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 chloroquine as the first line of treatment, mefloquine has been and is recommended to travellers to the country, both for malaria prevention and cure. The in-vitro susceptibility of Plasmodium falciparum to mefloquine was therefore assessed during a prospective surveillance study in various areas in Madagascar, 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 could have induced the resistance observed could therefore be related to the donation of antimalarials, such as mefloquine, by tourists to local populations. The residents of the coastal areas take any donated drugs as self-medication, ignoring recommended doses and durations of treatment. This situation has two main consequences: (1) there is an urgent need to control the abusive and incorrect use of antimalarial drugs in Madagascar, to safeguard the effectiveness of chemotherapy in the future; and (2) these increases in resistance compromise the efficiency of the antimalarial chemoprophylaxis currently recommended to tourists. The use of mefloquine can no longer be considered as a guarantee of protection against malaria in coastal areas and other sites frequented by tourists.