Malaria has a rich history in the US. Should Americans be worried about rising cases?

Most Americans don't worry about malaria. The disease has largely been a thing of the past in the United States for two decades.

That's why reports of several new cases of the mosquito-borne illness in two separate outbreaks in Florida and Texas has garnered recent headlines. This week, the Gulf Coast county of Sarasota, Florida, reported another unusual, locally transmitted case of the disease.

While malaria drugs and current vaccines are becoming less effective over time, experts say the disease is unlikely to make a comeback in the U.S. The nation's public health agency, the Centers for Disease Control and Prevention, was founded in the fight against against the illness in Southern states, and the surveillance system it set in place continues to be an effective defense, they say.

But more travel and hotter temperatures could make malaria hotspots more frequent, experts say.

“We shouldn’t be surprised that we’re going to have sporadic outbreaks again,” said Dr. Thom Eisele, professor and director of the Center for Applied Malaria Research and Evaluation at Tulane University School of Public Health and Tropic Medicine. “The ingredients are here for transmission to happen, but we have a lot of safeguards.”

Malaria in the US

Malaria is one of humanity's oldest diseases, and it's no stranger to the United States.

The mosquito-borne disease was one of the country’s leading causes of death in the 19th century, causing more than 45 out of every 1,000 deaths in 1850, according to Census Bureau data. Malaria devastated troops during the Civil War, causing more than a million cases and 10,000 deaths, and wreaked havoc in the South where the parasite was common.

Malaria is a serious and sometimes life-threatening disease caused by the bite of an infected female mosquito from the genus Anopheles, causing symptoms like chills, fever, headache, nausea, body aches and diarrhea. These symptoms typically occur seven to 30 days after people are infected with the parasite.

However, if the infection is untreated, more severe symptoms may appear, including mental confusion, difficulty breathing, convulsions, abnormal bleeding and more, which can lead to death.

In 1942, the U.S. established the Office of Malaria Control in War Areas (MCWA) in Atlanta to limit the spread of malaria by focusing on public health measures that controlled mosquitoes transmitting the disease.

State and local health agencies from 13 Southern states began using the insecticide DDT in counties where malaria was reported, spraying millions of homes and using aircrafts for large areas. They also drained wet areas where mosquitos thrive and breed.

By 1949, malaria was declared to be no longer a significant public health threat, and the MCWA transitioned into a surveillance role, becoming today's CDC.

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The public health campaign was successful in eliminating transmission within the country, but sporadic cases brought in by infected travelers from other countries still occurred. Before the COVID-19 pandemic, about 2,000 cases of travel-related malaria were diagnosed in the country each year, according to the CDC.

“Elimination in the United States means there’s no longer ongoing local transmission for a certain time,” said Dr. Shauna Gunaratne, an expert in tropical medicine and assistant professor of clinical medicine at Columbia University Irving Medical Center. “In the cases that we’ve subsequently seen, the vast majority are imported cases where they’re acquired overseas and diagnosed in the United States.”

Domestic transmission can still occur, however, if a mosquito in the U.S. bites a person infected elsewhere and transmits the parasite. Experts say this is what likely happened recently in the U.S., and the disease spread locally.

Do mosquitoes in the US carry malaria?

Most mosquitoes don’t carry the parasite that causes malaria – only an infected female mosquito from the genus Anopheles can transmit the disease.

These mosquitoes can be found throughout the United States. They typically prefer to feed on people or animals late in the evening or at night, according to the CDC.

They’re attracted to dark and sheltered areas and typically feed there, Eisele said. That feeding preferences makes it harder for female Anopheles mosquitoes to transmit malaria in the United States, but the species of parasite found in Florida and Texas can lay dormant in a person's liver for weeks, months, or even years.

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This species of parasite, called Plasmodium vivax, also causes less severe symptoms compared to other common varieties, which means people may be less likely to go to the hospital and receive treatment, said David Fidock, professor of microbiology, immunology and medical sciences at Columbia University Irving Medical Center.

“People could be walking around with infections in their liver without knowing,” he said. “There could be many more undiagnosed individuals who have fever and chills and think they have some bacterial or viral infection and don’t realize it’s malaria."

The CDC recommends using "mosquito avoidance measures" when going outside, including:

• Using EPA-approved mosquito repellent on skin and clothes.

• Wearing long-sleeved shirts and pants, especially at night.

• Staying in well-screened areas.

• Sleeping under an insecticide-treated bed net when camping.

When traveling out of the country, people should consult their doctor about vaccines and medicines that can be taken to prevent diseases.

Is there a malaria vaccine? Is malaria easily curable?

Malaria is treatable and certain medications can be taken to prevent infection before traveling to a country where the disease is prevalent.

But like other pathogens, the CDC says certain strains are becoming resistant to the first line of defense drugs – chloroquine – and other common antimalarial drugs.

“There are effective medicines, but there’s also a big issue in the world with regards to the drug resistant forms of malaria,” Fidock said. Certain parasites have "acquired resistance to nearly all malaria drugs.”

Researchers have spent decades developing vaccines for malaria, however, only recently has one been approved.

The RTS,S/AS01 vaccine by GSK, formerly known as GlaxoKlineSmith, is the first vaccine to help protect children against malaria. Formally recommended by the World Health Organization in 2021, the vaccine is typically used in areas of the world where malaria is more common.

But the vaccine is not ideal as it offer less than 40% of protection and requires three doses, said Nirbhay Kumar, professor of global health at George Washington University Milken Institute School of Public Health.

Other malaria vaccines are in the works, but the parasite is notorious for evading immunity.

“They have a very complex life cycle and because of this it’s been very difficult to nail down the parasite by developing effective vaccines,” Kumar said.

What should Americans expect in the future

The handful of cases in Florida and Texas aren’t cause for widespread concern, experts say. But local cases of malaria are likely to stick around.

Cases are likely to become more frequent as travel increases and climate change makes certain areas of the country more hospitable to mosquitoes carrying the disease, Gunaratne said.

“I do not think malaria is going to gain a foothold,” she said. “However, we are anticipating a lot of travel this upcoming summer, and the CDC is advising people and health care providers to be vigilant about the possibility of more imported malaria cases.”

Experts say the recent cases have put a needed spotlight on malaria, as more than 600,000 people worldwide continue to die each year from the disease, according to the World Health Organization.

The U.S. can’t be rid malaria if it’s still thriving in other parts of the world, Eisele said.

“The front line of malaria is in Sub-Saharan Africa and other endemic countries … that’s where our investments need to be put,” he said. “It’s about combating malaria where it is locally and having good surveillance systems in the U.S.”

Contributing: Carlie Procell and Janet Loehrke, USA TODAY. Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT.

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.

This article originally appeared on USA TODAY: Malaria in the US: Should Americans be worried about rising cases?