The Centers for Disease Control and Prevention on Monday warned of the return of locally acquired cases of malaria, meaning the infections were not linked to foreign travel and appear to have been transmitted by mosquitoes in the U.S. carrying the parasite.

So far, there have been four locally acquired cases of malaria in Florida and one in Texas within the last two months. There's no evidence suggesting the cases in the two states are connected.

"Malaria is a medical emergency and should be treated accordingly," the CDC wrote in a Health Alert Network Health Advisory. "Patients suspected of having malaria should be urgently evaluated in a facility that is able to provide rapid diagnosis and treatment, within 24 hours of presentation."

Each year, around 2,000 cases of malaria are diagnosed in the U.S., but they're usually connected to people who've traveled out of the country. 

"Despite certification of malaria eradication" in the U.S. in 1970, "small outbreaks of locally acquired mosquito-transmitted malaria continue to occur," the CDC wrote in 2003.

Locally acquired mosquito-borne malaria has not occurred in the U.S. since 2003, when there were eight cases identified in Palm Beach County, Florida. 

The new cases in Florida were identified in Sarasota County, the state's Department of Health said. Officials in the state issued a statewide mosquito-borne illness advisory on Monday. All four individuals who caught the illness in the state have been treated and have recovered.

A health advisory has also been issued in Texas. 

Malaria, which is caused by a parasite that commonly infects a certain type of mosquito, can be fatal. The World Health Organization estimates the disease killed 619,000 people worldwide in 2021. But the illness can be treated and cured with prescription medications.

Symptoms include high fevers, shaking chills and flu-like illness. Nausea, vomiting, and diarrhea may also occur. While most people show symptoms that start 10 days to 4 weeks after infection, a person may feel ill as late as one year after infection.

The disease is not contagious between humans; people can get malaria by being bitten by an infective female Anopheles mosquito. 

The CDC advises the public to take steps to prevent mosquito bites and control mosquitoes at home. To prevent bites, use insect repellent. The health agency also advises wearing loose-fitting, long-sleeved shirts and pants. At home, use screens on windows and doors and use air conditioning if it's available.

In:
• Texas
• Florida

Aliza Chasan

Aliza Chasan is a digital producer at 60 Minutes and CBS News.

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