Intestinal helminth infections are associated with increased incidence of Plasmodium falciparum malaria in Thailand

Abstract

In a prospective study of the total population of 5 hamlets on the western border of Thailand, all subjects were screened for helminth infections; during the following year, the incidence of malaria was recorded. Patients were not treated for helminth infections. Among 731 villagers, helminth-infected subjects were more likely to develop falciparum malaria during the following year (adjusted risk ratio 2.24, range 1.4-3.6; P = 0.001). The risk of developing falciparum malaria increased with the number of helminth species (P =0.036). Whereas in other studies helminths were associated with protection from severe complications of malaria, it seemed here that helminth infected patients were more likely to develop malaria. It is suggested that a helminth-mediated Th2 shift may have complex consequences on malaria, decreasing antisporozoite immunity, but protecting against severe malaria.