Surveys were made of the prevalence of schistosomiasis in 16 irrigation farms in the Awash Valley, some nearby villages of indigenous pastoralists and subsistence farmers, and 21 towns and villages in the main labor source areas in the Ethiopian highlands. The results indicate that schistosomiasis mansoni is endemic only in the upper part of the Awash Valley, that it is absent from most home areas of the migrant farm laborers but highly prevalent in some localities, and that schistosomiasis haematobium is endemic only in the swamps and some lakes in the middle and lower parts of this valley. Schistosoma mansoni infection rates ranged from 0.8% to 15.2% among migrant farm populations, from 0% to 33.9% among indigenous pastoralists and farmers, and from 0% to 72.0% among school children in the main labor source areas. S. haematobium infection rates were lower than 2% in all migrant farm populations except one (20.0%) located in swamps where the parasite is endemic. Among indigenous pastoralists, rates varied between 0% and 26.9% in different parts of the valley. Snails were collected from the habitats visited and were identified, and susceptibility of Bulinus (Bulinus) truncatus/sericinus to S. haematobium was studied. The role of Bulinus (Physopsis) abyssinicus in the transmission of S. haematobium, as well as the influence of some environmental factors on the distribution of Biomphalaria pfeifferi and of labor migrations on schistosomiasis occurrence are discussed.
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