[Epidemiological stratification of malaria in Madagascar]

Madagascar is considered as a sub-region of the Afrotropical geographical Region in spite of the high endemicity of 95% of the invertebrates. Nevertheless the three malaria vectors An. gambiae s.s., An. arabiensis and An. funestus are quite similar to those of the continental Africa. This support the hypothesis of their recent introduction. Plasmodium falciparum is the dominant parasite but the prevalence of P. vivax is not negligible. It is linked to the Asian component of the human population. P. malariae and P. ovale are of minor importance. The main epidemiological "facies" of Africa are found in Madagascar. The equatorial facies on the East Coast is characterized by a high transmission all year long. In the tropical facies on the West Coast transmission is seasonal (7 months at least). In both areas, malaria is stable and the inhabitants acquire a high immunity before the age of ten; most of the severe cases touch children below 10. The three vectors can be found but An. gambiae s.s. is dominant. In the exophilic southern facies the transmission is seasonal (two to four months). The only vector is An. arabiensis. Malaria is unstable and severe epidemics occur during the years of high rainfall. All age groups are vulnerable because the population is not immune in the Plateaux facies above 1,000 m., malaria is unstable. Severe epidemics occurred in 1987-1988. The vectors are An. Arabiensis and An. funestus. The occurrence of P. falciparum on the Plateaux seems linked to the development of irrigation of rice farming in the XIXth century. Most of the anopheles breeding places on the Plateaux are dependent on rice cultivation. Urban development has brought the inhabitants of the suburbs in close contact with rice fields. Despite the high number of anopheline bites the number of malaria cases remains by far lower than in the neighbouring rural areas. Regional migrations inside the island bring non-immune populations, from the south and the plateaux, in highly malarious areas of the coast, where the migrants are exposed to high risk. In spite of 40 years of uncontrolled use, chloroquine can still cure most, if not all, of malaria cases. Control measures appropriated to the different areas of Madagascar are discussed.