and 
differences in host susceptibility, because of differences in age, 
nutritional status, etc., which should be specified in detail 
during the process of identification. 

    At this phase in the study, it is desirable to review 
toxicological information on the potential health effects of the 
toxic chemical suspected of playing a role in the etiology of the 
disease (section 6).  Comparison may identify clinical or 
biochemical effects that have not been previously investigated and 
may provide a basis for confirming the relationship between the 
toxic agent, the case definition, and observed effects.  Finally, 
toxicological studies may provide predictive information regarding 
prognosis, including the progression or reversibility of the health 
effects observed. 

    Because the background prevalence of signs and symptoms in the 
general population is not known, it is appropriate at this stage to 
survey all persons who appear to be affected by the disease.  The 
inclusion of a comparison group is essential, in order to identify 
a tentatively discriminating factor. 

4.5.  Case Identification

    The definition of the clinical entity, based on rigid quality 
control, high specificity and sensitivity, results in the 
identification of: 

    (a)  early symptoms that may not have been recognized during 
         the initial screening; 

    (b)  associated clinical pathological/radiological features of 
         the disease; 

    (c)  characteristic pathological features in the affected
         tissues; and

    (d)  complications beyond the acute phase, and sequelae.

    In this phase of the analysis, the population is screened again 
to identify borderline, subclinical, or latent cases using 
established diagnostic criteria and specific biological markers.  
This may also give a more precise idea about the magnitude of the 

4.6.  Importance of Pathological Studies

    The pathological study of biopsy or autopsy specimens may 
provide the crucial clue(s) in the identification of the etiology 
of a disease.  The proper conduct of pathological studies may 
contribute to the formulation of hypotheses regarding etiology, and 
influence the selection of subsequent studies.  Morphological 
changes in the principal target organ may prove to be pathognomonic 
of the etiological agent.  In the investigation of an outbreak of a 
disease in India, the presence of syncitial giant cells in human 
liver tissue and recognition of the fact that an identical lesion 
had been previously observed in the liver of rhesus monkeys exposed 
to aflatoxins, suggested the etiological role of aflatoxins in this 
human disease outbreak (Tandon et al., 1977, 1978a).  The 
morphological changes observed may also help to exclude infectious 
disease as a cause of the illness. 

    For various reasons, there may be difficulties in obtaining 
human autopsy material.  In such an event, biopsy of the diseased 
organ or examination of autopsy material from field animals 
suffering from a disease identical to that in man may prove useful, 
as again happened in the aflatoxicosis outbreak (Tandon et al., 
1978a).  The biopsy could be carried out as part of a diagnostic or 
therapeutic procedure for the benefit of the patient, for example a 
liver or a kidney biopsy could be carried out following 
paracentesis, or the bony tissue, resected as a part of corrective 
surgery, could be examined.  Histological appearance may identify 
the specific target tissue and the affected cell type or could 
decisively indicate infection or some other specific disease.  
Descriptions should be in the internationally recognized standard 
medical nomenclature. 

    The usefulness of pathology specimens may be enhanced by 
providing advice and materials for proper tissue fixation, and 
storage instructions.  Parallel sampling for chemical analysis 
should always be considered and such specimens should be stored by 
freezing and without fixation. 

4.7.  Reporting Systems and Case Records 

    In most countries, reporting systems exist for recording 
infectious diseases.  A similar approach would be useful for the 
reporting of outbreaks and epidemics of diseases of unknown origin. 

    Delays in notifying central health authorities may occur for 
many reasons.  If different patients are treated by different 
physicians, there may be a time lag before a disease outbreak is 
recognized.  The delays should be avoided, as far as possible, as 
prompt and concise reporting is necessary for establishing the 
etiology of the disease and controlling the outbreaks.  Biological 
specimens should be secured, especially from the index cases, and 
the time interval between onset of illness and biological sampling 
should be noted.  Even initial studies might provide useful clues.  
Records should be kept of the index cases, if further evaluation or 
periodic reexamination of index cases is thought to be warranted, 

e.g., for the development of a case registry and long-term, 
follow-up studies.  Such a registry would allow the investigators 
to study the natural history (or progression) of the disease.  
Unfortunately, a number of index cases may be lost to follow-up, 
when it is not initially recognized that an outbreak is occurring.  
On the other hand, development of registries is not always 
desirable or cost productive.  If long-term follow-up of affected 
persons is deemed desirable, certain possible constraints should be 

    The following problems are generally faced in the development 
of a case registry: 

    (a)  high costs and lack of financial support;

    (b)  cases of chemical toxicity are generally not reportable;

    (c)  lack of suitably trained medical and paramedical 
         personnel, capable of maintaining a registry; 

    (d)  mobility of populations;

    (e)  lack of cooperation of health personnel;

    (f)  inconsistency of disease nomenclature.

    The problems encountered in recognizing and recording diseases 
of chemical etiology are illustrated by the historical evidence on 
lead poisoning (Grandjean, 1975; Mahaffey, 1985).  The failure to 
recognize lead exposure as a cause of the disease was due to:  (a) 
failure to appreciate the importance of individual susceptibility; 
(b) unsuspected sources of exposure; (c) non-specific pathological 
changes; and (d) classification into several ill-defined clinical 
syndromes.  With the occurrence of ubiquitous lead pollution, there 
may be other insidious health effects caused by past or long-term 
exposure, which may be difficult to identify or recognize. 


5.1.  General Background

    One of the important steps, when searching for the etiology of 
diseases, is to establish and validate associations between the 
occurrence of the disease and exposure to one or more common 
factors that could be considered as determinantsa.  The classical 
epidemiological approach is to generate a hypothesis from 
preliminary information collected through descriptive study and 
then test it in an analytical epidemiological study of appropriate 
design, as described in detail by WHO (1983).  Although this 
sequence is logical, the exploration of the chemical etiology of a 
disease may not necessarily follow this sequence, particularly when 
an acute outbreak of disease occurs.  In such situations, rapid 
recognition and resolution of the problem is of the utmost 
importance.  Although a series of steps is outlined below, in 
practice, they will often have to be carried out almost 

    The early recognition of an outbreak of, or unusual increase 
in, disease depends on careful observation of cases and a reliable 
reporting network.  Expeditious investigation of the 
outbreak/occurrence of cases cannot be overemphasized.  The 
investigator should obtain as much information as possible, such as 
the geographical extent of the outbreak, the population at risk, 
the number of cases, distribution of cases in the population, 
clinical manifestations, time of onset of the outbreak, and whether 
similar outbreaks have occurred in the past.  This preliminary 
information will enable the investigator to develop the tentative 
hypotheses necessary to decide on the technical support systems 
needed.  Additional advice can be obtained from the pertinent 
scientific literature and from international agencies and other 
institutions in relation to the nature of samples that should be 
collected, and the names and addresses of specialized laboratories 
for the analysis/identification of toxic materials and biological 
fluids/tissues from diseased animals and patients. 

5.2.  Collection of Information and Criteria for Obtaining Specimens

    The availability of properly trained and briefed personnel is 
an essential element in the conduct of a study.  The investigating 
team will have to obtain detailed data on the disease 
characteristics and must include adequately trained clinical staff.  
The help and cooperation of international agencies and other 
departments within the country, or in other countries, may be
a A determinant is any factor, whether event, characteristic, or 
  other definable entity, that brings about change in a health 
  condition, or other defined characteristic (Last, ed., 1983).  
  The same source recognizes predisposing factors (e.g., age, sex, 
  occupation), enabling factors (e.g., climate, income), 
  precipitating factors (e.g., exposure to noxious agents), and 
  reinforcing factors (e.g., repeated exposures) in causation of 

needed, but the investigating team should comprise local 
investigators, as a cultural and language identity with the 
populations being investigated is essential.  When possible, the 
laboratory worker who will analyse the samples should participate, 
otherwise this team should receive adequate briefing from the 
responsible laboratory regarding the type and amount of samples to 
be collected, method of storage, transport, etc.  In particular, a 
statistician should be consulted regarding the size of population 
to be studied, when dealing with epidemiological studies of chronic 
diseases.  In the absence of ideally trained personnel in the 
investigating team, efforts should be made to brief and train 
available people appropriately. 

    A wide range of specific information should be collected in 
order to identify, as far as possible, all the relevant factors 
common to the identified cases.  Examples of such factors are given 
in Table 1.  Another possibility could be the use of the 
classification proposed by Last (1983) with an identification of 
the predisposing, enabling, precipitating, and reinforcing factors.  
However, situations will differ, and some of the items listed may 
not apply in certain situations. 

Table 1.  Factors to be considered during an epidemiological
investigation of an unknown disease
(a)   Factors relating to the physical environment

     Geographical location, including altitude, nature of terrain, 
     distance to rivers, lakes, swamps
     Climatic conditions
     Seasonal occurrence of symptoms

(b)   Man-made environmental factors

     Food preparation, cooking, and eating habits; storage 
     Water supply, sanitation
     Agricultural practices, including the use of fertilizers and 
     Industrial environment, including mining

(c)   Factors relating to the affected subjects

     Age distribution
     Sex distribution
     Family aggregation of cases and family structure
     Social and cultural factors: ethnic groups, religion, 
     education, etc.
     Socio-economic status, including income level
     Mobility of the population, migration
     Duration of residence in the area
 Note:  Recent changes concerning any of these factors should be 
       carefully documented.

    Background information on general health statistics should be 
collected through government/municipal/county/hospital/primary 
health centres, together with the following items:  morbidity, 
mortality, case fatality rates, and the trends in these indicators.  
Special attention should be paid to the possible occurrence in the 
past, or in nearby areas, of similar outbreaks, or even sporadic 
cases, constituting the unusual clinical entity. 

    Information on the environment must include recent changes in 
the environment if any, such as the destruction of forests, 
building of dams, opening of new industries, discharge of 
effluents, new range of products, or change in manufacturing 
processes.  The agro-ecological factors include the introduction of 
new varieties of food grain, mechanization of agriculture, use of 
agrochemicals, storage practices of harvested food, changes in the 
cultivation pattern, etc. 

