The Centers for Disease Control and Pfrevention (CDC) said in an alert released Monday that malaria is considered a medical emergency, and that anyone with symptoms should be "urgently evaluated."
The four Florida cases, along with one in Texas, have been diagnosed over a period of two months, the U.S. health 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 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.
Despite the emergence of malaria cases, 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% 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.