Malaria

Background
Malaria, which predominantly occurs in tropical areas, is a potentially life-threatening disease caused by infection with Plasmodium protozoa transmitted by an infective female Anopheles mosquito vector. Individuals with malaria may present with fever and a wide range of symptoms.

The 4 Plasmodium species known to cause malaria include Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae. A fifth species, Plasmodium knowlesi, has recently been identified as a clinically significant pathogen in humans. Timely identification of the infecting species is extremely important, as P falciparum infection can be fatal and is often resistant to standard chloroquine treatment. In some cases, individuals with malaria are infected with multiple Plasmodium species. P falciparum and P vivax are responsible for most new infections. Each Plasmodium species has a defined area of endemicity, although geographic overlap is common. Species can usually be distinguished by morphology on a blood smear. P falciparum is distinguished from the rest of plasmodia by its high level of parasitemia and the banana shape of its gametocytes.

Malaria in travelers typically manifests weeks after the individual leaves the endemic area. Presentation more than 4 weeks after returning from the endemic area is unusual. In some individuals, disease manifests months or years later, usually due to the presence of P vivax or P ovale hypnozoites, which can remain dormant in the liver and reactivate years after infection. Relapse with P vivax or P ovale infection is rare more than 5 years after initial infection. Because symptomatic delay is common, history of even a remote exposure to an endemic area should be elicited. Symptoms of malaria are nonspecific, and, because timely diagnosis and treatment are necessary, malaria should be considered in all patients from tropical areas who present with fever. Read more »