    A co-existence between a disease in human beings and a similar 
disease in animal species provided important clues in some of the 
earlier studies of diseases later identified as being caused by 
exposure to chemicals in the environment.  Examples of these 
studies are those on Minamata disease (WHO, 1977), veno-occlusive 
disease (Tandon & Tandon, 1975; Tandon et al., 1976), and the 
aflatoxin outbreak in India (Tandon et al., 1977, 1978a).  
Information from farmers or veterinary officials on the outbreak or 
occurrence of related diseases in farm and domestic animals or 
other fauna and flora may yield valuable data. 

    Various additional sources can be used in the collection of 
relevant information.  The most useful information would generally 
come from the members of the affected community themselves.  
Further sources of information include community elders, social 
workers, and health personnel, including primary health and 
paramedical workers, general practitioners, and practitioners of 
traditional medicine.  Attention must also be paid to additional 
factors.  Thus, a family member or a member of the affected 
community may have very specific useful information such as 
practices in food storage or the special use of pesticides.  Some 
data could be collected through formal questionnaires for the 
village (unit) level, family level, or individual level.  Other 
methods could include less-structured personal interviews.  Some 
useful information may already be recorded elsewhere, for instance 
demographic characteristics. 

    An intensive or extensive sampling strategy should be designed, 
depending on a balanced trade-off between what would be desirable 
and what is feasible.  The specimens to be sampled should include 
biological samples, as well as samples of food, air, water, and 
other commodities.  In the absence of precise knowledge of the 
possible etiological factor and particular source, a large number 
of samples covering a wide range should be collected, the sample 
size being adequate for a reasonable range of analyses.  The range 
of sampling to be carried out should be decided on after generating 
a tentative hypothesis on the possible etiological factors, based 
on previously collected information.  However, even if a precise 

hypothesis has not been defined, potentially useful samples must be 
obtained as early as possible.  The samples should preferably be 
representative of the index cases, and sampling could be restricted 
to the families or individuals with the most typical case history.  
The samples should be obtained from both affected and non-affected 

    For practical purposes, there are limitations to the number of 
samples that can be collected and processed.  For this reason, some 
judgement must be made as to what would represent the most useful 
samples.  Such decisions are influenced by the time that has 
elapsed between the onset of the illness and the beginning of the 
investigation, the pertinence of the samples, and the possible 
routes of exposure.  For instance, if a food commodity is suspected 
in acute outbreaks, the food that was consumed immediately prior to 
onset of illness would represent the most valuable samples. 
Collection of the cooked food actually consumed is emphasized. 
Samples can also be collected from the food grains and the cooking 
medium from both local and commercial stores.  Identifying 
pertinent exposure to environmental sources may be more difficult 
in the case of chronic illnesses, as such exposures may have 
occurred some time in the past or may have varied over time. 

    There is a danger that samples might be contaminated, 
destroyed, or damaged during storage or transit.  Biological 
samples should be properly preserved in formalin or in an insulated 
container with ice or dry ice.  Agricultural commodities should be 
adequately dried before transporting.  These requirements must be 
agreed on with the analytical laboratory. 

5.3.  In-Depth Study of Cases

    The result of the initial investigation is the identification 
of one or several factors that are common to all identified cases 
of the disease or seem to be related to its distribution in the 
community.  An in-depth study of the outbreak/occurrence of cases 
requires that population-based studies, aimed at identifying the 
determinants of the disease, should be complemented with case-
control studies.  In the case-control design, cases of the disease 
are matched to a similar number of controls (people with no 
symptoms of the disease), in order to test the strength of the 
association between the exposure to the suspected etiological 
conditions and the occurrence of the disease.  The relative risk 
associated with exposure can be calculated on the basis of such 
studies (section 5.4). 

    Once the situation has been evaluated in the field, a special 
subgroup of the diseased population can be selected, unless only a 
small group of people have been affected, and studied in depth 
as a supplement to more formal epidemiologically designed 
investigations.  Such studies include detailed background 
questionnaires, medical examination, and relevant laboratory tests.  
The type of information to be collected will depend on the 
situation.  It is important to be as concise as possible and not to 
obtain a great deal of extraneous information, as this will only 
impede analysis of the data (see also sections 5.2 and 6). 

    The selection of cases for detailed investigation will depend 
greatly on the specific factors involved in the particular 
outbreak.  The following factors deserve consideration.  The most 
typical cases should be included.  If more than one member of a 
family is affected and a common factor among families is sought, 
then it may suffice to examine only one member per family.  
However, if the family is to be characterized, all members of the 
family should be examined.  It might be useful to confine the 
examination to children or other specific segments of the 
population.  In other situations, a common factor might be sought 
in individuals belonging to diverse subpopulations.  Cases that 
suddenly develop in another geographical area may be useful in 
identifying a common factor.  Alternatively, random sampling can be 
used to obtain representative samples for the epidemiological 

    Having dealt with the more readily available information in an 
acute outbreak of disease, additional studies should then be 
contemplated, such as more detailed morphological examination of 
affected target organs, and chemical analysis of biological fluids 
and tissue samples.  In addition to the fixation of tissues for 
morphological studies, selected tissues and biological fluids 
should be frozen for possible chemical analysis, only after 
obtaining initial clues suggesting a possible toxic agent.  For the 
successful identification of an etiological agent, it is important 
that the potential source of the toxic agent is identified and the 
exposure established through analysis of the incriminating 
material, such as food, or of body tissues and fluids.  The samples 
of such tissues and fluids, as well as of the incriminating 
material have to be properly collected and preserved following the 
advice of the analytical laboratory.  In the absence of specific 
information to the contrary, freezing at the lowest possible 
temperature is the best method of preservation.  Individual samples 
should be identified and stored separately, and pooling or mixing 
of samples should be avoided.  However, discretion in using this 
approach is advised, since extensive analysis is laborious and will 
rapidly deplete the supply of available samples. 

5.4.  Evaluation of Epidemiological Data

    The data collected must be analysed for the existence of dose-
response and dose-effect relationships and for the occurrence of 
specific differences between affected and comparable unaffected 
individuals.  Although results obtained should preferably be 
representative for the population examined, it may not be possible 
to meet this criterion very rigidly in studies of acute outbreaks.  
Appropriate reservations as to the general validity of such results 
must then be made.  In some outbreaks of acute poisoning, the 
illness experienced and the development of the epidemic may be so 
specific that it may not be feasible or necessary to apply a 
statistical approach.  A statistically significant result may only 
indicate a "spurious" association occurring by chance, and a non-
significant association could be due to an insufficient number of 
observations, lack of precision in the measurements performed, and 
other factors. 

    The information obtained must be carefully scrutinized for the 
presence of bias.  For example, bias in selection may be of 
importance if only the most severely affected patients are examined 
and differ in some important aspects from the group of patients as 
a whole.  Ascertainment bias may occur if a local informant is 
particularly aware of, and reports, cases.  Reporting bias in 
information may occur if prior information about the disease in the 
news media influences answers to questionnaires.  Errors may occur 
in many situations, if samples are mislabelled or if artifacts are 
introduced.  Confounding is likely to pose a problem, especially in 
studies of multifactorial diseases. 

    Epidemiological data can be analysed using the case-control 
approach and the follow-up approach (WHO, 1983).  In both 
approaches, control groups need to be selected.  In the first 
approach, the controls are people without signs and symptoms of the 
disease; in the other approach, the controls are those who have not 
been exposed to the chemical suspected of causing the disease. 

    In the study of acute outbreaks of unknown etiology, it is 
usually not feasible to select proper control groups, as the 
healthy people in the affected area may also be exposed, but to a 
lesser extent, and usually the causative agent has not been 
identified at this stage.  The usual procedure is to select as a 
comparison group, people who do not present signs and symptoms 
characteristic of the disease, or who appear not to have been 
exposed to the suspected agent.  In fact, these comparison groups 
are never fully comparable to the group under study and it should 
be emphasized that the absence of valid comparison groups may 
severely hamper the value of the study.  Although, during 
outbreaks, it may not be possible to identify valid comparison 
groups, tentative conclusions must be drawn on the basis of a 
critical assessment of all available data by the observer.  On the 
other hand, when dealing with endemic disease, it should be 
possible to select proper comparison groups controlled for specific 
suspected determinants on a prospective basis. 


6.1.  Experimental Animal Studies

    Animal studies are being used to complement investigations of 
outbreaks of disease and of endemic diseases of suspected chemical 
etiology.  The principal aim of these studies is to assist in the 
identification of the toxic substance and also to clarify the 
mechanism of action of the substance, after it is identified, and 
to develop an animal model for further study of the disease. 

    When a possible route of entry of the toxic agent is suspected, 
the material can be administered to animals by this route to see 
whether or not an illness is produced.  The animal model developed 
should reproduce the pathological features of the disease closely 
similar to those in human beings, and attention should be given to 
the target organ and types of cells involved (e.g., neurons, 
chondrocytes, etc.), the presence of storage materials in tissue or 
inclusion bodies, and the types of cellular reaction in the injured 
tissues.  It may not be possible to reproduce the exact clinical 
disease in animals, because the species chosen for study may simply 
not react to the toxic agent in exactly the same way as a human 
being.  Alternative species may be more or less sensitive to the 
offending agent, or the target organs may vary in different 
species.  Therefore, toxicological testing should preferably be 
done using a species in which a disease similar to that encountered 
in human beings has been observed in the field.  At times, it may 
not be possible to develop an animal model by simple exposure to 
the suspect chemical, since the disorder may be multifactorial, and 
simultaneous exposure to other environmental factors may be 
necessary to develop a syndrome comparable to the human disease.  
Such factors could include:  concurrent infectious disease, 
nutritional deficiencies, and mixed chemical exposures.  For 
instance, in encephalitis associated with the oral intake of 
bismuth salts, it was impossible to reproduce the disease in any 
animal species, in spite of the fact that the role of this compound 
in human disease had been established (Martin-Bouyer, 1981). 

    As mentioned, human beings may be more or less susceptible to 
the chemical than animals.  Nevertheless, the dose-response 
relationship is an essential consideration in the design of an 
experimental study.  The study should be designed to determine the 
minimal toxic dose, whether the toxic chemical may be accumulated, 
and if there is a time lag between the exposure and the effect.  
For instance, in the methylmercury outbreak in Iraq, loaves of 
bread containing the toxic substance were fed to domestic animals, 
but time was not allowed for the toxic effects to become manifest 
(latency period), resulting in the false interpretation that the 
bread was not toxic (Bakir et al., 1973; WHO, 1977).  Also, if the 
material fed to animals is a foodstuff, it must be ascertained that 
a caloric or nutritional imbalance or deficiency is not produced, 
resulting in disease symptoms not related to the toxic material. 

