Mefloquine-resistant strains of Plasmodium falciparum in Madagascar: impact on tourists and public health

Although the national policy for malaria control in Madagascar is to use ch loroquine as the first line of treatment, mefloquine has been and is recomm ended to travellers to the country, both for malaria prevention and cure. T he in-vitro susceptibility of Plasmodium falciparum to mefloquine was there fore assessed during a prospective surveillance study in various areas in M adagascar, including the tourist sites of Nosy-be and Sainte Marie. Of the 254 isolates of P. falciparum successfully tested, 232 (90.9%) were sensitive to mefloquine, 12 (4.7%) showed decreased susceptibility (40 nM < IC50 < 50 nM), and 10 (3.9%) were resistant (IC50 > 50 nM). Five (50%) of the resistant strains and nine (75%) of those with decreased susceptibility were from coastal areas or the two tourist sites. The drug pressure that c ould have induced the resistance observed could therefore be related to the donation of antimalarials, such as mefloquine, by tourists to local popula tions. The residents of the coastal areas take any donated drugs as self-me dication, ignoring recommended doses and durations of treatment. This situation has two main consequences: (1) there is an urgent need to co ntrol the abusive and incorrect use of antimalarial drugs in Madagascar, to safeguard the effectiveness of chemotherapy in the future; and (2) these i ncreases in resistance compromise the efficiency of the antimalarial chemop rophylaxis currently recommended to tourists. The use of mefloquine can no longer be considered as a guarantee of protection against malaria in coasta l areas and other sites frequented by tourists.