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Malaria, a protozoan disease transmitted by the bite of the Anopheles mosquito, is one of mankind’s most feared and serious afflictions that causes greater morbidity and mortality than any other human disease, 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 U.S., and Australia.

Malaria is perhaps the most significant disease acquired through international travel to the tropics. Five species of the genus Plasmodium infect humans: P. vivax, P. ovale, P. malariae, P. falciparum, and a new species P. knowlesi. Annually, >500 million persons develop malaria, and >1 million persons die.1,2 The P. falciparum parasites alone kill in Africa 1% to 2% of children and are responsible for at least 1 million deaths each year.

The incidence of malaria is increasing despite aggressive worldwide eradication efforts. Not only is the mosquito vector becoming less susceptible to a variety of insecticides, but P. falciparum—the parasite responsible for the most deadly form of malaria—is becoming more resistant to antimalarial medications.

Malaria, especially disease due to P. falciparum, is a medical emergency in any nonimmune host. The mortality rate of severe malaria is anywhere from 10% to as high as 50% if untreated. The early signs of malaria are nonspecific, and malaria can mimic other infections. Failure to diagnose an infection rapidly and failure to use antimalarial agents to which the individual strain is susceptible can result in early death. A diagnosis of malaria must be considered in any person returning from the tropics with an unexplained febrile illness.

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 and in Central America, whereas P. falciparum is the most prevalent form in Africa, Haiti, and New Guinea. P. knowlesi has been found in Malaysia, Myanmar (Burma), Thailand, the Philippines, and Singapore.4

The risk of contracting malaria varies considerably between regions. In 2007, the Centers for Disease Control and Prevention (CDC) reported 1505 cases of malaria among persons in the U.S.5 Of 1155 imported cases where the region of acquisition was known, 744 (64%) were acquired in Africa (nearly 75% of these in West Africa), 253 (22%) in Asia (nearly 60% of these in India), 99 (9%) in the Caribbean and Central America, 27 (2%) in Oceania, and only 20 (2%) in South America. P. falciparum accounted for 62%, whereas P. vivax accounted for only 29% of all cases. Thus, almost half of all cases of malaria, including the majority of cases due to P. falciparum,...

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