    Animal studies can provide information on the development of 
characteristic pathological changes produced in the affected organs 
by the chemical suspected of being involved in the etiology of the 
disease.  They can also help to identify factors influencing 
susceptibility to this compound.  When the possibility cannot be 
excluded that the etiology concerns exposure to a complex mixture, 
or is otherwise multifactorial, it would be misleading to base the 
evaluation only on the results of tests for the effects of exposure 
to a single compound. 

    Studies on biochemical effects should be designed and 
interpreted with cautious consideration of other measures of 
toxicity.  Studies of the metabolism and toxicokinetics of a 
putative chemical agent in animal models can provide information, 
important for planning and for the interpretation of results of 
screening and of analysis of biological specimens for toxic 
substances and their metabolites.  Such information includes 
identification of metabolites, determination of excretory rates, 
and elimination half-times of the chemical agent and its 
metabolites.  Principles of toxicological investigations and 
toxicokinetic studies are dealt with in detail in previous EHC 

6.2.  Analysis for Toxic Substances

    Analytical chemistry is important in investigations of endemic 
disease or of acute and chronic poisoning episodes in order to 
identify and quantify the toxic chemical within the environment and 
in affected persons.  It is desirable to quantify the offending 
agent in tissue samples to identify and, if possible, quantify, new 
exposure and to determine a dose-response relationship.  However, 
analytical methods with appropriate sensitivity and precision may 
not be accessible within the area of disease outbreak.  
Furthermore, some chemicals are rapidly metabolized and excreted 
making their detection in body fluids and tissue samples difficult, 
or even impossible.  Thus, the time between exposure and the 
collection of human specimens may be crucial, not only for the 
detection of the responsible chemical(s) and metabolites, but also 
for estimating the dose associated with the observed effects. 

    Analysis for microbial toxins represents a special problem.  
Intoxications caused by microbial toxins are mainly foodborne, but 
respiratory exposure has also been known in the case of fungal and 
algal toxins.  Microbiological investigation of suspected foods can 
be an important step in the identification of the chemical 
involved, indicating the chemical method of analysis to be applied 
for unequivocal identification of the causative agent.  Thus, if 
 Staphylococcus aureus is the predominant member of the microflora 
in foods that have been associated with an acute gastrointestinal 
disorder, then the food should be analysed for  Staphylococcus  
enterotoxins.  Identification of  Aspergillus flavus growing in 
foods (cereals, oil seeds), associated with acute hepatitis, may 
suggest analysis for aflatoxin B1, B2, G1, and G2 (WHO, 1979b). 
Routine methods are not available for the chemical analysis of some 
microbial toxins.  Identification and quantification can then be 

achieved through bioassays, though the analytical power is 
drastically reduced compared with chemical methods.  Thus, exposure 
conditions during outbreaks of paralytic shellfish poisoning (PSP) 
are estimated on the basis of a standardized mouse assay (WHO, 
1984b; AOAC, 1980).  However, chemical procedures for the 
determination of paralytic shellfish poisoning components, such as 
high-pressure liquid chromatography, are available and may soon 
replace a bioassay. 

6.3.  Toxic Chemical Information Data Systems

    Most data systems are based on studies exploring toxic effects 
produced by exposure to known, specific chemicals, plants or their 
extracts, natural toxins, etc.  In other words, these systems are 
developed under circumstances in which the agent is known.  When a 
disease is the starting point of investigation, the signs and 
symptoms are known, but the chemical is unknown or only suspected.  
A number of existing data systems listing the toxic effects of 
chemicals are computerized.  These systems can be used by 
professional information specialists to list all chemicals reported 
to produce a specific effect, e.g., neurotoxic effects.  However, 
the process of establishing diagnostic criteria involves knowledge 
of the relative specificity of various signs and symptoms as well 
as of the order of their appearance.  Because of this, relevant 
information from such existing systems can be obtained through the 
interaction of a professional information specialist with a 
specialist of a suitable medical background. 

    A source would be useful, providing information on specific 
requirements for the collection of biological specimens, the types 
of specimens to be collected, the amount of sample needed for 
chemical analysis, means of preservation of the specimens, as well 
as a directory of laboratories performing specialized analyses. 


7.1.  Causation in Human Disease

    Human disease occurs as a result of a series of events, 
beginning with some initial insult or insults, which then develop 
further.  The final manifestation of disease may be the result of 
various promoting, modulating, or interfering factors related to a 
number of factors including genetic make-up, nutrition, life style, 
and environment.  In some situations, a specific disease simply 
seems to develop as a direct result of a particular factor, i.e., a 
monocausal relationship.  However, frequently, more than one factor 
may be involved in the evolution of the disease.  Also, several 
conditions or characteristics may be associated with the occurrence 
of the disease, without necessarily being causally related.  Thus, 
in the search for the chemical etiology of a human disease, 
specific causal factors that constitute necessary (though rarely 
sufficient) conditions for the development of the disease need to 
be identified.  When searching for these causal factors, case 
definitions and diagnostic criteria must adequately distinguish the 
particular disease under investigation from similar conditions with 
different etiologies.  However, the disease should not be separated 
into too many subentities as this blurs the impression of a common 
causation.  Individual disease entities frequently have a 
heterogeneous etiology, as in the case of end-stage kidney disease 
or organic brain dysfunction.  Some diseases are called 
"idiopathic" or "essential", their causes being unknown, and 
eponyms and pathological features are frequently the basis for 
names of diseases or their classification.  The same chemically-
induced liver disease has even been given different names in 
independent outbreaks, viz., "hepatitis with ascites" (Dubrovinski, 
1952) and "veno-occlusive liver disease" (Tandon & Tandon, 1975).  
It may be difficult to determine whether an outbreak of a disease 
is new or, if similar outbreaks have occurred in the past, whether 
the etiology has, perhaps, already been elucidated. 

    In the investigation of disease outbreaks or endemic disease, 
the analysis must first of all focus on the clinical and 
epidemiological features of the disease.  Pathology, toxicology, 
and other related disciplines provide further information.  
Detailed analysis of the clinical manifestations and morphological 
changes in organs may at times help to identify etiological agents 
(Parish et al., 1979; Cooper & Kimbrough, 1980).  On the other 
hand, some chemicals that cause acute poisoning and death may show 
few, if any, morphological changes in organs or only very non-
specific changes (Diggory et al., 1977).  Several compounds produce 
morphological changes that can be considered characteristic, even 
if not necessarily specific for one compound, e.g., status 
spongiosus of the white matter of the nervous system, which is 
observed after exposure to hexachlorophene or triasultane 
(Kimbrough, 1976).  In the same way, some biochemical alterations 
can be considered characteristic, such as the inhibition of 
cholinesterase by organophosphorus compounds (Wills, 1972), or the 
inhibition of uroporphyrinogen decarboxylase in the liver by 
hexachlorobenzene, resulting in acquired porphyria cutanea tarda 

(Cam & Nigogosyan, 1963; Taljaard et al., 1971; Felsher et al., 
1982).  However, the circumstances of the events leading to the 
illness need to be investigated in detail, since the nosographic 
specificity may not allow proper judgement without supporting 

    For many chronic diseases, the situation is more difficult.  A 
chronic disorder could result from an acute insult, such as the 
permanent paralysis caused by triorthocresyl phosphate (Morgan & 
Penovich, 1978), or the onset may be insidious resulting from a 
cumulative effect following repeated insults, such as the 
development of emphysema after years of smoking.  Finally, a 
disease may have a composite etiology, such as glucose-6-phosphate 
dehydrogenase-associated anaemia, which is caused by a combination 
of genetic abnormality and an environmental chemical. 

    An individual disease is recognized by its characteristic 
combination of symptoms and signs.  Each component may not 
necessarily be pathognomonic, but the association between otherwise 
non-specific symptoms and signs may constitute a typical 
appearance.  For example, Thomas Addison, in the 19th century, 
first described pernicious anaemia by separating it from general 
anaemia, since it occurred without any discoverable cause, such as 
loss of blood or malignant disease.  In the case of pernicious 
anaemia, the absence of other signs present in previously 
established forms of anaemia, was a surprising observation.  
Subsequently, the discovery of vitamin B12 and the mechanism of its 
absorption in the gut was discovered.  Research on several other 
diseases has followed a similar line. 

    In approaching the etiology of a "new" disease, a step-wise 
series of considerations may be useful, starting from more general 
criteria and concluding with a detailed evaluation of the strength 
of the accumulated evidence.  The initial steps are particularly 
useful, when considering strategies to elucidate an outbreak of a 
new disease, while the final evaluation of the data is similar to 
criteria generally used when considering causal links. 

    If a disease occurs in a particular environmental setting, this 
should be characterized with regard to a set of factors, discussed 
in section 5.2 and summarized in Table 1.  Genetic disease should 
be considered.  The following considerations may be useful with 
regard to inherited diseases:  (a) occurrence of the disease in 
definite proportions among persons related by descent; (b) failure 
of the disease to appear in unrelated lines (e.g., spouses, in-
laws); (c) characteristic age of onset and course, in the absence 
of known precipitating factors; (d) greater concordance of 
incidence in monozygotic than in dizygotic twins.  Furthermore, a 
genetic component may be indicated by studies of genetic isolates 
or races, more detailed examination of clustering within families, 
relationship to blood types, and occurrence of characteristic 
chromosomal anomalies (Murphy, 1972).  Many diseases have a genetic 
component that may determine individual susceptibility (Kimbrough, 
1984).  Also, some forms of inherited or inborn disease are not 
expressed, unless an individual is exposed to environmental 

chemicals or drugs, e.g., with atypical plasma-cholinesterase 
(Baker et al., 1977) or deficient glucose-6-phosphate dehydrogenase 

    In the case of environmentally-related disease, individuals who 
move into the environmental setting run a risk of developing the 
disease, while individuals who leave will normally not suffer 
further deterioration and may even recover. 

