A Traveler's Fever

Roberta Capp, MD; Natan Noviski, MD


December 11, 2017


This case is an example of malaria caused by Plasmodium falciparum. In the context of the patient's recent travel to Nigeria and presentation with fever, malaria was strongly suspected. The patient's blood smear was notable for 15% parasitemia, most likely P falciparum (as evidenced by the circles within some of the red blood cells in the smear in Figure 2).

Figure 2.

The other laboratory findings, such as the thrombocytopenia and elevated bilirubin level, correlated with the disease burden. The elevated creatinine value was also noted, because this finding is sometimes seen in more aggressive cases of the disease; however, this usually resolves with time.

Worldwide, approximately 300-500 million new cases of malaria are recorded annually.[1] Malaria is the most deadly vector-borne illness in the world, causing 3.5-5 million deaths annually. On average, 40% of the 50 million people who travel from industrialized to developing countries each year report some illness associated with their travel. Approximately 1200 cases of malaria are reported each year in the United States among travelers; therefore, malaria should be considered as a possible cause of fever in the returning traveler.

Malaria results from an infection caused by any of the following 5 protozoa of the genus PlasmodiumP falciparumP vivaxP ovale, P knowlesi, and P malariae.[2] Transmission of the parasite occurs via the bite of the Anopheles mosquito. Once the protozoa are injected into the bloodstream, they enter the hepatic cells and reproduce; eventually, the hepatic cells erupt and release more protozoa into the host's circulation. These parasites then remain in the bloodstream, periodically invading erythrocytes, causing hemolysis, and infecting new red blood cells.

The incubation period tends to be 9-18 days for P falciparumP vivax, P ovale, and P knowlesi, but P malariae has an incubation period of 18-40 days. The most common parasites seen in the United States are P falciparum, which are often found in travelers returning from sub-Saharan Africa, and P vivax, which are found in those returning from Asia, Eastern Europe, and Latin America.

The clinical presentation varies between these two parasites. P falciparum often causes symptoms within the first month after the travel period and can be fatal; of patients infected with P vivax, 50% have symptoms within 1 month after travel, and approximately 2% have symptoms 1 year after exposure. Most patients infected with either parasite are usually symptomatic within the first 3 months after they return to the United States.


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