Malaria is back in the United States. Here’s what you need to know.

Climate change, travel patterns, and a lack of vigilance about mosquitoes all contribute to higher risk.
Aug. 17, 2023
Malaria is not contagious but it is spread by an infected mosquito biting an uninfected person.
Malaria is a disease caused by a parasite that’s transmitted by mosquitoes. The United States has about 2,000 malaria cases a year, nearly all from travelers coming home. But 2023 saw the first locally transmitted cases in a generation. Photo: Getty images.

On June 26, 2023, the U.S. Centers for Disease Control and Prevention issued a health advisory with news that the first locally acquired malaria cases in a generation had been reported in Texas and Florida. Malaria, a disease endemic to the United States from before the country’s founding until the early 1950s, had returned.

Would it establish a foothold again? Dr. Daniel Pastula, a tropical-disease expert and chief of neuro-infectious disease and global neurology at the University of Colorado School of Medicine and Colorado School Public Health, helps answer a few questions about malaria.

What is malaria? Is it viral?

Malaria is a disease caused by a parasite that’s transmitted by mosquitoes – in particular, the Anopheles mosquito. Symptoms of malaria include high fevers, chills and flu-like symptoms.

Are there different types of malaria?

Five malaria parasites infect humans: Plasmodium falciparum, P. vivax, P. ovale, P. knowlesi, and P. malariae. The most dangerous is typically P. falciparum if not promptly treated.

Is malaria contagious? How is it transmitted?

Malaria doesn’t spread directly from person to person, like a cold or the flu. It’s a vector-borne disease, transmitted most often when a mosquito bites someone with malaria and then bites someone without malaria. Because the parasite resides in red blood cells, it can also be transmitted through blood transfusion, organ transplant, shared syringes, or from a mother to an unborn infant.

Are there Anopheles mosquitoes in the United States?

Yes. But the presence of the mosquito is only part of the story, Pastula says.

“You have to have enough Anopheles mosquitoes in the same area where humans are infected with malaria,” he said. “And that’s what we saw in Texas and Florida.”

Where is malaria prevalent?

Malaria is transmitted locally in 87 countries where nearly half the world’s population lives.

Dr. Dan Pastula

How many people die from malaria each year?

The World Health Organization estimates that there were about 247 million cases in 2021, and about 619,000 people died – many of them young children. Most cases and deaths happen in Africa.

Is there are cure for malaria?

There are several treatments for malaria. Treatment depends on the patient and the type of malaria suspected, as drug resistance varies. The earlier the treatment, the better.

Is malaria endemic in the United States?

Not at the moment, though 2023 did see local U.S. malaria transmission – a handful of cases in Florida and one in Texas – for the first time since 2003. The CDC estimates that there are about 2,000 U.S. malaria cases a year, on average. Most happen when the disease comes home with travelers.

Has malaria been a problem in the United States in the past?

Yes. It was among the leading causes of death in the southeastern United States in the 1800s and affected the country’s most populated regions. The CDC is a successor to the U.S. Office of Malaria Control in War Areas, which was established in 1942 to limit malaria and other diseases spread by mosquitoes in the southeastern United States during World War II. The CDC led an aggressive, 13-state mosquito-eradication program starting in 1947. Now-banned DDT was a primary tool in that effort. By the early 1950s, the local spread of malaria had ceased.

Could malaria again become a problem in the United States in the future?

Yes, though probably not like it was in the distant past. Climate change is expanding the range of mosquitoes that transmit malaria through both warming temperatures and increasing rainfall that fills more mosquito breeding sites.

“Typically, the risk of seeing malaria spread locally increases when Anopheles mosquitoes survive during most of or the entire year,” Pastula said.

The continued rise of global travel in an interconnected world adds to the risk, he says, as diseases can spread more easily beyond their historic ranges.

“If we don’t have robust public health and vector control systems, vector-borne diseases may become endemic in areas where they classically weren’t,” Pastula said. “We should be prepared for emerging and re-emerging infections by supporting strong public health surveillance systems, strong vector-control systems, and approaching these diseases with a One Health model.”

Can you develop immunity to malaria?

Not permanent immunity. People can contract malaria many times, partly because there are multiple parasites with complex life cycles. Some people may develop partial immunity with repeated exposures, but this only may help prevent severe disease in some people and not infection, Pastula says.

Is there a malaria vaccine?

Not in the United States. But in other parts of the world, GSK’s RTS,S/AS01, or Mosquirix, was approved by the World Health Organization in 2021 and has been administered to about 1.5 million children, though it’s only about 30% effective in preventing severe disease. BioNTech and the University of Oxford have each also developed experimental vaccines that are in clinical trials.

If I’m traveling to a country where malaria is locally transmitted, are there drugs to help prevent it?

There are several drugs for malaria prophylaxis that your health care provider may recommend. Which one you might take will differ depending on where you’re traveling and what other medications you might be taking. None are 100% effective, so protecting yourself from mosquito bites is still important.

Are there other mosquito-borne diseases we should keep an eye out for?

Dengue, Zika, and chikungunya are examples of diseases endemic to the tropics that have seen occasional outbreaks in the southern continental United States. West Nile virus has been endemic to most of North America since the early 2000s, and we are seeing many cases this season in Colorado.

Can’t we just eradicate Anopheles mosquitoes that spread malaria?

Mosquitoes have been around a lot longer than human beings have, Pastula says. They will likely keep adapting to our efforts to take them out.

“We need to learn to live with mosquitoes – but take them and their bites seriously,” he says.

How does one “live with” mosquitoes?”

Avoid their bites and make life difficult for them. That means using insect repellents and wearing long sleeves and long pants, particularly towards dawn and dusk when mosquitoes are most active. Keep mosquitoes out of your home and, in particular, away from the bedroom, where they can bite at night. If you’re a homeowner, look for standing water and drain it, because it doesn’t take much to provide breeding grounds for mosquitoes.

“If you prevent mosquito bites, you prevent the diseases mosquitoes spread,” Pastula said.

About the author

Todd Neff has written hundreds of stories for University of Colorado Hospital and UCHealth. He covered science and the environment for the Daily Camera in Boulder, Colorado, and has taught narrative nonfiction at the University of Colorado, where he was a Ted Scripps Fellowship recipient in Environmental Journalism. He is author of “A Beard Cut Short,” a biography of a remarkable professor; “The Laser That’s Changing the World,” a history of lidar; and “From Jars to the Stars,” a history of Ball Aerospace.