    If an acute illness of unknown etiology is encountered, both 
infectious and chemical causes should be considered.  Principal 
investigations into the causes of the disease should be governed by 
the most likely etiology.  However, other possible causes 
(infectious versus chemical, versus multi-factorial) should not be 
ignored.  Koch's postulates, which were developed to elucidate 
microbial infections, rarely if ever apply to chemical-induced 

7.2.  Consideration of a Chemical Etiology

    The distinction between chemical and infectious etiology is of 
special importance when considering the possible strategies for 
prevention.  In this regard, two main sets of data should be 
considered, i.e., clinical symptoms and epidemiological 
characteristics.  In addition, the results of laboratory 
investigations and experimental animal studies may further 
elucidate the question, if supplementary evidence is needed. 

    In considering clinical patterns, sudden deaths early in the 
outbreak after a prodromal period of a few hours would suggest a 
chemical etiology.  Non-pathognomonic individual signs and symptoms 
taken alone are of little value in distinguishing between poisoning 
and infection.  Thus, although it is not a common feature of 
diseases caused by chemicals, fever may be seen with compounds that 
uncouple oxidative phosphorylation, or otherwise impair temperature 
regulation.  Examples of such compounds are:  pentachlorophenol 
(Robson et al., 1969), dicoumarol (Toolis et al., 1981), 
hexachlorophene (Martin-Bouyer et al., 1982), and aflatoxin (Ngindu 
et al., 1982).  Sudden enlargement of lymph nodes, increased 
peripheral white cell counts, persistent diarrhoea after "cessation 
of exposure", and early acute inflammatory exudates are usually not 
part of the clinical picture of a chemical poisoning.  On the other 
hand, in metal fume fever, both fever and increased white cell 
counts are seen (Parke, 1982).  Thus, the total clinical picture 
should be considered.  Moreover, chemicals may modulate the 
function of the immune system or otherwise increase individual 
susceptibility to infection.  In this case, infection would be seen 
as pre-disposed by chemical exposure. 

    Consideration of the following epidemiological features may be 
helpful when investigating the etiology of a disease not previously 

    (a)  case-to-case transmission of the disease (presence or
         absence of secondary cases);

    (b)  common source of exposure;

    (c)  have all patients received the same dose of the chemical;

    (d)  geographical distribution of cases within well-defined 
         areas; and 

    (e)  distribution within particular age groups, sex, 
         socioeconomic strata, and other demographic subgroups. 

    Early in an outbreak, it is often difficult to identify 
features characteristic of diseases caused by certain chemicals 
(e.g., hexachlorophene) or infectious agents (e.g., Legionnaire's 
disease).  The occurrence of secondary cases within a family, days 
to weeks later, might suggest an infectious agent.  If such 
secondary cases occur within several families at regular intervals, 
an infectious agent with an incubation period is suggested.  
However, no secondary cases were observed in, for example, 
Legionnaire's disease.  Therefore, it may not be possible, early in 
an outbreak, to determine whether a disease is infectious by nature 
or caused by a chemical, and both leads will have to be followed 
up.  As the epidemic progresses, this distinction is likely to 
become easier. 

7.3.  Temporal Relationships

    The temporal relationship between the disease and associated 
variables must be known in order to establish a causal 
relationship.  Thus, the time sequence is an important criterion in 
evaluating causality and should be considered early in the process. 

    Sometimes, specific events can be associated with the onset of 
illness, such as the change of a production process in a chemical 
factory, or the use of a new chemical in a commercial product, as 
in the case investigated by Mallov (1976) of methyl-isobutyl-ketone 
which was replaced by methyl- N-butyl ketone.  These and similar 
leads should be carefully investigated.  Though a time-relationship 
should be sought, the temporal association between cause and effect 
may not be very obvious and may follow an unpredictable pattern. 

    Exposure to the chemical factor must occur or begin prior to 
the development of disease.  In the case of acute toxicity, the 
adverse effects follow as an obvious consequence of the chemical 
exposure.  However, this sequence may frequently not be apparent.  
This is the case when exposures are long-term, irregular, or mixed.  
Some chemicals are rapidly metabolized and excreted, thus 
disappearing from the body shortly after exposure.  In other cases, 
the chemical is accumulated in the body, and may remain in body 
depots for decades, perhaps resulting in disease much later than 
the initial exposure.  This sequence would depend on dose and on 
individual susceptibility.  Also, when the effect is non-specific, 
develops insidiously or is delayed, the time of onset of the 
disease may not be well defined.  In addition, the expression of 
disease may be determined by a factor independent of the chemical 

    A chemical may cause an acute illness from which the patient 
appears to recover only to develop a permanent injury after a delay 
of several days to weeks, as in the case of neuropathy after 
triorthocresyl phosphate intoxication (Morgan & Penovich, 1978) or 
the development of cataracts following ingestion of dinitrophenol 
(Horner et al., 1985).  Continuous internal exposure to, e.g., 
persistent chemicals or asbestos fibres, may ultimately lead to 
disease.  Certain diseases, such as cancer or lung fibrosis, may 
continue to progress, even after the exposure has long ceased. 

7.4.  Biological Plausibility

    While specific chemical etiology may be suggested by the 
clinical and epidemiological features, additional leads can be 
obtained from detailed examination of autopsy samples and clinical 
laboratory data including results of chemical analysis for toxic 
substances (section 6.2).  Once a chemical or a family of related 
chemicals is suspected in an environmentally-induced disease, the 
criterion of biological plausibility in establishing the role of 
the suspect agents as etiological factors in the disease has to be 
considered.  This criterion is important when investigating causal 
relationships.  However, in many cases, the toxicokinetics and/or 
biochemical mechanism of toxic action of a particular chemical are 
not known with certainty.  In such cases, it is more difficult to 
use biological plausibility as a criterion to determine the 
association between a given disease and a particular chemical 
agent.  Nevertheless, as toxicological investigations advance, the 
linkage of various metabolic effects with specific chemicals 
becomes possible and should be pursued.  When reviewing the toxic 
effects of chemicals, the extent to which the affected population 
could have had access to the substances under consideration should 
be determined.  Furthermore, if a suspect chemical compound is 
known to have, for instance, haemolytic effects, and the disease in 
question does not involve haemolysis, then this compound can 
effectively be ruled out as a causative factor in the disease.  On 
the other hand, if the suspect agent is known to inhibit or induce 
certain metabolic pathways or enzymatic reactions and these 
biochemical activities are depressed or activated in the disease 
concerned, then this can be taken as supportive evidence for a role 
of the chemical in the etiology of the disease. 

    When the effects of exposure to a chemical, found to be 
associated with the disease in question, do not fulfil the 
criterion of biological plausibility, the possibility should be 
explored of contamination of the chemical with a more toxic 
substance.  The purity of manufactured chemicals may vary and they 
can occasionally contain trace amounts of highly toxic 
contaminants.  Furthermore, exposures to such mixtures may result 
in additive, synergistic, potentiating, or antagonistic effects.  
If only exposure to the technical grade or less than pure compound 
is identified, it may be difficult to explain the illness observed, 
as in the case of Yusho disease, where the clinical manifestations 
greatly exceeded the severity expected from polychlorinated 
biphenyl exposure alone, but would be explained by the presence of 
trace amounts of polychlorinated dibenzofurans (Masuda & Yoshimura,
1984).  In such situations, it may therefore be useful to evaluate 
the production process of the chemical involved and to determine 
the extent to which toxic impurities are present (Baker et al., 

    Toxic impurities may also develop on storage at high 
environmental temperatures, or because of exposure to sunlight. 
Furthermore, human beings may be exposed simultaneously to more 
than one chemical, resulting in possible interactions. 

    From the examples presented above, it should be clear that both 
pathophysiological and biochemical alterations can be used to 
establish whether or not the suspect agent satisfies the criterion 
of biological plausibility.  If the criterion cannot be met at an 
early point in the investigations, a re-evaluation should be made, 
when more information has been obtained. 

7.5.  Dose-Response and Dose-Effect Relationships

    If possible, the search for, and confirmation of, chemical 
etiologies for specific diseases should include studies on 
relationships between the incidence and severity of the particular 
disease and the intensity and duration of exposure to the factor or 
factors suspected of causing the disease.  However, a simple 
relationship between "dose" and disease outcome may not necessarily 
be apparent. 

    In outbreaks of acute poisoning, the severity of the clinical 
manifestations will generally depend on the dose of the chemical.  
For instance, food may be contaminated, but the level of 
contamination and individual intake may not be uniform.  Some 
people ingesting much of the food item may receive a high dose and 
others a much lower dose.  Therefore, some of the exposed may 
develop severe disease, while others may only develop a few of the 
symptoms and signs related to the disease, or none at all.  For 
some diseases, a quantal relationship exists where the same type of 
exposure will result either in a certain type of disease or in no 
obvious ill effects.  Different segments of the population may vary 
in their susceptibility to toxic effects.  Depending on the dose, 
the effects may be acute, following one-time inhalation, ingestion, 
or dermal exposure to a toxic quantity of a substance.  However, at 
very low doses, a single dose may not result in any illness, 
particularly for chemicals that are cumulative.  Thus, the 
integrated exposure over a long period, as reflected by the build-
up of the chemical in the body, should be taken into account in 
dose-effect, dose-response considerations.  Such long-term exposure 
levels should be compared to general background levels, and, if 
possible, properly selected control areas should be examined as a 

    From results in experimental toxicology, it is known that many 
chemicals affect cellular and subcellular systems before overt 
disease occurs.  Some such effects can be quantified using non-
invasive techniques or by analysing a blood samples.  The clinical 
significance of many of these tests is not clear at the moment, and 

they need to be validated further.  On the other hand, some of 
these tests, for example the determination of red blood cell-
cholinesterase and, within certain risk groups, determination of 
urinary-beta-microglobulin excretion, have become useful markers of 
chemical exposure, and/or effects, and have been used for dose-
effect and dose-response evaluations. 

7.6.  Effects of Intervention

    There are two types of intervention.  Primary intervention 
involves efforts to prevent continued exposure to the offending 
environmental factor, while secondary intervention prevents or 
ameliorates the damage caused by the exposure.  Distinguishing 
between these two categories may not always be straightforward, 
particularly when the pathogenesis of the disease is not known.  
However, if adequate prevention can be achieved by secondary 
intervention, the search for specific chemical etiology becomes 
less urgent. 

