Locally acquired malaria cases identified in the United States

Health advisory

July 17, 2023

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Be aware that locally acquired malaria cases (Plasmodium vivax) have been identified in Florida (4) and Texas (1) within the last 2 months.
Consider 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.
Routinely obtain a travel history and consider malaria in a symptomatic person who traveled to an area with malaria in the weeks to months preceding symptom onset.

Order microscopic examination of thin and thick blood smears, and a rapid diagnostic test (RDT) if available, to diagnose malaria and confirm species.

If blood smears or RDT are positive and species determination is not available, antimalarial treatment effective against chloroquine-resistant P. falciparum must be initiated immediately.
Species determination is important because P. vivax and P. ovale can remain dormant in the liver and require additional anti-relapse treatment; failure to treat the dormant hepatic parasites may result in chronic infection with relapsing episodes.

Be aware of treatment recommendations for malaria, which vary by species and severity. Please refer to CDC's Malaria Diagnosis and Treatment Guidelines for U.S. Clinicians for specific detailed instructions.

Malaria is a medical emergency. If not diagnosed and treated promptly, illness may progress to severe disease, a life-threatening stage, where mental status changes, seizures, renal failure, acute respiratory distress syndrome, and coma may occur. An algorithm for diagnosis and treatment of malaria is available (PDF).
Artemether-lumefantrine (Coartem®) is the preferred initial treatment of uncomplicated P. falciparum or unknown species of malaria acquired in areas of chloroquine resistance. Atovaquone-proguanil (Malarone®) is another recommended option. P. vivax infections acquired from regions other than Papua New Guinea or Indonesia should initially be treated with chloroquine (or hydroxychloroquine).
IV artesunate is the first-line drug for treatment of severe malaria in the United States.

Be aware that CDC malaria clinicians are on call 24/7 to provide advice to healthcare providers following infectious disease consultation. Further information can be found by contacting the CDC.
Discuss travel plans with patients. Prescribe a CDC-recommended malaria chemoprophylaxis regimen and discuss mosquito bite prevention for those traveling to an international area with malaria.

Chemoprophylaxis is not needed domestically at this time.

Report suspected cases of locally acquired malaria to Public Health 206-296-4774 within 3 business days.

CDC and local health jurisdictions have identified five cases of malaria (Plasmodium vivax) in Florida and Texas in persons with no international travel history. There is no evidence to suggest the cases in the two states are related. In Florida, four cases within close geographic proximity have been identified, and active surveillance for additional cases is ongoing. Mosquito surveillance and control measures have been implemented in the affected area. In Texas, one case has been identified, and surveillance for additional cases, as well as mosquito surveillance and control, are ongoing. All patients have received treatment and are improving. Locally acquired mosquito-borne malaria has not occurred in the United States since 2003, when eight cases of locally acquired P. vivax malaria were identified in Palm Beach County, FL.

The risk of locally acquired malaria remains extremely low in the United States. However, Anopheles mosquito vectors, found throughout the United States, are capable of transmitting malaria if they feed on a malaria-infected person. The risk is higher in areas where local climatic conditions allow the Anopheles mosquito to survive during most of or the entire year and where travelers from malaria-endemic areas are found. Prompt diagnosis and treatment of people with malaria can prevent progression to severe disease or death and limit ongoing transmission to local Anopheles mosquitos. Individuals should take steps to prevent mosquito bites and control mosquitos at home to prevent malaria and other mosquito-borne illnesses. There have been no reported cases of locally acquired malaria in Washington state at this time.

Almost all cases of malaria in the United States are imported and occur in people traveling from countries with malaria transmission, many from sub-Saharan Africa and South Asia.