First locally acquired malaria cases diagnosed in 20 years in U.S.

Five cases of malaria have been confirmed in Florida and Texas, the first time the potentially fatal mosquito-borne disease has been locally acquired in the United States in 20 years, the U.S. Centers for Disease Control and Prevention said Monday.

The four Florida cases, along with one in Texas, have been diagnosed over a period of two months, the agency said.

The state of Florida said that its first case was diagnosed on May 26 in Sarasota County, while officials in Texas said on June 23 that a Texas resident who worked outdoors in Cameron County had been diagnosed with the disease.

The CDC said in an alert released Monday that malaria is considered a medical emergency, and that anyone with symptoms should be "urgently evaluated."

However, the CDC said that risk of malaria remains low in the United States, and that most cases are acquired when people travel outside of the country. Fully 95 per cent of malaria infections are acquired in Africa, the health agency said.

Malaria is caused by five species of a parasite carried by certain female mosquitoes. Symptoms include fever, chills, headache, muscle pain and fatigue. Nausea, diarrhea and vomiting may also appear. Malaria can cause life-threatening damage, including kidney failure, seizures and coma.

The state of Florida has issued a mosquito-borne illness alert and recommended that residents drain standing pools of water, make sure their window screens do not have holes in them and use insecticides that contain DEET to repel mosquitoes. Long-sleeved shirts and pants are also recommended when mosquitoes are present.

The state of Texas has also issued a health alert, advising clinicians to routinely obtain a travel history to determine if a patient with symptoms of malaria has spent time outdoors and been bitten by mosquitoes in an area with malaria activity.

Health officials are also warning doctors, especially those in southern states where the weather is more friendly to the tropical mosquito that spreads malaria, to be aware of the possibility of infection. They also should think about how to access the IV drug that is the first-line treatment for severe malaria in the United States, the CDC said.

The agency said that the people who were diagnosed received treatment and "are improving."

About 2,000 U.S. cases of malaria are diagnosed each year — the vast majority in travellers coming from countries where malaria commonly spreads.

Since 1992, there have been 11 outbreaks involving malaria from mosquitoes in the U.S. The last one occurred in 2003 in Palm Beach County, Fla., where eight cases were reported.