    As soon as a chemical etiology has been suggested, primary 
intervention should be considered to prevent further occurrence of 
new cases or progression of the disease.  Through this approach, 
further proof of a causal relationship can frequently be obtained.  
The results of a preliminary intervention will frequently give 
rise to subsequent, more specific interventions that may further 
support the causal relationship.  Efforts in this area should 
preferably include a control group, and the effects of the 
intervention must be separated from the natural cycles of the 
disease and the effects of other environmental factors.  For 
example, outbreaks of disease of chemical origin may be self-
limiting.  The question of whether intervention occurred when the 
number of cases was still increasing or whether they were already 
decreasing at this time may be crucial.  Examples of intervention 
include the removal of contaminated food items from circulation and 
the warning of the population against hazards, such as not to 
consume grain treated with fungicide.  Every effort should always 
be made to identify and conduct intervention measures, in order to 
augment disease prevention. 

7.7.  Confirmation of a Causal Relationship

    After an association between a particular chemical and the 
disease has been identified, the validity of the association should 
be confirmed.  The causal relationship could be supported, for 
instance, through the detection of the toxic chemical or its 
metabolites in tissues or biological fluids, or through laboratory 
studies on appropriate experimental species, though, as discussed 
in section 6, an animal model may not be readily identified.  
Information on adverse effects in wild or domestic animals exposed 
to the chemical factor may be useful in this regard.  For example, 
for confirmation of the involvement of aflatoxins in human 
aflatoxic hepatitis, the contaminated corn grains consumed by 
affected individuals were fed to ducklings, which then developed 
bile-duct proliferation in the liver, which was typical of 
aflatoxicosis (Krishnamachari et al., 1975). 

    Another means of confirmation is to relate the type, levels, 
and extent of exposure to the chemical with previous or subsequent 
disease outbreaks in human beings, if any.  For example, the 
clinical symptoms, levels of aflatoxins in the staple food, and 
conditions of exposure during the outbreak of aflatoxic hepatitis 
in Kenya were similar to those reported earlier from India.  
Similarly, conditions related to veno-occlusive disease in India 
associated with pyrrolizidine alkaloid contamination of food grains 
were similar to those that caused the disease in Afghanistan.  
Furthermore, the cause of endemically-occurring osteosclerosis was 
discovered when a similar disease, skeletal fluorosis, was 
described in workers exposed to excess levels of fluoride. 

    Ideally, when considering the association between the suspected 
causal factor and the resulting disease, the overall evidence 
accumulated should be critically reviewed, according to the 
following established criteria discussed in detail by Susser (1973) 
and Lilienfeld & Lilienfeld (1980): 

    (a)  consistency of association, i.e., the repeated
         observation of the connection between chemical
         exposure and effects, under different circumstances;

    (b)  strength of association, i.e., more intense exposure
         leads to more frequent or more severe effects;

    (c)  specificity of association, i.e., similar signs and
         symptoms are not observed in the absence of the
         suspected agent.

    The criteria of time sequence and of coherence (biological 
plausibility) and also of dose-response relationship were dealt 
with in previous sections (7.3, 7.4, and 7.5, respectively). 
However, all these criteria may sometimes be difficult to apply in 
practice.  Outbreaks of poisoning may be isolated events, and 
idiosyncratic reactions or individual susceptibility may blur the 
relationship to dosage levels.  With chronic disease, where 
chemical exposure constitutes only one of the risk factors, the 
evaluation of the significance of a particular chemical exposure is 
more difficult. 


    Appropriate preventive measures must be implemented as soon as 
is possible and feasible after the nature of the chemical agent, 
the pathway of exposure, and the source have been identified. 

    Having determined the magnitude of the hazard in terms of the 
size of population affected and the geographical areas involved, 
the following public health measures should be undertaken in 
addition to the obvious measures for the treatment and 
rehabilitation of patients. 

8.1.  Preventive Action and Control

    Strategies have to be planned for:  (a) immediate steps to 
control the outbreak; and (b) prevention of such outbreaks in the 
future.  Many of these steps have multisectorial implications and 
need coordinated and integrated approaches for their success.  
Immediate preventive measures depend on the type of chemical 
involved and the pathway of exposure.  If the contamination is 
through food, steps have to be taken to seize and destroy the 
damaged or contaminated food grain or food material, to prevent the 
community from consuming such food, and alternative sources of food 
must be made available.  Wherever possible, the commodity should be 
retrieved by cleaning or detoxifying under supervision.  After 
identifying the chemical(s) involved and their source, it may be 
possible to prevent the entry of the chemical(s) into the food 
chain.  For example, recognition that pyrrolizidine alkaloids 
contaminated food through the seeds of certain plants made it 
possible to eradicate veno-occlusive disease by introducing simple 
preventive measures, and removing the incriminating seeds from the 
grain (Tandon & Tandon, 1975). 

8.2.  Surveillance and Monitoring System

    A surveillance system should be established or strengthened in 
all cases of chemically-induced disease, and should be suitably 
designed according to the nature of the exposure.  If the chemical 
is identified and can be removed from the environment, apart from 
monitoring for its recurrence in the environment, a long-term 
follow-up, especially of the persons affected by the disease, may 
be necessary.  This is especially important if, according to known 
experimental or human data, some health effects could manifest 
after a period of time.  This is of particular relevance for 
carcinogenic effects.  Thus, the creation of long-term machinery is 
necessary for follow-up surveillance, including periodic physical 
examination of the affected cases and monitoring for the appearance 
of the earliest signs of the disease. 

    If the chemical has not been precisely identified, or if it 
cannot be removed from the human environment, the following 
surveillance measures are recommended: 

    (a)  to ensure the reliability of disease-specific morbidity 
         and mortality data; 

    (b)  to monitor the incidence, i.e., the occurrence of new

    (c)  to monitor changes in the distribution of the disease that 
         may indicate changes in exposures; 

    (d)  to monitor the evolution of disease symptoms and 
         complications to initiate rehabilitation programmes, when 

    (e)  to monitor specific environmental hazards, if identified.

    A formal registry of cases is a valuable tool.

8.3.  Health Education

    With the identification of the chemical etiology of a disease 
and the initiation of preventive steps, the need to disseminate the 
information to the professionals involved and to educate the public 
in appreciating the nature of the hazard, and ways and means of 
preventing and minimizing them, cannot be over-emphasized.  For 
this purpose, the role of the mass media is particularly important.  
To improve the preceptiveness of the medical and paramedical 
personnel for such information, the medical/nursing/paramedical 
curricula should include adequate sections on the role of chemicals 
in contributing to disease. 


9.1.  Cooperation and Collaboration among Countries

    Technical cooperation among countries is extremely important 

    (a)  The same diseases of suspected chemical etiology may be 
         found in several countries in different parts of the world 
         or in countries belonging to the same geographical area, 
         where the populations are exposed to the same 
         environmental hazards.  Thus, there is a need for the 
         sharing of knowledge by countries with experience of the 
         endemic disease and for cooperative efforts in the control 
         of common public health problems.  The relevant discussion 
         on Kashin-Beck disease can be found in Appendix III.

    (b)  There is a need for joint efforts in activities such as 
         the training of personnel, exchange of experts and 
         specialists, the use of sophisticated laboratory tests for 
         clinical diagnosis, and pathological and toxicological 

    (c)  It is essential that clinical, epidemiological, and public 
         health information and experiences should be shared to 
         develop surveillance and monitoring activities for common, 
         and newly emerging, problems. 

    (d)  Joint ventures in the field of research are necessary 
         concerning problems of common interest.  This can be 
         facilitated by the establishment of "Sister Institutions" 
         dealing with the same problem in different countries.

    (e)  Cooperation among countries makes it possible to carry out 
         more extensive investigative programmes on common health 
         problems, which would exceed resources available in one 
         country, and to develop and implement preventive measures 
         of benefit to all of them. 

    (f)  Mutual technical and economic assistance is needed in case 
         of disasters to deal with, and solve, emergency situations.

    All these aspects should be considered in the context of the 
social and economic development of the member countries, taking 
into account the need for a multisectorial approach in the 
prevention and control of diseases of chemical etiology. 

9.2.  Global and Regional Activities

    The disease-oriented approach, which has been used when 
establishing the role of certain chemicals in the etiology of 
outbreaks of locally endemic diseases, has provided a basis for the 
prevention and control of these diseases; thus, it must be 
recognized as an important component of chemical safety.  There is 
a need to strengthen methodological cooperation at both the global 

and regional levels, and the methodological component of the IPCS 
has a well-defined role in this respect.  It is also necessary to 
develop, through the IPCS, regional and global registries of 
endemic diseases with suspected chemical etiologies, to facilitate 
the harmonization of activities aimed at improved understanding of 
their causation, and at the prevention and control of these 

    Thus, at both global and regional levels, there is a need to: 

    (a)  Increase awareness of the potential of chemicals to induce 
         disease and of the need for international cooperation to 
         achieve the goal of chemical safety, including the 
         prevention and control of diseases of chemical etiology;

    (b)  Strengthen national capabilities in environmental
         epidemiology, toxicology, and related fields;

    (c)  Promote and coordinate relevant research activities;

    (d)  Develop guidelines on environmental epidemiology;

    (e)  Identify relevant institutions at the country level to 
         promote training and research in the field; 

    (f)  Apply health criteria in establishing national standards, 
         and in promoting the national regulations according to the 
         needs of the different countries and specific 
         epidemiological situations; 

    (g)  Promote the evaluation of existing control programmes;

    (h)  Develop new, and improve existing, indicators to be used 
         in the epidemiological investigation of outbreaks of 
         disease and chronic endemic diseases, and for the 
         evaluation of control measures; 

    (i)  Strengthen health monitoring and surveillance systems at 
         the country level; 

    (j)  Strengthen the infrastructure of health services to
         implement activities for the control of environmental
         hazards, and to create or improve the surveillance system, 
         the laboratory capabilities, and the research institutions;

    (k)  Help member countries to establish a set of priorities for 
         chemical hazards control action within the framework of 
         health for all by the year 2000 and its main strategy, 
         primary health care. 

9.3.  Final Recommendations

    In summary, the following three main recommendations should be 
implemented through the global, regional, and country levels: 

    -    to promote and stimulate the collaboration and cooperation 
         among member countries towards joint efforts for the 
         better knowledge and implementation of control measures in 
         common problems involving chemical safety;

    -    to accelerate and increase the training of specialized 
         personnel in the different regions and member countries;

    -    to promote and stimulate the collection and sharing of 
         clinical, epidemiological, and biological information 
         concerning outbreaks of disease and chronic endemic 
         diseases that are chemically-related. 


