The Centers for Disease Control and Prevention issued a health alert to physicians, public health authorities and members of the public on Monday after documenting five cases of malaria acquired within the US in the past two months.

The cases, four in Florida and one in Texas, are the first in 20 years to be locally acquired, meaning the infections were not related to travel outside the country. The last local cases of this type were identified in 2003 in Palm Beach County, Florida.

There is no evidence to suggest that this year’s Florida and Texas cases are linked, the CDC said, adding that the risk across the country remains extremely low.

Malaria is a serious, sometimes fatal disease that is usually transmitted by mosquitoes. The disease is not transmitted from person to person, but mothers can transmit malaria to their fetuses during pregnancy or to their babies during delivery.

«Malaria is a medical emergency,» the CDC alert said.

All five patients have received treatment and are recovering, according to the agency.

The Texas Department of State Health Services announced last week the detection of a local case of malaria in a person who had spent time working outdoors. The person had not traveled outside of the country or state.

The department advised Texans to protect themselves from mosquito bites by using insect repellent and wearing long sleeves and pants. Since mosquitoes lay eggs in standing water, the department also encouraged people to drain puddles, keep gutters clear, cover trash bins and regularly change water in pet dishes and birdbaths.

Meanwhile, the Florida Department of Health issued a State Notice on Mosquito-Borne Diseases on Monday, which said all four of its cases were reported in Sarasota County.

The recent cases in the US were caused by a parasite that infects mosquitoes called P. vivax, according to the CDC. The parasite is not as deadly as other malaria-causing parasites, but it can lie dormant in the body and cause chronic infections months or years after an initial illness.

Typical signs of malaria include fever, chills, headache, muscle aches, and fatigue. Some patients may also experience nausea, vomiting and diarrhea, according to the CDC. Symptoms usually appear 10 days to four weeks after being bitten by a mosquito.

In its health alert, the CDC said malaria cases may also begin to rise this summer due to increased travel to and from places outside the US.

Before the covid pandemic, the US had about 2,000 cases of malaria each year, almost all detected in people who had traveled to other countries. About 5 to 10 people die annually, the CDC said.

The CDC said doctors and hospitals should have a plan to quickly diagnose a malaria patient so they can start giving antimalarial drugs within 24 hours. In particular, the agency said, hospitals should have ready an intravenous version of a drug called artesunate, the only one approved to treat severe malaria in the US.

The CDC also advised anyone planning to travel to an area where malaria is transmitted to talk to their doctors about taking preventive medicines.