Malaria is the most important parasitic infection that causes disease in humans. More than a million persons, mostly children, die each year from malaria. It is also one of the most common causes of fever in returned travelers and recent immigrants from malaria-endemic areas.
Malaria is primarily caused by infection with 1 of 4 Plasmodium species: Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae. Occasionally human infection with a monkey malaria parasite, such as P. knowlesi, occurs. Treating malaria appropriately requires knowledge of the infecting species, the likely location in which the infection was acquired, and the geographic patterns of drug resistance. Figure 198.1 shows the worldwide distribution of malaria. When there is any doubt about the infecting species, the clinician should treat for the worst-case scenario, chloroquineresistant P. falciparum (CRPF) malaria. Malaria caused by P. vivax and P. ovale may leave dormant forms, hypnozoites, in the liver after the blood phase has been eradicated. Thus, treatment of these two infections requires eradication of the erythrocytic phase followed by a second drug to eradicate the liver phase (terminal prophylaxis).
CLINICAL ASPECTS
Because death from malaria can occur within several days of the onset of symptoms, it is necessary to consider a febrile illness in a patient from a malarious endemic area to be a medical emergency. This is particularly so when symptoms begin within the first 2 months of arrival because more than 90% of those with malaria caused by P. falciparum present within this time.