9.15 Malaria

Abstract

Although malaria remains a major public health hazard in many low- and middle-income countries, the overwhelming problems with malaria are in the high-transmission areas of Africa where everyone receives infectious bites every day. One consequence of this high transmission is that clinical malaria in children differs from other parts of the world; it strikes abruptly and kills in 18–72 h. A second consequence is that standard vector control methods effective elsewhere have less impact on reducing malaria disease.The main malaria control methods have been vector control and antimalarial drug treatment. The most important vector control method has been residual insecticide spraying in households that kill vectors when, after a blood meal, they rest on a sprayed wall. The use of dichlorodiphenyltrichloroethane (DDT) in this fashion was dramatically successful in many parts of the world. But then, problems with insecticide resistance and ecological damage (from use in agriculture) led to widespread breakdowns of these control efforts. In most of Africa, vector control by residual insecticides has never been an option because of transmission rates many times more than elsewhere in the world. Until recently, the only control method in Africa has been antimalarial treatment of symptomatic individuals.The use of chloroquine for treatment of malaria was highly successful for decades with low cost and negligible adverse reactions. However, with the emergence and spread of drug-resistant Plasmodium falciparum malaria throughout the world, combination therapy with artmesinin is now universally recommended despite its cost.Malaria is the most intense stimulator of the human immune system known; all immunologic defence systems are activated with massive production of antibodies, cellular immune responses, and cytokine cascades. Although malaria parasites have evolved complex mechanisms of evasion, the overwhelming evidence is that humans do develop protective immune responses. Effective vaccines should be possible and have been expected for decades, but to date none has been sufficiently effective. With recent progress, however, more than 40 candidate vaccines are currently undergoing clinical trials.New malaria control approaches are becoming much more widely used: Insecticide-treated bed nets; intermittent preventive therapy for infants, sick children, and pregnant women; and immediate treatment at home can effectively reduce child mortality even in high-transmission areas.