Malaria Spread in the U.S. for the First Time Since 2003, CDC Says

Five infections caught locally in Florida and Texas have prompted health alerts from state and federal agencies

A close-up of a mosquito biting a person's skin with a solid blue background
Female Anopheles mosquitoes infected with the parasite that causes malaria can spread the disease to humans through a bite. Smith Collection / Gado via Getty Images

Five new cases of malaria transmitted within the United States have raised alarm bells among health officials, according to an advisory from the Centers for Disease Control and Prevention (CDC).

While around 2,000 people in the U.S. are diagnosed with malaria every year, these cases have been contracted when people are traveling abroad. But these five individuals had not recently traveled outside the country, which suggests they contracted the disease locally. The last time someone caught malaria in the U.S. was in 2003, per the CDC.

Four of the cases were in Sarasota County, Florida, and all four people have recovered, according to an advisory from the Florida Department of Health. A Texas resident who spent time working outside was also diagnosed, according to health advisory from the Texas Department of State Health Services.

Malaria is transmitted via bites from female mosquitoes of the genus Anopheles that have been infected with a disease-causing parasite. Malaria is not contagious and cannot be spread from person to person.

In 2021, there were around 247 million cases of malaria worldwide, and an estimated 619,000 people died from the disease, according to the World Health Organization (WHO). Around 95 percent of cases occur in Africa, and more than half of malaria deaths in 2021 were concentrated in four countries: Nigeria, the Democratic Republic of the Congo, Tanzania and Niger. Most deaths are in children under the age of five. Disruptions in controlling malaria caused by the Covid-19 pandemic have led to a rise in cases and deaths in the past couple of years.

Of the roughly 2,000 annual cases in the U.S., around 300 people experience severe disease, and five to ten people die, according to the CDC. Signs of malaria include fever and flu-like symptoms, such as shaking, chills, headaches, muscle aches and fatigue. In severe cases, the disease can cause kidney failure, seizures, mental confusion, coma and death.

The five recent infections are linked to a species of parasite called Plasmodium vivax, which is less likely to cause severe disease than some other Plasmodium species, according to the CDC’s health alert.

People typically begin to feel sick between ten days and four weeks after infection, though on occasion, symptoms might not start for as long as one year. For infections with two species of parasite, including P. vivax, the parasite can remain dormant for up to four years after the person is bitten. Infections caused by these parasites can also relapse, even after months or years without symptoms.

Cases of malaria could rise in the U.S. this summer, as international travel returns to pre-pandemic levels. While malaria can’t spread between people, female Anopheles mosquitoes that bite infected humans can contract the disease and spread it when they bite others.

Malaria used to be widespread in the U.S., but officials used the insecticide DDT to kill mosquitoes and eliminate the disease in the 1950s, per Vox’s Keren Landman.

Malaria spreads in warm and wet environments: The disease-causing parasites need warm temperatures to survive inside the mosquitoes, and the mosquitoes need water to reproduce. By warming the planet, climate change could increase the range where disease-carrying mosquitoes can thrive, writes ABC News’ Riley Hoffman, Nicole Wetsman and Teddy Grant.

“The presence of competent mosquitoes and warmer temperatures in the Southeast will likely lead to additional cases in the coming months and years,” John Brownstein, an infectious disease epidemiologist at Boston Children’s Hospital, tells ABC News. “Future invasion of new mosquitoes, coupled with potential climate change effects, could significantly expand the malaria risk.”

Residents can prevent mosquitoes from multiplying and reduce the risk of getting bitten by draining standing water, using repellent and covering doors, windows and skin—especially during the times when mosquitoes are most active, at dawn and dusk.

The CDC recommends learning about the health risks of places you’re traveling to and the precautions you can take, as well as talking to your health care provider about medicines that may protect you from malaria while abroad.

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