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AMIN-ZAKI, Professor L.
    A tale of two alkylmercury poisoning epidemics in Iraq

BABABUNMI, Professor E.A.
    (a) Possible involvement of Cassava in certain tropical
        endemic diseases
    (b) A biochemical approach for establishing the role of
        cyanide in the etiology of tropical ataxic neuropathy

    Endemic disease outbreaks in India due to chemical toxins

    The problem of chemical etiology of certain human diseases

    An outline of history of research on Kashin-Beck disease
    in Japan

    Identification of diseases caused by chemicals in the

    Constraints in establishing the etiology of environmentally-
    induced disease

    Biochemical criteria of environmentally-induced diseases

    Investigation of acute outbreaks of human illness caused
    by chemicals

KROGH, Professor P.
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    in human diseases caused by fungal and algal toxins

    Theories of nutritional deficiency in the etiology of
    endemic diseases

    Techniques for investigating the etiology of disease

    Thoughts on three epidemiological enquiries into
    collective accidents due to a poison

SHIBATA, Professor S.
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TANDON, Professor H.D.
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    and episodes or outbreaks of chemical poisoning with
    special emphasis on developing countries

YANAGAWA, Professor H. & SHIGEMATSU, Professor I.
    The epidemiological approach to the chemical etiology of
    specific diseases: Itai-itai disease, Minamata disease,
    and Yusho (PCB poisoning)



    This framework, originally presented at the Task Group meeting 
held in Beijing from 28 October to 8 November 1985, is based on 
experience during studies on the aflatoxin-induced outbreak in 
India (Tandon et al., 1977; WHO, 1979b) and the outbreaks of veno-
occlusive disease in Afghanistan (Tandon & Tandon, 1975; Tandon et 
al., 1978b) and India (Tandon et al., 1976).  It was amended at the 
editorial meeting held in Geneva from 28 April to 2 May 1986, to 
include as examples, studies in which a similar approach had been 
used when establishing the chemical etiology of disease outbreaks 
related to hexachlorophene (Martin-Bouyer et al., 1982) and 
dicoumarine (Martin-Bouyer, 1983). 


    To investigate the etiology of a disease, follow a "disease-
oriented" approach as opposed to the classical toxicological 
"substance-oriented" approach.  Recognition of the occurrence of an 
unusual disease is the initial requirement. 

    In order to be considered unusual, the disease entity may: 

    (a)  be characterized by pathognomonic signs that do not occur 
         in a known disease; 

    (b)  include non-specific clinical features, signs, and 
         symptoms and clinical laboratory and other data that do 
         not fit into a known disease category; 

    (c)  be present as a cluster of cases of a disease that 
         normally occurs with a lower frequency; or

    (d)  be present as an endemic disease of unknown etiology.

    The search for an etiology can be carried out in the following 
three phases. 


     After ascertaining that the disease is "unusual", the general 
features of the disease, the circumstances under which it occurs, 
and the size and nature of the population, or type of patients 
involved, can be studied.  The following steps are suggested: 

1.1  Development of a Case Definition

    For conducting an epidemiological study and to ensure the 
uniformity of collected data, guidelines for screening the 
population have to be developed.  Criteria are needed for two 
levels of screening, initial or mass screening and a later 
screening that requires diagnostic criteria to confirm the cases. 

1.1.1  Criteria for recognizing index cases during mass screening

    Criteria for the identification of index cases consist of major 
clinical signs and symptoms, for example: 

    (a)  acute jaundice in the aflatoxin outbreak;

    (b)  rapidly developing ascites in the outbreak caused by
         pyrrolizidine alkaloids;

    (c)  encephalitis with bullous dermatitis on buttocks in cases 
         of hexachlorophene toxicosis; and 

    (c)  haemorrhagic syndrome in newborn infants, without fever in 
         cases of dicoumarine poisoning. 

1.1.2  Criteria for confirming cases suspected in mass screening

    These may include a combination of:  symptoms, signs, laboratory 
data, X-rays, etc, and pathological features. 

    The criteria selected in the studies used as examples in this 
paper were: 

    (a)  characteristic morphological features observed in the 
         liver biopsies in cases of toxicosis due to aflatoxins and 
         pyrrolizidine alkaloids; 

    (b)  characteristic morphological lesion in the central nervous 
         system and presence of chemical in blood and bones at 
         autopsy, in cases of hexachlorophene poisoning; and

    (c)  bleeding diathesis consistent with avitaminosis K, in
         cases of dicoumarine poisoning.

1.2  Descriptive Pattern of the Disease

    This may include a study of the clinical features of the 
disease, the dominant signs and symptoms, the clinical course of 
the disease and, in case of an outbreak, an approximate idea of the 

size of the population affected, the mortality rates, etc.  Visits 
to the field or site of occurrence by the investigating team, which 
should include adequately trained clinical staff, are essential and 
cannot be over-emphasized.  Study of the habitat, and the family 
style of living, cooking, and eating, may provide crucial clues.  
The investigating team should mainly consist of persons with the 
same cultural background as the affected population, or at least 
persons familiar with it.  In addition, the following information 
can be obtained: 

    (a)  Cluster analysis of cases, either according to factors 
         related to the physical environment, e.g., geographical, 
         seasonal, or to factors related to affected subjects, 
         e.g., age, sex, family structure, socio-economic status, 

    (b)  Retrospective study of health statistics of the area,
         obtained through government, municipal, or county
         data, or from hospitals and other health-care facilities 
         in the region. 

    (c)  Pattern of illnesses in the affected area compared with 
         control area; 

    (d)  Study of the original source of food and of food storage 

    (e)  Identification of locally endemic diseases, if any.

    In the case of a disease outbreak, reports providing some of 
the above information and often important clues to the etiology of 
the disease, especially if a similar disease has been known to 
occur in the past, may be obtained from local general 
practitioners, primary health/paramedical workers, health 
officials, social workers, and school teachers. 

1.3  Study of Locally Prevalent Animal Diseases

    Unusual happenings, if any, should be noted in the fauna, farm 
animals, and domestic animals. 


    Having collected the descriptive data on the disease and the 
above information, there may be possible clues suggesting, at 
least, the nature of the likely etiological factor(s).  While 
generating a hypothesis, attention should be focused on the most 
typical cases.  The following steps are suggested: 

2.1  Examination of Diseased Tissue

    Examination of even one or two tissue specimens, especially the 
main diseased organ, may provide crucial clues to the etiology of 
the disease, particularly in the light of the descriptive pattern, 
in the initial phases of the study.  If available, the diseased 
tissue of both animals and patients should be examined. 

    For example, in the study on the aflatoxin-induced outbreak, 
the finding of syncitial giant cells in human liver tissue, 
identical to those found in rhesus monkeys administered aflatoxin, 
suggested mycotoxin etiology. 

2.2  Possible Clues in the Environment 

    The following factors should be investigated:

    (a)  Unusual happenings in the environment, e.g., drought,
         floods, heavier than normal rainfall, etc

    (b)  Opening of new industries, manufacture of new chemicals or 
         products using new chemicals, change in the manufacturing 

    (c)  The use of pesticides/fungicides

    (d)  Introduction of new seed/agricultural practices, involving 
         the use of a new chemical 

    (e)  Disposal of industrial waste

    (f)  House-keeping practices in the local industry

    (g)  Change in food habits

    (h)  Possible contamination of staple food/cooking medium

    (i)  The use of a new household chemical.

2.3  Consideration of Possible Routes of Exposure

    Exposure usually occurs orally or via inhalation.  However, the 
more unusual dermal route of exposure should also be considered. 


    On the basis of the above information, one or more etiological 
factors may be suspected and a hypothesis generated, which then has 
to be tested as described below: 

3.1  Exploration of Reports of Occurrence of Similar Episodes or 
Diseases Elsewhere in the World, Using Available Data Base Systems 

3.2  Evolution of a Strategy for Further Study, Taking Into Account 
the Specific Characteristics of the Suspected Agent 

    This step includes:

    (a)  Identification of specific biological markers of exposure 
         and of toxicity; 

    (b)  Listing of laboratory procedures/analyses to be carried 

         (i)   in the field;
         (ii)  in local institutions;
         (iii) at specialized laboratories;

    (c)  Establishment of range and type of epidemiological data to 
         be collected; 

    (d)  Decisions on type and expertise of specialized personnel 
         required to conduct field study, besides essential 
         clinical and pathology-trained staff; 

    (e)  Listing of toxicological studies to be carried out on
         laboratory animals.

3.3  Collection of Additional Pathological Samples

    Detailed autopsy/biopsy studies can be made on animals and 
patients.  A biopsy could be carried out as part of a diagnostic or 
therapeutic procedure, for example, carrying out a liver 
biopsy/kidney biopsy following paracentesis. 

3.4  Collection and Storage of Biological and Environmental Samples 
for Further Analysis 


    At the end of the entire process, after testing the validity of 
the hypothesis and after establishing the causal relationship 
between a chemical agent and the identified disease cases, the 
following steps are necessary: 

    (a)  Dissemination of knowledge concerning signs and symptoms 
         among health practitioners, in order to identify all cases 
         of the disease and to get an exact evaluation of the 
         magnitude of the outbreak/episode. 

    (b)  Search for even milder signs and symptoms among 
         subpopulations that have been exposed to the agent.  This 
         may result in the identification of borderline cases, 
         which will improve the accuracy of the evaluation.

    (c)  Identify the mechanism of the contamination and the 
         determinants of the exposure of specific subpopulations.

    (d)  Finally, identify the most relevant measures to either 
         remove the causal agent or minimize the exposure of the 
         population at risk. 



    Kashin-Beck disease was first described by Kashin and later by 
Beck & Beck in the Urov River area of eastern Siberia in the last 
century.  Further research and practical measures in the USSR 
resulted in the successful control of the endemic disease in this 

    In China, this disease, which has probably existed in the 
endemic regions for centuries, was first studied during the first 
half of this century.  However, it is only during the last decades 
that this health problem, prevalent in 14 out of 29 provinces, 
municipalities, and autonomous regions of mainland China, has 
received appropriate attention.  The basic pathological change in 
this disease, commencing mainly in children, is the degeneration 
and necrosis of articular cartilage and the growth plate, which can 
result in permanent disability.  Present estimates indicate that 
about 2 million people are affected by this disease and that more 
than 30 million people living in the endemic areas of China are at 
risk of acquiring it.  The disease seems to be linked with the 
consumption of food produced in the endemic areas and is possibly 
related to the presence of certain specific chemicals in food 
and/or water.  The People's Republic of China, expressing interest 
in the WHO/ILO/UNEP International Programme on Chemical Safety 
(IPCS), underlined the importance of this disease and, for this 
reason, a joint meeting was convened by the Ministry of Public 
Health of the People's Republic of China, the International 
Programme on Chemical Safety, and the Western Pacific Regional 
Office of the World Health Organization to review the status of 
present knowledge on this disease and its possible etiology. 

