Schistosoma haematobium in a Gambian community. I. The intensity and prevalence of infection.

The intensity and prevalence of Schistosoma haematobium infection has been measured in a community in the laterite plateau area of the McCarthy Island Division, The Gambia. The prevalence reaches 100% by the age of 10 years and counts of over 1000 ova in 10 ml of noon urine are common. During the second and third decade prevalence and intensity of infection decline and the mean egg output of a cohort falls by approximately 50% every three years. In subjects aged over 30 sex differences in exposure to infection and egg output suggest the possible effect of protective immunity.