University of Nebraska Medical Center

What could cause a malaria comeback in the US — and what could stop it

Vox Americans shouldn’t take a malaria-free future for granted.

Over the last month, five people in the US (four in Florida and one in Texas) have acquired malaria within the country’s borders. That’s pretty uncommon — at least, in this century; until the 1950s, malaria was a persistent plague in the US, especially in the Southeast.

Many of the conditions that favor malaria’s spread haven’t changed much since then. The Anopheles mosquitoes that spread malaria still thrive in many parts of the country, and states that receive high numbers of travelers from countries where malaria is endemic still have warm, wet weather that favors mosquito reproduction.

Nevertheless, it’s extraordinarily rare for American mosquitoes to be infected with malaria. Since the turn of the last century, there have been only about a dozen cases of local malaria transmission in the US. But the disease remains a major force of destruction elsewhere in the world: In 85 countries across Africa and parts of Asia and South America, malaria caused 240 million illnesses and 627,000 deaths in 2020 alone.

The last spate of local malaria transmission in the US took place 20 years ago. Now circumstances are different: These cases are happening amid rising rates of other insect-borne infections nationwide, and smack in the middle of a heat and wildfire wave that together make climate change’s health risks undeniable. It’s reasonable to wonder whether the US is at risk for becoming a malaria hot spot again.

“Something would have to go seriously wrong for malaria to become endemic in the United States,” said Colin Carlson, a global change biologist at Georgetown University’s Center for Global Health Science and Security who has led research on the rapidly expanding reach of malaria-spreading mosquitoes in Africa.

It’s perhaps the understatement of the year to say the nation is not immune to “things going seriously wrong.” Recent history, ahem, has shown that the country’s public health infrastructure, which Americans rely on to catch and contain invasive infectious diseases, is far more fragile than many realized.

But how vulnerable is the nation, really, to a malaria comeback?

Here’s what the US has going for it — and against it — when it comes to future malaria risk.

The US has some things in its favor in the fight against a malaria resurgence

One key factor the US has going for it is that it’s already eliminated malaria. “Our centralized focus” on getting rid of both malaria parasites and their mosquito hosts’ breeding grounds “really kicked it in the butt,” said Kyndall Dye-Baumuller, a post-doctoral student in vector-borne disease epidemiology at the University of South Carolina’s public health school.

Containing a handful of malaria cases — and eliminating a handful of malaria-infected mosquitoes — is much easier than battling back an infection that’s already entrenched.

That’s also made easier by the fact that most malaria only causes disease in humans and not in any other animal, said Dye-Baumuller. She compared the infection with West Nile virus, another infection spread by mosquitoes that leads to illness in humans and in a variety of wild birds. Because it’s so hard to contain this virus in the bird population, there’s a persistent reservoir of West Nile virus in many parts of the US — and the persistent risk of some crossover to humans. That’s not a risk with malaria.

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