[Drug resistance of Plasmodium falciparum along the borders of the highlands in Madagascar: outlook for a national control program].

Resistance of Plasmodium falciparum to chloroquine was first suspected in Madagascar in 1975 and later confirmed in vivo and in vitro. During the period from 1985 and 1990, the network of public health monitoring stations reported that 1% of the population living on the central Highlands of Madagascar died of malaria. Thereafter the National Malaria Control Program achieved good success by spraying homes with insecticide and reorganizing distribution of chloroquine in all villages. However data recorded between 1996 and 1998 indicates that, after four years of widespread chloroquine use, resistance to amino-4-quinolones is progressing in Madagascar. The tests described in this report were performed on patients with documented malaria included in cohorts and followed year round by a physician. The three villages studied were located along the borders of the highlands between the plateaus and coastal areas. In vivo tests showed that the incidence of chloroquine resistance was 0% in Mahakary, 32% in Ankazobe and 30% in Saharivo. Clinically, however, treatment was unsuccessful in only 16% and 8% of cases respectively. In vitro tests demonstrated chloroquine sensitivity in 79% of the 153 strains tested. No resistance to quinine or halofantrine was observed. In vitro tests indicated an onset of resistance to mefloquine. Although the success rate of chloroquine treatment is nearly 80%, spread of strongly chloroquine-resistant strains is a risk especially in subjects with mild immunity to malaria.