     Scope of the Meeting

    The meeting was held at the Institute of Health of the China 
National Centre for Preventive Medicine, in Beijing, from 
28 October to 1 November 1985.  After the opening by Professor 
Chen Chunming, Director the China National Centre for Preventive 
Medicine, the meeting was addressed by Dr Guo Ziheng, Vice-Minister 
of the Ministry of Public Health of the People's Republic of China, 
who explained the importance of the meeting for the promotion of 
studies on the chemical etiology of specific diseases.  The Vice-
Minister stressed the importance of the fact that the meeting on 
Kashin-Beck disease would be followed by a second IPCS meeting on 
criteria for establishing the chemical etiology of specific 
diseases as a basis for their prevention, which would be hosted by 
the same Institute, during the following week.  Dr E. Goon (WHO 
Representative, Beijing) and Dr J. Parizek (IPCS/WHO) addressed the 
meeting on behalf of WHO.  Professor Chen Chunming was elected 
Chairman, Professor V.A. Nasonova and Dr Niu Shiru, Vice-Chairmen, 
and Dr Chen Junshi and Dr O.A. Levander, Rapporteurs.  The 
background papers for the meeting are listed in Appendix I. 

    The papers on Kashin-Beck disease presented at the meeting by 
Chinese scientists reviewed: 

    (a)  the epidemiology, geographical distribution, and 
         clinical features;

    (b)  pathological and biochemical features; and

    (c)  prevention of the disease.

    In addition, a paper expressing the present views of a leading 
scientist from the region in the USSR where Kashin-Beck disease is 
endemic was presented, at the request of the organizers of the 
meeting from the People's Republic of China. 

    During the last day, related papers were presented on Keshan 
disease and of endemic human selenosis in China. 

     Summary of the results presented at the meeting: the current 
     situation concerning Kashin-Beck disease

1.  Main epidemiological characteristics

    (a)   Geographical distribution

    The disease mainly occurs in the mountainous and hilly areas of 
temperate forest and forest-steppe zones and is very rarely 
observed in the plains.  The climate in endemic areas usually 
includes a long period of frost and big differences between the 
daily minimum and maximum temperatures.  Affected villages are 
distributed in small foci within the endemic area.  The prevalence 
in neighbouring villages can vary significantly and can change with 
time.  New patients can be found in villages where patients have 
not been reported before.  In rare cases, the prevalence in 
certain, severely affected villages can decrease "spontaneously" so 
that, after about 10 years, no new cases occur. 

    (b)   Age of patients

    The disease mainly develops in 5- to 13-year-old children, and 
very few new cases are seen among adolescents and adults. In 
heavily affected areas, some new cases might be only 2 - 3 years of 
age, whereas, in lightly affected areas, some new cases may not 
occur until 10 years of age. 

    (c)   Family characteristics

    Within endemic areas, patients mainly occur in farming 
families.  Children of farm (government-owned) employees are also 
vulnerable).  Only very few cases occur in "professional" families.  
However, patients may occur in professional families, if they 
consume a large amount of the staple grains (corn, highland barley, 
wheat) produced in endemic areas.  The incidence of new and severe 
cases of the disease may decrease after changing the staple grains. 

    In contrast with other endemic diseases, such as Keshan 
disease, it is important to note that, in some sites where Kashin-
Beck disease is endemic, in recent years, the number of recognized 
cases is increasing.  The etiology of the disease remains obscure, 
but has been linked with certain chemical constituents of food and 
possibly water.  In China, Kashin-Beck disease mainly occurs in 
low-selenium areas, but selenium deficiency alone is not sufficient 
to explain the disease. The possible role of fungal  (Fusarium 
 oxysporum) or bacterial toxins was considered in some of the 
papers presented at the meeting. 

2.  Clinical signs and symptoms

    In the clinical development of the disease, weakness is 
followed by joint stiffness.  Limitation of flexion of the index, 
middle, and ring fingers towards the palm can be detected followed 
by limitation of elbow joint movement and joint enlargement and 
deformity.  Signs are similar to those of primary osteoarthrosis.  
In China, the disease has been clinically classified as follows: 

    -    Early stage: flexion of distal joint part of fingers,
         bow-like fingers, and pain in knee and ankle joints;

    -    First degree: enlargement and crepitus of small joints;

    -    Second degree: short fingers, enlargement and dysfunction 
         of medium-sized joints; 

    -    Third degree: enlargement and dysfunction of large joints 
         (stunted growth). 

"Muscular dystrophy" can be seen during the course of the disease. 

    X-ray examination reveals:

    (a)  the calcification line becoming blurred, thin, interrupted, 
         and disappearing as is characteristic for chondronecrosis; 

    (b)  defects of the metaphyseal plate, the end of distal bone, 
         and carpal and metacarpal bones following chondronecrosis;

    (c)  deformity of the epiphysis, synostosis of the epiphyseal 
         plate resulting from necrosis of the whole layer of the 
         epiphyseal plate; and 

    (d)  enlargement of joints and stubby fingers, the effects of 
         secondary osteoarthrosis. 

    Anatomical pathological examination reveals that lesions mainly 
involve hyaline cartilage.  The epiphyseal cartilage, articular 
cartilage, and epiphyseal growth plate are the most affected sites.  
Changes are "dystrophic" in nature.  The most important 
pathological feature is multiple localized chondronecrosis in the 
deep portion of cartilage tissue.  Chondronecrosis of the growth 

plate may result in disturbance of endochondral ossification and 
may even induce the early closure of the epiphyseal growth plate.  
The growth of long bones ceases and causes short fingers and toes, 
short limbs, and even stunted growth.  The chondronecrosis in 
articular cartilage may induce scar formation and result in bony 
enlargement, osteophyte formation, and disfiguration of the joints 
affected ("endemic osteoarthrosis deformans").  Disturbances of 
endochondral ossification of the growth plate and advanced 
secondary osteoarthrosis are the two cardinal manifestations of the 

    Biochemical research has indicated a series of metabolic 
disorders including: 

    (a)  changes in cartilage metabolism, mainly affecting 
         chondroitin sulfate and proteoglycan; 

    (b)  changes in clinical chemistry, including the plasma
         enzymes (e.g., alkaline phosphatase, glutamate-oxalo-
         acetate transaminase, beta-hydroxybutyrate dehydro-
         genase), and the urinary excretion of creatinine and 

    (c)  changes in the composition of certain lipids and selenium 
         in the red blood cell membranes; and 

    (d)  characteristics of low-selenium status, including changes 
         in glutathione peroxidase activity, tocopherol content, 
         and lipid peroxides in plasma. 

3.  Preventive measures

    The following techniques for the prevention of Kashin-Beck 
disease have been studied by Chinese scientists and were discussed 
at the meeting.  All these approaches have been used in studies on 
subpopulations of varying sizes, and positive results from 
individual studies were reported at the meeting. 

    (a)   Comprehensive prevention

    Encourage the children to diversify their foods (variety and 
source), offer two servings/week of soup containing soybeans, sea 
weed, and multiple vitamins.  Purify drinking-water (use deep well 
water with precipitation) and improve personal hygiene.  It has 
been reported that, with this scheme, the prevalence of X-ray 
changes and of changes in the metaphysis decreased. 

    (b)   Selenium intervention

    Three different measures have been used for selenium 
supplementation including: 

    (i)   oral administration of sodium selenite at 1 mg/week
          or 2 mg/week to children of 7 - 10 years and 11 - 13
          years, respectively;

    (ii)  selenized table salt containing a sodium selenite
          concentration of 16.7 mg/kg; and

    (iii) spraying sodium selenite solution on wheat crops at
          the rate of 15 g/ha (1 g/mu)a.

Using these measures, incidence rates dropped within one year, and 
recovery from changes in the metaphysis was noted. 

    (c)   Water quality

    Water can be purified by precipitation, filtration, and 
chlorination.  This technique and/or the use of deep groundwater 
have both been associated with an improvement in clinical symptoms 
and a reduction in incidence rate. 

    (d)   Change of grains

    Changing the locally produced grain for grains produced in 
other areas led to the prevention of new cases, a decreased 
incidence of X-ray changes, and better recovery from meta-physeal 

    In endemic areas of the USSR, significant reductions in the 
prevalence rates and the severity of Kashin-Beck disease were 
connected with special governmental and public health measures.  
The most effective measures were the organization of population 
migration from endemic to non-endemic regions, the importation of 
food from non-endemic areas, thermal treatment of local products 
and water, annual check-ups on children and adult populations in 
endemic regions by public health personnel, and the development of 
appropriate health education programmes.  On the basis of the 
theory of biogeochemical provinces linking certain endemic diseases 
with the geochemical characteristics and quality of the soil and 
water in certain areas, studies in the USSR related very high 
phosphate and manganese contents in the soil, food, and drinking-
water in the endemic area with Kashin-Beck disease. Reducing the 
contents of these chemicals in food and water is part of the 
present preventive measures in the USSR.  As mentioned in the 
discussion, differences in selenium levels were not detected 
between the affected and non-affected areas studied in the USSR. 

4.  Conclusions and recommendations

    (a)  Kashin-Beck disease is a highly disabling disease of 
    permanent character that mainly affects children.  In China
    alone, about 2 million people are affected, at present, and
    more than 30 million people living in the endemic areas are at 
    direct risk of acquiring the disease.  All the evidence 
    indicates that the disease is caused by a certain quality of 
    the environment, specific for the endemic regions, which 

a 1 mu = 0.0667 ha. From: Beijing Language Institute (1979)
   Chinese English Dictionary, Beijing, Commercial Press.

    encompass a large part of China and parts of neighbouring 
    countries.  Several studies indicate the involvement of certain 
    chemicals in food and water (manganese, phosphorus, mycotoxins, 
    microbial toxins, humic acid, etc.), as well as nutritional 
    imbalance, in particular, selenium deficiency, as factors 
    contributing to the etiology of this disease.

