Malaria Transmitted Inside the United States for the First Time in 20 Years

Jennifer Middleton, MD, MPH
Posted on July 17, 2023

In the last 20 years, the only cases of malaria diagnosed in the United States have been in people returning from a malaria-endemic country who were infected there. The U.S. Centers for Disease Control and Prevention (CDC), however, recently issued a health advisory regarding seven cases of malaria transmitted by mosquitoes inside the United States. Presumably, those individuals were infected by mosquitoes who had previously bitten an infected returning traveler. Malaria can spread—and be fatal—if not promptly diagnosed, and U.S. family physicians need to keep it in the differential for people presenting with nonspecific viral illnesses.

Malaria is spread by the bite of the Anopheles mosquito. Because its symptoms, including fever, chills, muscle aches, headaches, and fatigue, are more commonly caused by other illnesses in the United States, physicians need to maintain a high index of suspicion. Most of us, I suspect, know to suspect malaria in a returning traveler with a fever, but malaria’s presentation can be delayed by months—or can even be entirely asymptomatic. Diagnosing malaria can be challenging, and concerned physicians can contact the CDC Malaria Hotline for Healthcare Professionals for guidance. Timely malaria treatment benefits both the patient and the community by limiting its spread.

Six of the recent cases in the United States are in Florida, with the seventh case in Texas. Although the CDC stresses that “the risk of locally acquired malaria remains extremely low in the United States,” we can counsel patients who are concerned about malaria that insect repellent along with long sleeves and pants can reduce the risk of transmission. The current media interest in malaria can also serve as a prompt to counsel patients about reducing their risk for the more common arthropod-borne illnesses in the United States. This 2015 AFP article on “Advice for Protection Against Mosquitos and Ticks” provides additional guidance.

The CDC is advising physicians to “[c]onsider the diagnosis of malaria in any person with a fever of unknown origin, regardless of international travel history, particularly if they have been to the areas with recent locally acquired malaria.” Family physicians can ensure their malaria knowledge is current by reviewing the 2022 AFP article on “Malaria: Prevention, Diagnosis, and Treatment.” The CDC website has extensive information on malaria, and an AFP By Topic on Travel Medicine is available as well.