AGGREGATION IN SCHISTOSOMIASIS - COMPARISON OF THE RELATIONSHIPS BETWEEN PREVALENCE AND INTENSITY IN DIFFERENT ENDEMIC AREAS

Distributions of the intensities of helminth infections within their h ost populations are invariably aggregated. In the case of the intestin al nematodes, the degrees of aggregation have been shown to be species specific, and constant for any given species despite geographical var iation in study sites. This species-specific aggregation can be quanti fied and used as a tool in planning control interventions. One practic al application is that the prevalence of infection can be used to pred ict the prevalence of heavy infection and thus the risks of morbidity. This paper investigates the patterns of aggregation in schistosome eg g counts in different endemic areas in Africa (data sets were obtained from Burundi, Cameroon, Tanzania, Zambia and Zaire). The analysis dem onstrates that the degree of parasite aggregation, for both Schistosom a mansoni and S. haematobium, differs amongst the different study loca lities. This is probably due to area-specific differences in host expo sure and immunity. This implies that for these schistosome species, it is not possible to predict egg count distributions or morbidity level s from prevalence data alone.