Malaria is a leading cause of childhood morbidity and mortality worldwide. The burden of this disease is largely borne by children in sub-Saharan Africa. Approximately 60% of clinical cases, and more than 75% of the greater than 1 million annual deaths from malaria occur in this region, mostly in children younger than 5 years.1,2 According to a survey, one in five childhood deaths in sub-Saharan Africa is caused by malaria.3 In the United States, local malaria transmission, which was once endemic, has been extremely rare since the 1950s.4 However, American physicians continue to encounter patients with malaria, mostly immigrants, refugees, returned travelers, and military personnel, who acquired their infections in endemic areas. An average of 1200 malaria cases and 13 related deaths occur in the United States every year.4 Most of the cases are imported, most are caused by Plasmodium falciparum, and most are acquired in Africa.4
Malaria is a parasitic infectious disease that has been in existence for centuries. The name “malaria” is of Italian origin, meaning “bad air,” reflecting the belief in medieval times that it was caused by exposure to foul air in swamps and marshes. This is true to some extent, because the mosquito vector breeds well in warm, humid environments. As a result, the disease is highly prevalent in tropical and subtropical areas, including sub-Saharan Africa, the Indian subcontinent, South-East Asia, and South America (Figure 66–1). Malaria is caused by the parasitic protozoan Plasmodium, among which there are approximately 120 species that infect mammals. Human malaria is caused by four Plasmodium species: P. falciparum, Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae. P. falciparum is prevalent in the tropics and subtropics, specifically in sub-Saharan Africa, the Indian subcontinent, South-East Asia, and the Western Pacific.5 It accounts for the majority of all human Plasmodium infections worldwide. P. vivax is commonly found in Asia, South America, parts of Europe, North Africa the Middle East, and the Western Pacific, particularly in Papua New Guinea.5 It is rarely found in sub-Saharan Africa, and is virtually nonexistent in West Africa. P. malariae occurs sporadically in all malaria endemic areas, but is largely restricted to sub-Saharan Africa and the Western Pacific.6P. ovale is the rarest of all 4 species, and is found mainly in West Africa and the Western Pacific.6 The definitive vector is the female Anopheles mosquito, which requires a blood meal in order to lay eggs.
Global malaria risk distribution. (With permission from the World Health Organization.)
The life cycle of Plasmodium takes place in both the human host and mosquito vector (Figure 66–2): (1) The female Anopheles mosquito takes a blood meal, during which it injects sporozoites (human infective stage) into the human host. The sporozoites pass through the bloodstream into the ...