Few diseases match malaria in historical and global mortality. Within the United States, though the vast majority of cases are in the armed forces, nearly all civilian cases of malaria enter the health care system through the emergency department. Here, the risk of malaria is highest in returning travelers from endemic regions, especially those who failed to take chemopro-phylaxis, and who present with fever and systemic symptoms. Notably, the diagnosis is missed in 40% of United States fatal cases.¹

Given that delay to diagnosis and initiation of treatment may lead to death, emergency physicians should be able rapidly to diagnose malaria and initiate appropriate therapy.

Pathophysiology and Epidemiology

Malaria is caused by approximately 10 species of the Plasmodium protozoa. The five most common are P. falciparum, P. vivax, P. knowlesi, P. ovale, and P. malariae. The parasite is transmitted through the bite of the Anopheles female mosquito, with P. falciparum responsible for nearly all mortality. The patient is initially asymptomatic for

1-2 weeks while the parasite reproduces in the liver. Subsequently, the parasite is released into the bloodstream, where it reproduces within red blood cells until the cells hemolyze. The patient appears jaundiced and develops cyclical fever and systemic complaints. These often begin once the returning traveler has been home already for several days or weeks, but may be delayed for months to years.

The life cycle of the parasite forms the basis of treatment, as both liver and blood stages of the parasite must be eradicated. Dormant liver forms of P. vivax and P. ovale lead to relapse months to years later, despite prophylaxis and treatment.

Evaluation and Diagnosis

Returning travelers with fever should be questioned regarding travel to endemic regions, use of malaria prophylaxis medications, and the onset and periodicity of fevers. A thorough review of systems should be obtained.