The epidemiology of Schistosoma haematobium and S. mansoni infections in the Egypt-49 project area. 3. Prevalence of bilharziasis in relation to certain environmental factors.

The influence of the size and location of communities in relation to the different types of watercourse, the availability of a protected water supply, types of housing and the presence of other sanitary facilities on the prevalence of bilharziasis in the Egypt-49 project area has been studied. There is no direct relationship between the size of village and the prevalence of bilharziasis. Main drains and distributaries are potent sources of infection and, in terms of the total population exposed, distributaries play the most significant role in the transmission of infection. Of the other factors, the availability of a protected water supply seems to have the greatest effect on the prevalence. Although the presence of a latrine in the dwelling does not of itself influence the extent of schistosome infection, which is caught from polluted water, the installation of latrines assists in the cultivation of healthy habits, thereby lessening the prevalence not only of bilharziasis but also of certain other infections.