malaria parasite

Colorized electron micrograph showing malaria parasite (right, blue) attaching to a human red blood cell. The inset shows a detail of the attachment point.

In June and July, eight locally acquired cases of malaria were diagnosed in the U.S.—seven in Florida and one at the southern tip of Texas. Cases in the two states appear to be unrelated, and all patients are recovering. In both geographic areas, it’s likely that malaria in people with travel-related cases was transmitted by local (U.S.) mosquitoes to the people who developed the locally acquired cases.

Malaria was endemic in this country until the early 1950s, when mosquito control programs and public health campaigns brought the disease under control. Since that time, virtually all cases in the U.S—now at almost 2000 per year—have been travel related.

Malaria transmission.

Malaria is caused by several species of the Plasmodium parasite, transmitted by the bite of a female Anopheles mosquito infected by the parasite. In less than one percent of cases, transmission occurs congenitally or via transfusion, organ transplant, or unsafe needle sharing.

Why it matters.

If you’re not one of the people infected in Florida or Texas this summer, or a nearby resident, why should you care about malaria?

  • Travel-related cases are increasing. The number of imported U.S. cases has steadily increased since the early 1970s. Most U.S. cases occur during the summer and fall. With increased post-COVID travel; a warming and in some locales, wetter climate; and plateauing or decreased funding for malaria control programs in many countries, conditions are ripe for an increase in malaria across the globe.
  • Malaria symptoms are nonspecific. Early symptoms include fever, chills, headache, muscle aches, fatigue, and sometimes GI symptoms. The incubation period varies widely, but in most cases, symptoms occur within a month after infection. If the disease progresses without treatment, the infected person may experience impaired consciousness, seizures, shock, acute respiratory distress syndrome, acute kidney injury, abnormal bleeding, jaundice, and death.
  • Many medical facilities don’t routinely stock diagnostic tests and drugs for malaria.   The CDC emphasizes that “malaria is a medical emergency” and calls for diagnosis and treatment within 24 hours. Prompt treatment can prevent progression to severe disease and limit ongoing transmission.

Staff in hospitals and emergency facilities need rapid access to microscopic examination of a blood smear by an experienced technician to determine the Plasmodium species and parasite load. PCR tests for malaria also are available, but PCR testing usually takes longer to set up than microscopy. This summer’s cases were caused by P. vivax, which usually results in less severe illness.) Newer rapid diagnostic tests for malaria are becoming more sensitive, but rapid tests are not able to identify the Plasmodium species or parasite load.

The agents most commonly used for malaria treatment in the U.S. are artemether-lumefantrine (Coartem) for uncomplicated cases, and IV artesunate for severe malaria.

The CDC urges all medical facilities to ensure that staff consider the diagnosis of malaria in cases of a fever of unknown origin and to arrange for rapid access to both accurate diagnostic tests and malaria drugs in order to quickly manage suspected cases of malaria. CDC resources for clinicians include:

Personal preventive measures.

If you plan to travel internationally, consult the CDC’s Yellow Book for detailed and up-to-date information about health and safety measures. If traveling to areas where malaria is endemic, your level of risk depends on your own health, your itinerary, your accommodations (screens? air conditioning? neither?) and modes of travel, and the season. Insect repellents and bed nets will usually be necessary, along with taking one of several possible medications as a malaria preventive. It’s safest to acquire medications in the U.S. before travel, because “fake” antimalaria drugs and drugs of dubious quality are the norm in some countries.