Atopy and malaria.

The last decades have seen a dramatic rise in the prevalence of allergic diseases throughout the industrialised world. The "hygiene hypothesis" postulates that this is due to a reduced exposure to infections during childhood. A cohort study in children from Gabon gave us the unique opportunity to examine the relationship between exposure to P. falciparum and atopy. 91 children, who had been closely followed for an average of 5 years and of whom the exact incidence of malaria attacks was known, underwent a skin-prick test with mite antigen. 16 children (18%) had a positive reaction. Gender or age had no effect on the outcome of the test. However, those tested positive had had less infections and a lower incidence of malaria than children tested negative (p = 0.017). Survival analysis shows that children with a high exposure to P. falciparum were at lower risk of an atopic skin reaction (p = 0.001). We postulate that the low exposure to the malaria parasite contributes to the development of an imbalanced immune system with a subsequent higher reactivity to the allergen tested. Immuno-suppression is commonly seen during a malaria attack and this correlates positively with the level of anti-inflammatory cytokines such as interleukin-10. High exposure to parasite antigens might counterbalance pro-inflammatory immune reactions and thus protect against allergic diseases. A better understanding of the relationship between parasitic infection and allergy will help us to develop strategies to prevent allergic disease without being exposed to infectious diseases.