The effects of schistosomiasis on the behaviour of children.
An ethological study was undertaken in two primary schools in Natal to assess the effect of schistosome infections on the ordinary behaviour of schoolchildren in endemic areas. The following topics are discussed :- 1. The life cycle of the parasite, the possibility of an evolved tolerance of it, the likely limits of such tolerance, the possibility of selective exposure of certain kinds of children to the parasite, and the role of severity of infection in impairment. 2. Appropriate measures for investigating the impairment of the human host centring around the measurement of activity in the context of social interaction. 3. An ethological approach to evaluating human response to disease. Results indicate that there is selective exposure of more active, sociable children to the disease. In low-level infections of both Schistosoma haematobium and Schistosoma mansoni there is little evidence of a drop in energetic activity under normal conditions. In subjects with higher egg counts or simultaneous infections with both schistosomes, activity levels drop generally, and especially under hot, humid weather conditions where the drop in activity is greater than that for control subjects. This work throws doubt on earlier studies indicating that the parasite had no behavioural effect on humans: these studies did not control for selective exposure and may have used methods of low sensitivity and doubtful relevance to everyday life.