    A coordinated effort is needed to elucidate the etiology of 
    this disease, which is endemic in a very specific area of Asia.  
    Cooperation among countries affected by the disease should be 
    supported by international organizations with the aim of 
    developing uniform diagnostic criteria and protocols for 
    epidemiological studies to test the above hypotheses and 
    elucidate more precisely the cause of the disease and 
    contributing factors.  Exchange of information on effective 
    measures for the prevention of the disease should be another 
    component of such intercountry cooperation, as well as the 
    training of personnel needed for preventive, diagnostic, and 
    therapeutic activities.  As a first step in this direction, 
    exchange of scientists between the countries with endemic 
    regions should be supported as well as the development of 
    methods and their use in the above-mentioned cooperative 

    Such activities would significantly contribute towards 
    chemical safety and the solution of a problem affecting 
    populations in several neighbouring member states.

    (b)  Kashin-Beck disease primarily affects the joints.
    However, the relation with other osteoarthroses is not clear, 
    and the possible etiological factors involved are not known.

    Thus, in cooperation with non-governmental and other
    organizations, a meeting should be convened to define specific 
    characteristics, identify risk factors, and consider 
    possibilities for the prevention and control of this disease 
    and its possible relationship with other osteoarthroses.

    (c)  In spite of the public health significance of Kashin-Beck 
    disease, the disease does not seem to be sufficiently 
    recognized in the medical literature.  In this respect, the 
    data presented at this meeting was considered highly 

    It was recommended that the co-sponsoring organizations should 
    explore the possibility of publishing the full proceedings of 
    this meeting as a monograph.  The possibility of making the 
    video tape that was prepared in the endemic regions for the 
    meeting more widely available should also be explored.



Professor L. Amin-Zaki, Consultant Paediatrician, Central Hospital, 
   Abu Dhabi, United Arab Emirates

Professor E.A. Bababunmi, Director, Laboratory of Biomembrane
   Research, Department of Biochemistry, University of Ibadan, 
   College of Medicine, Ibadan, Nigeria

Dr R.V. Bhat, National Institute of Nutrition, Indian Council of 
   Medical Research, Hyderabad, India

Dr J. Borgoño, Professor of Preventive Medicine, University of
   Chile, Chief, Department of International Affairs, Ministry of 
   Health, Santiago, Chile

Dr Y. Egashira, Honorary Staff, National Institute of Health, 
   Hatano Research Institute, Food and Drug Research Centre, 
   Hatanoshi, Kanagawa-ken, Japan

Dr R.A. Goyer, Deputy Director, National Institute of Environmental 
   Health Sciences, Research Triangle Park, North Carolina, USA

Dr P. Grandjean, Institute of Community Health, Department of
   Environmental Medicine, Odense University, Odense, Denmark

Dr V.N. Ivanov, Director, Chita Medical Institute, Chita, USSR

Dr V.V. Ivanov, Chief, Department of Pathophysiology, Krasnoyarsk 
   Medical Institute, Krasnoyarsk, USSR

Dr R.D. Kimbrough, Research Medical Officer, Toxicology Branch,
   Clinical Chemistry Division, Bureau of Laboratories, Center for 
   Environmental Health, Centers for Disease Control, Atlanta, 
   Georgia, USA 

Professor P. Krogh, Department of Microbiology, Royal Dental
   College, Copenhagen, Denmark

Dr O.A. Levander, Vitamin and Mineral Nutrition Laboratory,
   Nutrition Institute, US Department of Agriculture, Beltsville, 
   Maryland, USA  (Co-Rapporteur) 

Dr K.R. Mahaffey, Division of Standards Development and Technology 
   Transfer, National Institute for Occupational Safety and Health, 
   Cincinnati, Ohio, USA 

Dr G. Martin-Bouyer, Conseiller Technique, Ministère des Affaires 
   Sociales et de la Solidarité Nationale, Direction Générale de la 
   Santé, Paris, France 

Professor V.A. Nasonova, Director, Institute of Rheumatology,
   Academy of Medical Sciences of the USSR, Moscow, USSR

Professor H.D. Tandon, formerly Director, All India Institute of 
   Medical Sciences, New Delhi, India 

Professor H. Yanagawa, Department of Public Health, Jichi Medical 
   School, Minamikawachi, Tochigi-ken, Japan 

Dr Bai Shicheng, The Basic Medical Institute of Liaoning Province, 
   Shenyang, People's Republic of China 

Professor Chen Chunming, Director, China National Center for
   Preventive Medicine (CNCPM), Beijing, People's Republic of
   China  (Chairman)

Dr Chen Junshi, Deputy Director, Department of Nutrition and Food 
   Hygiene, Institute of Health, China National Centre for 
   Preventive Medicine, Beijing, People's Republic of China 

Dr Chen Xiaoshu, Deputy Director, Institute of Health, China
   National Centre for Preventive Medicine, Beijing, People's
   Republic of China

Dr Deng Jiayun, The Health and Antiepidemic Station of Sichuan
   Province, Chengdu, People's Republic of China

Dr Geng Jinzhong, Deputy Director, Division of Environmental
   Hygiene, Ministry of Public Health, Beijing, People's Republic 
   of China 

Dr Guo Xiong, Research Laboratory of Endemic Bone Disease, Xian 
   Medical University, Xian, People's Republic of China 

Professor Li Fangsheng, The Basic Medical Institute of Liaoning 
   Province, Shenyang, People's Republic of China 

Dr Li Guangshen, Institute of Endemic Disease, Norman Bethune
   University of Medical Sciences, Changchun, Jilin Province,
   People's Republic of China

Professor Li Jiyun, Northwestern Institute of Soil and Water
   Conservation, Chinese Academy of Sciences, Shaanxi, People's 
   Republic of China 

Dr Li Sheng, Deputy Director, Division of Technical Assistance
   and Development, China National Center for Preventive Medicine, 
   Beijing, People's Republic of China 

Dr Li Chongzheng, Institute of Prevention and Cure of Endemic
   Diseases, Gansu Province, People's Republic of China

Dr Liang Shutang, Institute of Prevention and Cure of Endemic
   Diseases, Shaanxi Province, People's Republic of China

Dr Ma Tai, Tianjin Medical College, Tianjin, People's Republic of 

Dr Mo Dongxu, Research Laboratory of Endemic Bone Diseases, Xian 
   Medical University, Xian, People's Republic of China 

Dr Niu Guanghou, The Health and Antiepidemic Station of 
   Heilongjiang Province, Haerbin, People's Republic of China 

Professor Niu Shiru, Director, Institute of Health, China
   National Centre for Preventive Medicine, Beijing, People's
   Republic of China  (Vice-Chairman)

Professor Peng An, Institute of Environmental Chemistry, Chinese 
   Academy of Sciences, Beijing, People's Republic of China

Professor Ren Hongzao, The Basic Medical Institute of Liaoning
   Province, Shenyang, People's Republic of China

Dr S. Shibata, Director, Division of Clinical Research, National 
   Medical Centre of Japan 

Dr Sun Xi, Head, Division of Science and Technology, Office for
   Endemic Diseases (CPCCC), Shenyang, People's Republic of China

Professor Tan Jianan, Institute of Geography, Chinese Academy of 
   Sciences, Beijing, People's Republic of China 

Dr Xi Guangzeng, The 323 Hospital of the People's Liberation Army, 
   Xian, People's Republic of China 

Dr Xu Guanglu, Research Laboratory of Keshan Disease, Xian Medical 
   University, Xian, People's Republic of China 

Professor Yang Fuyu, Institute of Biophysics, Chinese Academy of 
   Sciences, Beijing, People's Republic of China 

Professor Yang Guangqi, Department of Nutrition and Food Hygiene, 
   Institute of Health, China National Centre for Preventive 
   Medicine, Beijing, People's Republic of China 

Professor Yang Jianbo, Haerbin Medical University, Haerbin, 
   People's Republic of China 

Professor Yang Tongshu, Institute of Endemic Disease, Normal
   Bethune University of Medical Sciences, Changchun, People's 
   Republic of China 

Dr Yin Peipu, Institute of Endemic Bone Diseases, Xian Medical
   University, Xian, People's Republic of China

Dr Ying Mingxin, Haerbin Medical University, Haerbin, People's
   Republic of China

Professor Yu Weihan, Haerbin Medical University, Haerbin, People's 
   Republic of China 

Dr Zhai Shusheng, The Second Institute of Prevention and Cure of 
   Endemic Diseases, Jilin Province, People's Republic of China

Dr Zhao Tieli, Deputy Director, Office for Prevention of Endemic 
   Diseases (CPCCC), Shenyang, People's Republic of China

Dr Zhou Zhenglong, Institute of Prevention and Cure of Endemic
   Diseases, Shanxi Province, People's Republic of China

 Representatives from Other Organizations

Dr R. Hoffmann, Senior Programme Officer, United Nations Children's 
   Fund (UNICEF), Beijing, People's Republic of Chinaa

Dr Zhang Naizheng, International League Against Rheumatism (ILAR), 
   Capital Hospital, Chinese Academy of Medical Sciences, Beijing, 
   People's Republic of China 


Dr Eric H.T. Goon, WHO Representative and Programme Coordinator, 
   Beijing, People's Republic of China 

Dr M. Mercier, International Programme on Chemical Safety, World 
   Health Organization, Geneva, Switzerland 

Dr M. Mitrofanov, Division of Noncommunicable Diseases, World
   Health Organization, Geneva, Switzerland

Dr J. Parizek, International Programme on Chemical Safety, World 
   Health Organization, Geneva, Switzerland  (Secretary) 

Dr Xu Genlin, Director, Office of Research Management, Institute of 
   Health, Beijing, People's Republic of China 

Dr Yao Peipei, Division of Pneumoconiosis, Institute of Health,
   Beijing, People's Republic of China

Dr Liu Yuying, Division of Industrial Toxicology, Institute of
   Health, Beijing, People's Republic of China

Dr Wang Zhiwu, Institute of Kashin-Beck Disease of Heilong-jiang 
   Province, Haerbin, People's Republic of China 

a Attended the opening of the meeting.

    See Also:
       Toxicological Abbreviations