Atopy Is Inversely Related to Schistosome Infection Intensity: A Comparative Study in Zimbabwean Villages with Distinct Levels of Schistosoma haematobium Infection

BACKGROUND: The hygiene hypothesis suggests that parasitic infections protect against allergic diseases by modulating the host's immune responses. Experimental studies indicate that this protection depends on the intensity of parasitic infection, but this observation has not been tested in human populations. The aim of this study is to investigate whether the intensity of Schistosoma haematobium infection is related to atopic responses and whether this relationship differs between populations with distinct parasite transmission dynamics. METHODS: The study was conducted in two villages with different Schistosoma haematobium transmission dynamics, i.e. high (n = 365) and low (n = 307) transmission. Allergic reactivity to the common house dust mite (Dermatophagoides pteronyssinus) was measured by skin prick tests and allergen-specific IgE and IgG4 quantified by enzyme-linked immunosorbent assay. Atopic responses were related to current infection intensity and schistosome transmission levels. RESULTS: Schistosome infection intensity was negatively associated with the skin prick reactivity, mite-specific IgE and the ratio IgE/IgG4 in the high-transmission village. However, when only low levels of infection were analyzed in the 2 villages, there was no correlation between mite-specific responses and infection intensity. CONCLUSION: The relationship between schistosome infection and atopic responses is dependent on the intensity of current schistosome infection. Thus, consistent with results from animal models, with an increasing parasite burden, the immunoregulation of immune responses to allergens appears to become more pronounced.