ENVIRONMENTAL DISEASE 



dustry, social structure, social change, 

 and economic development. The dis- 

 ease affects mainly the poorer people 

 closest to the soil. Low economic 

 status promotes the disease because it 

 forces people to live in unsanitary 

 conditions. Ignorance is also a major 

 factor in lack of sanitation. The dis- 

 ease causes significant illness and de- 

 bility in a large proportion of the 

 infected population. These people 

 compete less well and are less produc- 

 tive. The disease, then, holds them 

 down. Farmers, because of the nature 

 of their work, are more often exposed 

 to the infection. Urbanization reduces 

 the danger of spread of the disease, 

 but water resources development 

 schemes — with their dams, irrigation 

 systems, and water-level-stabilization 

 activities — promote the transmission 

 of the disease. Water resources devel- 

 opment schemes that can produce 

 significant economic and social ad- 

 vancement can be severely weakened 

 by the spread of this disease that can 

 result directly from the changes the 

 schemes require. 



Current Scientific Knowledge — We 

 know enough to control schistosomi- 

 asis in most of the endemic zones. 

 The way to do it is by reducing snail 

 populations and contact of man with 

 "infected" water. New molluscicides 

 offer a reasonably economical oppor- 

 tunity to reduce transmission drastic- 

 ally. New drugs are in development 

 that offer for the first time a hope for 

 easy treatment with reduced toxicity. 

 There is no reasonable prospect of a 

 vaccine or other means for control 

 of the disease except, perhaps, for 

 use of competitor snails in some 

 localities. 



Needed Activity — The technical 

 base is thus reasonably good. Of 

 course, more information would help. 

 Safer drugs, easier snail control, and 

 a way to vaccinate against the disease 

 can be hoped for. Recently, there has 

 been a series of efforts to produce 

 mathematical models for analysis of 

 transmission problems and for predic- 

 tion. They are in the exploratory 



phase and are not really predictive yet. 

 Figure X-21 is one input to such a 

 model. 



But control schemes will need more 

 trained people, support, and — per- 

 haps hardest to get — good national 

 organizations devoted to the problem. 

 We have spent enough time "finding 

 out" what we need to know about the 

 problem. We need to get on with con- 

 trol schemes and continue to learn 

 as we go along. A strong push could 

 work wonders in control of the dis- 

 ease in a number of countries. 



Chagas' Disease 

 (American Trypanosomiasis) 



Chagas' disease occurs in almost all 

 American countries and exists in re- 

 gions inhabited by about 35 to 40 

 million people. At least 7 million are 

 usually considered to be infected, 

 though the number is sometimes esti- 

 mated to be as high as 10 million. In 

 some endemic zones, 50 percent or 

 more of the people are infected; of 

 these, 10 to 20 percent have signifi- 

 cant cardiac damage or intestinal-tract 

 damage due to the infection. Morbid- 

 ity and mortality data are not very 

 good. One careful study of the causes 

 of death that occurred in Ribeirao 

 Preto, Brazil, over a two-year period 

 showed that the disease was the cause 

 of 29 percent (40 out of 139) of the 

 male mortality in the 25 to 44 year 

 age group — a shocking figure. Ar- 

 gentina considers that it has 2 million 

 infected citizens and 400,000 with 

 heart damage or other significant con- 

 sequences of the infection. Venezuela 

 has about 2.8 million people exposed 

 to the infection in the endemic zones 

 and about 560,000 infected persons, 

 of whom about half have significant 

 cardiac damage as a result. 



Chagas' disease is a disease of the 

 poor, ignorant, and badly housed. It 

 is primarily rural, though some cities 

 are heavily affected in the poorer 



parts. Poverty and lacl 

 tion results in constrm bad 



houses of poor materials and in poor 

 maintenance of houses. Such houses 

 are excellent harborages for the insect 

 vectors. The disease produces, in a 

 proportion of its victims, acute illness 

 followed by delayed cardiac or diges- 

 tive-tract damage. These can termi- 

 nate in heart failure, invalidism, and 

 loss of productivity. The disease 

 strikes particularly hard among young 

 adults in their most productive years 

 and when their families are most 

 vulnerable to economic stress. The 

 circle of poverty-ignorance-sickness- 

 economic failure is a difficult one to 

 break. 



Venezuela is the only country with 

 a control program of a size and sig- 

 nificance commensurate with the size 

 of the problem. A few other countries 

 have limited control programs (partic- 

 ularly Chile, Brazil, and Argentina). 

 Many countries do not know the mag- 

 nitude of their problem with any ac- 

 curacy at all though in many of them 

 there is undoubted widespread mor- 

 bidity due to the disease. 



Current Scientific Knowledge — 

 Knowledge of the disease is now ade- 

 quate for effective control. What is 

 needed is the decision that control is 

 worth the cost and that it must be 

 undertaken. Systematic use of insec- 

 ticide (benzene hexachloride or diel- 

 drin) can cut the transmission rate 

 to a low level. Spraying costs $5 to 

 $10 per house and may have to be 

 repeated every two to three years. 

 This is relatively costly, considering 

 the political and economic status of 

 the people affected and considering 

 the inability of most of the countries 

 to spend large sums on disease control. 



In a number of countries, it is nec- 

 essary to determine the importance of 

 the problem. This can be done by 

 systematic sampling to determine 

 prevalence of infection (serological 

 test) and prevalence of significant 

 morbidity (electrocardiogram). Both 

 are technically feasible in any country. 



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