The CDC says that if you have a mystery fever this summer, there's a chance it could be malaria

• Malaria is circulating again in the US this summer. Five local cases have been diagnosed in Florida and Texas.
• It's easy to prevent and treat, but isn't typically on the radar of doctors in the US.

Malaria is circulating again in the US. The Centers for Disease Control and Prevention said five cases of locally acquired malaria have been detected so far this summer — four in Florida, and one in Texas.

The cases are striking as malaria was declared eradicated from US shores in 1951 — though rare cases have been seen locally in the years since, most recently in 2003, when a cluster of eight people caught malaria in Palm Beach, Florida.

Typically, the approximately 2,000 people who are diagnosed with malaria in the US each year have recently traveled to a place in the world where the disease regularly circulates.

But something unusual must have happened this summer — travelers who came back from places in the world where malaria is more common got the disease, and were then bitten by mosquitoes in Texas and Florida. Then, those same mosquitoes, carrying malaria parasites, flew away and bit other people, causing local transmission.

"There's a lot more people who are traveling now, post-COVID, and going to areas where malaria is endemic," Dr. Jill Weatherhead, a tropical medicine expert at Baylor College of Medicine, told Insider.

The cases are unusual and numerous enough that the CDC sent out an emergency health alert earlier this week to notify doctors of the uptick. The CDC is asking doctors to "consider a malaria diagnosis in any person with a fever of unknown origin regardless of their travel history."

Malaria can be deadly, but symptoms may start out like the flu

Symptoms of malaria are often "nonspecific" Weatherhead said, and can look a lot like the flu.

"Fever, myalgias (muscle aches), headaches, fatigue," are some of the most common symptoms, she said. "Healthcare providers may not think of it as a potential diagnosis in a person who hasn't traveled."

The good news is that malaria is very quickly and effectively treated with prescription drugs. The type of malaria being diagnosed in the US, caused by Plasmodium vivax, is not one of the more deadly forms of the disease. Another malaria parasite, Plasmodium falciparum, which is typically found in sub-Saharan Africa, is the most dangerous of the five species.

But there is still a risk that the vivax parasite can lie dormant in the liver and relapse in months or years, which is why Weatherhead recommends patients take a "secondary medication" to nix any dormant parasites.

How to prevent malaria

Weatherhead said there are a few key prevention measures everyone can practice to avoid catching malaria, both in the US and abroad:

• Try not to get bit by mosquitoes, especially around dusk and at nighttime when the anopheles mosquitoes, which transmit malaria, are most active. Wear long sleeves or long pants, and use bug spray.
• Get rid of standing water outside your home where mosquitoes can breed. Keep trash lids closed, empty dog dishes and other open containers of water outside at night, and generally make sure you aren't providing extra opportunities for mosquito breeding grounds to thrive.
• Take antimalarial medicine if you're traveling to an area of the world where malaria is endemic. Drugs like Malarone and doxycycline can be prescribed at travel clinics.

Malaria researcher Jim Kublin, a global health and vaccine research expert at Fred Hutch, said he hopes this is an opportunity to "raise awareness to the significant burden of malaria that exists worldwide."

Malaria kills hundreds of thousands of people, mostly children, every year. And anywhere that is hot and tropical year-round, like Florida, there is an increased possibility for malaria transmission to occur.

"In the US, I think control is relatively easy compared to countries where it's highly endemic," Kubin said. "If you detect early and treat quickly, people will not be transmitting to the mosquito that will then transmit to other people."