The US states of Florida and Texas have diagnosed the first malaria cases in decades, raising fears of another outbreak.
The Centers for Disease Control (CDC) and Prevention said on Monday that five cases of malaria have been confirmed in the two states.
This is the first time in 20 years the potentially fatal mosquito-borne disease has been locally acquired in the United States.
The four Florida cases, along with one in Texas, have been diagnosed over a period of two months, the CDC 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.
In an alert issued on Monday, the CDC warned that malaria is a medical emergency that requires urgent evaluation for anyone with symptoms.
It said, however, that malaria risk is still low in the US, and most cases are from people who travel abroad. The health agency noted that Africa is where most malaria infections occur, accounting for 95 percent of cases.
Malaria is a disease caused by a parasite that some female mosquitoes carry. It can cause fever, chills, headache, muscle pain and fatigue, as well as nausea, diarrhea and vomiting. Malaria can also lead to life-threatening complications, such as kidney failure, seizures and coma.