The schistosomiasis problem in the world: results of a WHO questionnaire survey.

This article presents an overview of the magnitude of the schistosomiasis problem throughout the world, and is based on information on schistosomiasis control programmes provided by 103 countries in reply to a questionnaire circulated by the World Health Organization in 1976. According to the data either given in these replies, published, or provided in internal reports to WHO, schistosomiasis is one of the most widespread parasitic infections of man. Some 500 million people are thought to be exposed to infection and four main species of schistosomes are prevalent, together with their various intermediate snail hosts, in 73 countries. Control programmes are operating in 41% of responding endemic countries although they are on a national scale only in Brazil, Dominican Republic, Egypt, Iran, Iraq, Japan, Morocco, Puerto Rico, St Lucia, Tunisia, and Venezuela. It appears that a maximum of only 1-2% of all cases have been treated, the most frequently used drugs being niridazole and hycanthone. A small number of efficient molluscicides are in regular use but their high cost precludes large-scale application. Installation of water supplies and health education are the most frequently used non-specific control measures. Nearly 50% of endemic countries use more than three different methods of control simultaneously. The national schistosomiasis control programmes in Brazil, Egypt, Iran, Japan, Puerto Rico, and Venezuela are examples of combined approaches that have resulted in a significant decline in the prevalence of schistosomiasis. Finally, some specific needs in research, control, and training of personnel are discussed.