Malaria, a protozoan disease transmitted by the bite of the Anopheles mosquito, is one of mankind’s most feared and serious afflictions. It is a leading cause of morbidity and mortality in many tropical areas of the world, especially in Africa. Approximately 55% of the world’s population is exposed to the infection, which exerts its toll mainly on the young and the pregnant. Malaria is endemic or sporadic throughout most of the tropics and subtropics below an altitude of 1500 m, excluding the Mediterranean littoral, the United States, and Australia. Malaria is perhaps the most significant disease acquired through international travel to the tropics.
Five species of the genus Plasmodium infect humans: Plasmodium vivax, Plasmodium ovale, Plasmodium malariae, Plasmodium falciparum, and Plasmodium knowlesi. In 2016, there were an estimated 216 million cases of symptomatic malaria worldwide (88% of which occurred in Africa), with about 445,000 deaths, 90% of which occurred in Africa, with nearly 77% of those occurring in young children.1 The great majority of malaria deaths are due to P. falciparum infections, although both P. vivax and P. knowlesi can also cause fatal disease. P. knowlesi is a zoonosis. Macaques (old world monkeys) are the natural host, and the transmitting mosquito’s habitat is limited to the forest fringe—a fact that may limit the spread of this species of parasite.2
The global incidence of malaria (both cases and deaths) has decreased dramatically in recent years. In many countries, however, transmission has remained unchanged or even increased.1 Obstacles to successful reduction of malaria worldwide include human factors (poverty, war, inadequate international cooperation), capacities of the mosquito vector (changing temperatures, insecticide resistance), and parasite characteristics (antimalarial drug resistance).
Malaria transmission occurs in large areas of Central and South America, the Caribbean, sub-Saharan Africa, the Indian subcontinent, Southeast Asia, the Middle East, and Oceania. Certain species may predominate in a given geographic area.3 For example, P. vivax is more common in the Indian subcontinent, whereas P. falciparum is the most prevalent form in Africa, Haiti, and New Guinea. P. knowlesi has been found in several countries in southeast Asia, including Malaysia, Myanmar (Burma), Thailand, the Philippines, and Singapore.4
The risk of contracting malaria varies considerably between regions. In 2014, the Centers for Disease Control and Prevention reported 1724 cases of malaria among persons in the United States.3 Of 1605 imported cases where the region of acquisition was known, 1383 (82%) were acquired in Africa (70% of these in West Africa), 160 (9.5%) in Asia (62% of these in India), and 54 (3.4%) in Central and South America and the Caribbean. P. falciparum accounted for 66% and P. vivax for 13% of all cases (although in many cases, the parasite species was not identified). Thus >60% of all cases of malaria identified in the United States in 2014, including the majority of cases ...