College Health May Be Full of Surprises: International Travelers and Tropical Diseases

THREE CAUSES OF FEVER IN RETURNING TRAVELERS
There are numerous etiologies for fever in the returning traveler. Factors such as location of travel, length of stay, dates of travel, date of symptom onset, risk activities undertaken, and reason for visit help determine the cause of illness.⁵ Two of the most commonly encountered conditions causing illness in the febrile traveler are dengue fever and malaria. Additionally, chikungunya is an emerging health concern in the US that has received increased attention following a massive outbreak in the Caribbean (which affected many American travelers) in 2013. In a retrospective study of patient records from 462 febrile adults who traveled to malaria-endemic areas, Siikamäki and colleagues found that every fourth febrile returning traveler had an illness that was potentially life-threatening.⁶ Understanding the possible causes of febrile illness in travelers can aid the clinician in diagnosing and correctly treating potentially life-threatening conditions.

Malaria
Malaria is a mosquito-borne illness transmitted in humans by female Anopheles mosquitoes.⁷ It is caused by infection with the protozoal parasites Plasmodium falciparum, P vivax, P ovale, P malariae, and occasionally other Plasmodium species.⁸ An infected female Anopheles mosquito transmits the parasite into a human host through a bite. The most severe form of human malaria, which can be fatal, is caused by P falciparum. Falciparum and vivax malaria are the most common forms of malaria worldwide.⁸

According to the WHO, there were an estimated 214 million clinical episodes of malaria worldwide, and malaria was the cause of 438,000 deaths, in 2015.⁹ In 2012, the CDC received reports of 1,687 cases of malaria in the US.⁸ The number of malaria cases has been steadily increasing since 1973.⁸ Figure 2 shows the number of malaria cases diagnosed in each state in 2012. The data demonstrate that malaria is the primary cause of death in travel-related fever. Malaria is also the most common single reason for travel-related fever without findings on exam or workup.

Dengue fever
Dengue is a mosquito-borne disease (transmitted by an infected Aedes mosquito) and is caused by four types of flaviviruses (DENV-1, DENV-2, DENV-3, DENV-4).¹⁰ It is the most common arboviral disease in humans.¹¹ In 2009, the WHO revised its dengue categories to include dengue, dengue with warning signs, and severe dengue.^12,13 Previously, the categories included dengue fever, dengue hemorrhagic fever, and dengue shock syndrome.

Dengue is endemic throughout the tropics and subtropics and is a leading cause of febrile illness among travelers returning from the Caribbean, South America, and South and Southeast Asia.¹⁴ There has been a 30-fold increase in dengue fever in the past 50 years.¹⁰ This illness is present in more than 100 countries; in the US, outbreaks have occurred in Florida, Hawaii, and along the Texas-Mexico border.¹⁴

Chikungunya
Chikungunya virus (CHIKV) is an arbovirus that is transmitted by Aedes mosquitoes (Aedes aegypti and Aedes albopictus).¹⁵ The term chikungunya is derived from a word in the Swahili and Maconde language that means “the one that is folded.”¹⁶ This description refers to the severe arthralgias that can cause a hunched-over gait in the patient with chikungunya.

Chikungunya historically has not had a significant impact in the Americas or Europe. However, more than one million suspected cases of chikungunya have been reported in the Americas since October 2013.¹⁶ Most cases of CHIKV infection diagnosed in the US have occurred in travelers; however, there have also been documented cases of local transmission of the virus.¹⁷ Local transmission occurs when the ill returning traveler unknowingly spreads disease, with the aid of the mosquito vector, upon return to the US.

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