An individual in Florida has been infected with a deadly mosquito-borne virus despite not leaving the state, health officials have said.
The patient was in Hillsborough County, which includes the Tampa area, and was diagnosed with dengue fever, a disease that is often asymptomatic but, in some cases, can cause life-threatening internal bleeding and a deep pain in bones that patients say feels like they are being broken.
The individual had not recently traveled outside the US, marking the first case this year of dengue spreading inside America’s borders.
It came as the CDC updated its travel alert for the virus after detecting unusual upticks in cases across the world.
In particular, the agency warned travelers heading to 11 countries and territories to take precautions, highlighting a rise in cases in these areas.
The CDC said it had identified a ‘higher-than-expected number of dengue cases among US travelers returning from’ Bolivia, Cambodia, Colombia, Kenya, Malaysia, Maldives, New Caledonia, Samoa, Sri Lanka, Tonga and Vietnam.
Health officials urged travelers to wear insect repellent, long-sleeved shirts and long pants when outdoors, and to sleep in air-conditioned rooms or a room with window screens.
They warned that children under five, adults over 65 and pregnant women were considered to be at higher risk from the virus.
Pictured above is an Aedes aegypti mosquito, the species which carries the dengue fever virus
Dengue fever was nearly eradicated in the US in the 1970s amid a campaign to wipe out the Aedes aegypti mosquito, identified by the white bands on its legs, which carries the virus.
After that campaign was abandoned, however, the mosquito – and dengue fever – have repeatedly triggered sporadic outbreaks, particularly in Florida and California.
Most cases of dengue fever recorded in the US are linked to international travel.
Hillsborough County, where the first case of locally-transmitted dengue this year was recorded, is the fourth most populous in Florida and has some 1.5 million residents.
It was not clear how the virus entered the country, but experts say this can happen if mosquitoes stow away on ships.
It may also happen if an infected traveler returns to the US and is bitten by an Aedes mosquito, which then becomes infected and transmits the virus to another person when it also bites them.
In 2025, Florida recorded 71 cases of dengue fever that were locally acquired in the state, while seven were also recorded in California and two in Arizona.
Since 2010, there have been 600 cases of dengue fever that were diagnosed in people who had not recently left the country.
Shown above is Tampa, Florida, within the county where the case was detected
The CDC updated its level 1 travel alert for dengue fever, which urges people to practice precautions because of the presence of an outbreak.
In the alert, the agency said: ‘The sharp increase in travel-associated dengue highlights an urgent need for enhanced prevention strategies, improved clinical awareness, and tailored messaging for travelers to areas with ongoing dengue transmission.’
Dengue fever, spread by mosquito bites, often causes an asymptomatic infection, but in some patients it can trigger life-threatening internal bleeding, respiratory distress and heart failure.
It can also lead to shock and organ failure, especially of the liver, brain and heart.
Health officials say about 40 to 80 percent of people infected with dengue fever do not develop any symptoms. If symptoms do develop, they appear abruptly about five to seven days after infection.
Warning signs include a fever above 100F (38C), severe headache, pain behind the eyes, bone, joint or muscle pain, and bleeding in the gums.
Some patients also develop a rash several days after experiencing a high fever.
There is no specific cure for dengue fever and treatment consists of supportive care and therapies to manage symptoms and complications.
Doctors recommend patients with mild symptoms drink plenty of fluids and take Tylenol to ease pain.
In severe cases, patients may be admitted to the hospital for supportive care, an IV, blood pressure monitoring and a transfusion to replace lost blood.
To protect against dengue fever, there is a three-dose vaccine available, which is recommended for children aged nine to 16 years. It slashes the risk of a symptomatic infection by about 80 percent.
