that they must have caught near where they live—because, according to health officials, none of them traveled outside the US or their own states. The very unusual discovery has left infectious disease specialists wondering: Who else might be ill, and will local doctors recognize what’s wrong?
Malaria isn’t completely unprecedented in the US: About 2,000 residents contract it every year, but almost always because they traveled to a place where it’s endemic, were bitten by an infected mosquito there, and fell ill once they came home. Locally acquired malaria is extremely rare. It arises from a chain of transmission that probably starts with a US mosquito biting a tourist, migrant, or refugee who has been in an endemic country and is carrying the infection in their blood.
There are roughly 247 million cases of malaria in the world each year, according to the World Health Organization, and in every one a mosquito is only the vector. Humans are the disease’s natural host; mosquitos transport it between people.
“If there are five cases right now, that means there's got to be a lot more mosquitoes out there that are infected,” says Ross Boyce, a physician and assistant professor at the University of North Carolina at Chapel Hill School of Medicine, who runs a malaria research program in Uganda. “And there may even be more people that are infected than we know about at this point.”
The five people identified by health authorities, in Sarasota County on Florida’s west coast and Cameron County at the southernmost tip of Texas, have already received treatment and are recovering, according to the Centers for Disease Control and Prevention. In both areas, mosquitoes have been trapped and analyzed, and mosquito-control districts are spraying insecticide to knock down local populations.