Why is the US Army using mefloquine prophylaxis in Afghanistan? Mark Rowland, London School of Hygiene and Tropical Medicine 24 February 2008 With such a high rate of adverse reactions to mefloquine propylaxis it makes little sense to continue with this policy in Afghanistan. Malaria in Afghanistan is predominantly caused by vivax (>85%) with 15% at most caused by falciparum (based on trends of reporting based on microscopy at clinics run by reputable NGOs). Of all febrile illness recorded at clinics and diagnosed by blood film only 25% is malaria. This means that falciparum malaria represents less than 5% of all febrile illness. Falciparum is also highly seasonal, occurring during the months of July to October, and occurs only in lowland non-arid areas. If prophylaxis is to be prescribed at all it makes more sense to use chloroquine to which vivax is still susceptible. To continue with a blanket policy of mefloquine prophylaxis when the majority of soldiers will never be based in malaria endemic areas or at times of the year when falciparum is not transmitted, makes little sense when the risks are balanced against the frequency of adverse reactions to mefloquine and the effect these may have on soldier performance under operational conditions. Competing interests None. Mark Rowland managed a malaria control programme in Afghanistan from 1991 until 1999 and still runs malaria research projects in the country.