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  • Writer's pictureP.K. Peterson

Homegrown Malaria in the United States: Should You Worry?

“First US Malaria Cases in 20 Years Prompt CDC Advisory.”

- Journal of American Medical Association, July 5, 2023

“Without geography you're nowhere.”

- Jimmy Buffett, American singer-songwriter

In the U.S., malaria is not a “big deal.” Each year, about 2,000 cases of travel-related malaria are reported (usually occurring in people returning from countries where malaria is common). But on June 26, 2023, the Centers for Disease Control and Prevention (CDC) issued a malaria warning after five cases of malaria were identified in the U.S. that were acquired locally (four in Florida and one in Texas). Locally acquired mosquito-borne malaria hasn’t occurred in the U.S. since 2003 when eight cases of Plasmodium vivax malaria were identified in Palm Beach County, Florida. The new cases of locally acquired malaria raise the concern that mosquitoes in Florida or Texas could pick up and transmit the parasite and malaria could become a big deal.

I recently reviewed the topic of malaria in the May 3, 2023 Germ Gems post, “The Latest Buzz on Malaria.” But given all the fuss over the locally acquired cases, I thought a brief update seemed in order.

What me worry? Geography (where an infected person lives) is a powerful risk factor for developing a serious infection. And malaria is a prime example of the paramount importance of geography.

In 2022, an estimated 247 million cases of malaria and 619,000 deaths were reported globally. And statistics from 2021, show that 95% of malaria cases and 96% of malaria deaths were all in Africa, with children under five accounting for 80% of malaria mortalities on the continent.

A key determinant of the course of malaria infection is the species of the parasite causing the disease. Of the five species of Plasmodium that cause malaria in humans, P. falciparum is by far the species that most often causes severe and life-threatening disease. More than 90% of the world’s malaria mortality is attributed to P. falciparum.

While P. falciparum is the deadliest and the most prevalent form of malaria on the African continent, P. vivax is endemic in many countries in the southeast Asia and western Pacific regions. It is also the species responsible for the locally acquired cases in the U.S. P. vivax rarely causes fatal infection, but it accounts for substantial morbidity, mostly associated with recurrent bouts of fever, anemia, and adverse pregnancy outcomes. (The country of origin of the locally acquired cases of P. vivax in the U.S., none of which was fatal, is unknown.)

By July 7, 2023, the number of locally acquired malaria cases in the U.S. had risen to a total of six cases in Florida. Nonetheless, the CDC said that the risk of contracting malaria locally was extremely low for Americans. (I’d say that unless you live in or plan to visit Sarasota County where all the Florida cases occurred, you have a greater risk of being struck by lightning (the odds of being struck by lightning in the U.S. during one's lifetime are 1 in 15,300).

What else is new? Since my May 3, 2003 Germ Gems post on malaria, the World Health Organization (WHO) declared Belize “malaria free”—bringing to 42 the official number of nations and territories that have eliminated malaria. But there are still 85 countries where malaria exists and is transmitted. Thus, we still have a long way to go before malaria is retired to the dustbin of history along with smallpox virus.

While we still face many challenges before malaria is eliminated from the globe, there is good news—in October 2021 the world’s first malaria vaccine was rolled out. And on July 5, 2023 it was announced that the vaccine, which is prioritized for children, will be delivered to 12 African countries later this year. On an even more optimistic note, the WHO, UNICEF, and the Vaccine Alliance (GAVI), expect the manufacturer, Glaxo SmithKline, to produce about 15 million doses per year from 2026 through 2028. Having an effective malaria vaccine is considered a “huge deal” (world-changing by most scientists involved in the fight against this ancient scourge.)

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.

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