Exposure, infection, systemic cytokine levels and antibody responses in young children concurrently exposed to schistosomiasis and malaria

Despite the overlapping distribution of Schistosoma haematobium and Plasmodium falciparum infections, few studies have investigated early immune responses to both parasites in young children resident in areas co-endemic for the parasites. This study measures infection levels of both parasites and relates them to exposure and immune responses in young children. Levels of IgM, IgE, IgG4 directed against schistosome cercariae, egg and adult worm and IgM, IgG directed against P. falciparum schizonts and the merozoite surface proteins 1 and 2 together with the cytokines IFN-γ, IL-4, IL-5, IL-10 and TNF-α were measured by ELISA in 95 Zimbabwean children aged 1-5 years. Schistosome infection prevalence was 14·7% and that of Plasmodium infection was 0% in the children. 43. 4% of the children showed immunological evidence of exposure to schistosome parasites and 13% showed immunological evidence of exposure to Plasmodium parasites. Schistosome-specific responses, indicative of exposure to parasite antigens, were positively associated with cercariae-specific IgE responses, while Plasmodium-specific responses, indicative of exposure to parasite antigens, were negatively associated with responses associated with protective immunity against Plasmodium. There was no significant association between schistosome-specific and Plasmodium-specific responses. Systemic cytokine levels rose with age as well as with schistosome infection and exposure. Overall the results show that (1) significantly more children are exposed to schistosome and Plasmodium infection than those currently infected and; (2) the development of protective acquired immunity commences in early childhood, although its effects on infection levels and pathology may take many years to become apparent.