Dengue fever researcher talks Florida outbreak — and transmission risk
Authorities in Florida have declared local states of emergency following an outbreak of dengue fever, a mosquito-borne viral disease that is uncommon in the U.S. but causes sporadic outbreaks in Florida.
Authorities in Florida have declared local states of emergency following an outbreak of dengue fever, a mosquito-borne viral disease that is uncommon in the U.S. but causes sporadic outbreaks in Florida.
This month, the state recorded a rare death from the disease, which the Florida Department of Health confirmed in an email to Northeastern Global News on Friday. Its most recent data shows that there were 38 new locally acquired dengue cases between Sept. 13-19, bringing the 2026 total to 190 cases across six counties. That is on top of the 212 travel-associated cases. The virus has also been detected in 17 mosquito pools this year.
Michael Johansson, a Northeastern University researcher who has studied dengue for two decades, told Northeastern Global News that the number of locally acquired cases in Florida so far this year is “clearly elevated,” particularly in the Tampa Bay area, compared to the past decade.
“The number of travel-associated cases are more in the normal range,” said Johansson, a research professor of public health and health sciences.
What is dengue fever?
Dengue is caused by four related virus types, or different strains of the same virus: dengue virus 1, 2, 3 and 4, according to the Centers for Disease Control and Prevention, or CDC. Symptoms can range from mild to severe and commonly include fever, aches and pains, nausea, vomiting and rash, while some cases can develop into severe dengue.
Symptoms usually begin within two weeks of a bite from an infected mosquito and typically last two to seven days, with most people recovering after about a week, according to the CDC.
Johansson said Florida is home to both Aedes aegypti and Aedes albopictus, the two mosquito species capable of transmitting dengue. Aedes aegypti is the more common dengue vector, he said, adding that species is most commonly associated with the local chains in the ongoing Florida outbreak.
“Not all mosquitos carry dengue, but we know the right ones are there. All the ingredients are there,” Johansson said.
How is it transmitted?
Dengue fever is transmitted when a mosquito bites a person who has the virus in their blood, picking up the virus in the process and then passing it to someone else in the same fashion. It takes about a week for a mosquito to become a carrier, though the timing depends on the temperature. In general, the warmer the environment, the quicker the virus develops inside the mosquito, Johansson said.
An “imported case” refers to someone who contracted the disease elsewhere, typically while traveling abroad, and then introduces the virus to local mosquitoes when they arrive at another location and are bitten.
This could lead to more mosquitos carrying the disease — and, thus, a few more infections than there would be otherwise, Johansson said.
Johansson and his colleagues have analyzed data from Miami-Dade, where dengue transmission has been more common, and found that local spread is more likely to occur in smaller, isolated chains. He said that it is still unclear whether the rising caseload reflects one sustained chain of transmission or “multiple smaller introductions.”
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Global prevalence of dengue fever
Dengue is most common in tropical and subtropical regions, including much of Latin America and the Caribbean, Southeast Asia and the Pacific Islands, as well as parts of Africa and the Middle East, according to the CDC. The virus is most common in regions where the Aedes mosquitoes that transmit it can survive, particularly warm climates where the mosquitoes often live in and around human communities.
Dengue has expanded considerably around the world over the past several decades, according to health experts. Cases reported worldwide climbed from roughly 500,000 in 2000 to 14.6 million in 2024, though the true burden is likely much higher because many infections cause few or no symptoms and never enter official counts, according to the World Health Organization. The disease is now established as endemic in more than 100 countries, meaning that it is constantly present.
“The general trends show there are more dengue cases, malaria, yellow fever and West Nile Virus reported in the U.S. over the past decade,” Richard Wamai, a Northeastern professor and an expert in neglected tropical diseases, said in an email. “And this also is the general trend globally, especially for the deadly malaria.”
Wamai said the spread of dengue is exacerbated by climate change, regional gaps in disease surveillance and health education, among other factors. Warming temperatures and changing rainfall patterns, along with migration and travel, can create more favorable conditions for dengue-carrying mosquitoes to proliferate, he said.
What can be done to stop the spread?
Florida Surgeon General Joseph Ladapo urged residents to take protective measures, including using insect repellent, covering up when possible and removing standing water around homes.
Though severe outcomes are rare, education and awareness on the part of physicians and health care providers is important because dengue is occasionally fatal, Johansson said.
“Recognizing the disease and providing supportive treatment can greatly improve a patient’s chances of survival,” he said.
