Premunition against Plasmodium falciparum in a malaria hyperendemic village in Myanmar

Abstract Premunition, naturally acquired protective immunity against Plasmodium falciparum , has been described in hyperendemic areas of Africa and Papua New Guinea. However, its occurrence in Asia is debatable. In order to elucidate this question, a longitudinal study was undertaken in Oo-Do, a malaria endemic village in Myanmar [Burma] in 1995–1997. Only 2 species, Plasmodium falciparum 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 period of 3 years, with a 38% reinfection rate after eradication of patent parasitaemia. The high rate of prevalence (90–100%) of parasite-specific antibodies in the indirect immunofluorescence antibody test and the presence of 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, malarial episodes occurred more frequently in children than in adults ( P = 0 · 001). Taken together, all these facts indicated that the inhabitants of Oo-Do had progressively developed non-sterile partial protective immunity against P. falciparum malaria, or premunition. To our knowledge, this is the first detailed clinico-epidemiological study to document the occurrence of premunition in Myanmar.