[History of insular malaria in the southwestern Indian Ocean: an eco-epidemiologic approach]

Abstract

Madagascar has been isolated from the African continent since the Mesozoic era. The archipelago in this region emerged from volcanism during the early and the beginning of the late Cenozoic era. Consequently, during the prehistoric period, these islands were populated by only birds. Parasites and their vectors have been imported. In Madagascar (with the exception of the highlands) and in certain Comoro Islands, their implantation in a favorable biotope was contemporary with the coming of humans. The late introduction of malaria in the "Grand" Comoro island was the result of major human modification of the environment (construction of rainwater tanks), which was associated with the adaptation of the vector. In these zones, malaria is a stable type, with permanent transmission and seasonal reinforcement. From Madagascar, the vector was possibly introduced to Mauritius via a steamship line. This hypothesis is consistent with the biological constraints of the anopheles vector in that the inter-island distance was shortened. Also, transport of the vector by wind during a cyclone from Mauritius to Réunion cannot be excluded. Once introduced, the vectors were in an environment sufficiently reshaped by humans (deforestation) to allow implantation of a heliophile species like A. gambiae s.l. In Mauritius, after repeated eradication campaigns by spraying within the homes, anopheles emerged without transmission of malaria. The islands of Rodriguez and the Seychelles, protected by their geographical isolation, remain unscathed due to the absence of the vector.