[Vector control in the epidemics of the Madagascar highlands]

The Plateau, or more precisely the highlands, cover most of the central part of Madagascar with an altitude higher than 1,000 m. There the climate is tropical with a wet and hot season, from October through April coincident with further outbreaks of malaria. This alternates with a dry season from May through September when the temperature is not favorable to the development of the vectors and the extrinsic cycle of the parasite. The malaria is unstable. The short season of transmission is sometimes amplified by abnormally abundant rain or higher than average temperatures. The population can hardly develop self-protection. The epidemics are deadly. The transmission essentially occurs with Anopheles arabiensis, a zoophile species, exophage and occasionally anthropophile and A. funestus anthropophile and endophile. Starting in 1949, a program for fighting malaria was founded on drug prophylaxis and spraying persistent insecticides within the homes. This approach gave spectacular results with a prolonged elimination of the disease, the consequence of which was the establishment of the Zone of Surveillance of the High Plateau (ZSHP). With decreasing efforts of the fight, the transmission progressively resumed starting in 1975 with outbreaks of epidemics. The most deadly outbreak was between 1984 and 1987, marked by an increase of morbidity and mortality. The factors which favored further outbreaks of malaria are listed as follows: 1) a slackening of the surveillance system; 2) the socio-economic context leading to the weakness of the national sanitary system and the inaccessibility of the antimalaria medication for the rural masses; 3) the reappearance of A. funestus, an excellent vector which had been eliminated by the treatments between 1949 and 1960; 4) after the previous elimination, the quasi-total absence of self-protection for the population when subjected to a series of cyclones; 5) movements of nonprotected travellers migrating for agricultural work from the highlands towards the coasts or the slopes which are zones of more stable malaria. Starting in 1988, the Madagascan sanitary authorities, with international and bilateral help, established a strategic approach based on early drug therapy and spraying within the homes with DTT pm 75 at a dose of 2 g/m2. These operations could cover some focalized zones with habitants, numbering 720,000 from 1988 to 1989; 380,000 from 1989 to 1990; 480,000 from 1990 to 1991; and 2,400,000 from 1993 to 1994. The evaluation of the efficacy of these methods in fighting malaria showed spectacular and conclusive results for the epidemiological plan, including less prevalence of the parasite, morbidity and mortality. In addition, there were important impacts on the vectors, including decreases of vector-human contact, residual fauna and longevity.