Exposure, infection and immune responses to Schistosoma haematobium in young children

Behavioural, parasitological and immunological data were obtained from 48 c hildren up to 6 years old, resident in a Schistosoma haematobium endemic ar ea in Zimbabwe. The children averaged more than 1 contact with infective wa ter bodies every 3 days and all showed immunological evidence of exposure ( an anti-cercarial and/or anti-egg antibody response). IgM was the dominant isotype and appeared in the youngest children, followed by IgA, IgE and IgG 3. However, only 38 children showed evidence of infection (an anti-egg resp onse or eggs in urine) and only 14 were excreting eggs. The best estimates from these data are that less than 1 in 100 contacts result in infection an d less than 1 in 1000 result in egg output. This suggests that there may be substantial attrition of invading cercaria even in naive individuals.