HIGH-INCIDENCE OF MALARIA IN ALPHA-THALASSEMIC CHILDREN

THE alpha(+)-thalassaemias are the commonest known human genetic disor ders, affecting up to 80 per cent of some populations(1). Although the re is good evidence from both epidemiological(2,3) and clinical(4) stu dies that these gene frequencies reflect selection by, and protection from, malaria, the mechanism is unknown. We have studied the epidemiol ogy of malaria in childhood on the southwestern Pacific island of Espi ritu Santo in Vanuatu and here we report that, paradoxically, both the incidence of uncomplicated malaria and the prevalence of splenomegaly , an index of malaria infection, are significantly higher in young chi ldren with alpha(+)-thalassnemia than in normal children. Furthermore, this effect is most marked in the youngest children and for the nonle thal parasite Plasmodium vivax. The alpha(+)-thalassaemias may have be en selected for their ability beneficially to increase susceptibility to P. vivax, which, by acting as a natural vaccine in this community, induces limited cross-species protection against subsequent severe P. falciparum malaria.