S mansoni S intercalatum

Figure 2 The geographical distribution of schistosomiasis (from WHO).

Safe, effective chemotherapy against all the schisto-somes that infect humans has been available for more than two decades (WHO, 1993). The most versatile drug currently available is praziquantel, which is effective in a single oral dose, although it is relatively expensive if used extensively (approximately US $0.35 per treatment). However, treatment can result in resolution of infection, prevention or arrest of disease in heavily infected people and reversal of some manifestations of infection, such as haematuria.

Avoidance of contaminated water would prevent infection with schistosomes and is a relatively simple thing for occasional visitors to endemic areas to achieve. Control and prevention of infection in the community, however, where residents do not always have the luxury of avoiding contact with contaminated water, are complex. Many countries have initiated control programs involving a many pronged approach, including (1) the use of chemotherapy to remove adult worms, (2) elimination of the snail intermediate hosts by habitat modification or chemical attack, (3) changing human behaviour through health education and (4) providing safe water supplies and sanitation.

Use of these integrated control measures over many decades has led to the recent eradication of schistosomiasis in Japan, Tunisia and Monserrat (WHO, 1993). In China, 40 years of unremitting control measures have reduced the prevalence of infection by about 90%. Elsewhere in the World, including Brazil, Egypt, Iran, the Philippines and Venezuela, significant reductions in disease prevalence have been achieved. Even in places where the prevalence of infection has remained high, serious manifestations of disease are becoming less common with the use of effective chemotherapy, although declines in cancer incidence are not yet apparent (WHO, 1993). Despite this, the number of cases of schistosomiasis worldwide was estimated to be the same in 1993 as it was in 1984 (WHO, 1993). In endemic areas, populations (and hence the number of susceptible hosts) continue to grow. In addition, developments in water resource management, land use and irrigation have led to a spread of schistosomiasis to new areas. There is currently no vaccine available, although intensive efforts are being made to develop one, and so the use of complex, integrated control measures remains paramount.

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