Malaria

Malaria, a protozoan infection of red blood cells transmitted by blood-feeding female anopheline mosquitoes, is often the most common cause of fever in the tropics. Malaria infections are caused by Plasmodium falciparum, P. vivax, P. malariae, P. ovale, P. knowlesi, and rarely some other simian parasites. In Africa, P. falciparum predominates, whereas in Asia and the Americas, P. vivax is now more common. Malaria is diagnosed by microscopy of suitably stained thick and thin blood smears or by rapid diagnostic tests, which detect parasite antigens in the blood. The clinical manifestations of malaria are fever, anaemia, and splenomegaly. Most deaths result from P. falciparum infections in African children. Severe falciparum malaria may cause coma (cerebral malaria), acidosis, severe anaemia, renal dysfunction, and pulmonary oedema. Uncomplicated malaria is treated with artemisinin combination treatments. P. vivax, P. malariae, P. ovale, and P. knowlesi infections may also be treated with chloroquine. P. vivax and P. ovale malaria also require ‘radical treatment’ with primaquine to eliminate the persistent liver forms (hypnozoites) which cause later relapses. The key elements of malaria control are effective drug treatment, deployment of insecticide-treated bed-nets, and where appropriate, indoor residual insecticide spraying. In higher-transmission areas, intermittent preventive treatments in pregnancy and seasonal malaria chemoprevention in children <6 years are deployed. The main threats to malaria control are increasing antimalarial drug resistance, increasing insecticide resistance, institutional ineffectiveness and declining political will. The RTS,S P. falciparum malaria vaccine, which provides moderate short-term protection has recently been approved. The global burden of malaria has been reduced substantially in the past 20 years but over the past 6 years progress in Africa has stalled for reasons that are not clear.