Premunition against Plasmodium falciparum in a malaria hyperendemic village in Myanmar

Premunition, naturally acquired protective immunity against Plasmodium falc iparum, has been described in hyperendemic areas of Africa and Papua New Gu inea. However, its occurrence in Asia is debatable. In order to elucidate t his question, a longitudinal study was undertaken in Go-Do, a malaria endem ic village in Myanmar [Burma] in 1995-97. Only 2 species, Plasmodium falcip arum and P. vivax, were detected, with the former predominating. Data from 116 subjects showed that all were infected at one time or another, over a p eriod of 3 years, with a 38% reinfection rate after eradication of patent p arasitaemia. The high rate of prevalence (90-100%) of parasite-specific ant ibodies in the indirect immunofluorescence antibody test and the presence o f the primary vector (Anopheles minimus) and 15 other species of Anopheles throughout the year indicated a high level of transmission. The spleen rate was 70% in 5-9 years old children and was inversely related with age. The incidence of parasitaemia was maximal (49%) in children aged 2-4 years, and then declined marginally with age. There was a significant difference (P = 0.001) between the asymptomatic and febrile parasitaemia levels. Also, mal arial episodes occurred more frequently in children than in adults (P = 0.0 01). Taken together, all these facts indicated that the inhabitants of Go-D o had progressively developed non-sterile partial protective immunity again st P. falciparum malaria, or premunition. To our knowledge, this is the fir st detailed clinico-epidemiological study to document the occurrence of pre munition in Myanmar.