Florida's Dengue Outbreak Is the Largest in Decades, and Texas Shares the Mosquito

Florida health officials reported this week that more than 250 locally acquired dengue cases have been tallied in the state so far this year, the vast majority of them in Hillsborough County around Tampa. The Associated Press, reporting the figure on Oct. 5, described it as the largest outbreak of the mosquito-borne disease in the continental United States in several decades — larger than Florida's previous worst year, 2023, which came in just under 200 locally spread cases.

Hillsborough and neighboring counties have declared local emergencies, and crews in the Tampa area are spraying around the clock. One death has been recorded, an elderly Tampa woman on Sept. 4.

Dengue is caused by any of four closely related viruses, which is the detail that makes it difficult to manage. A first infection builds lifetime antibodies against that one serotype, but those antibodies can fail against a second serotype and, in some cases, help the virus enter immune cells and replicate. That antibody-dependent pattern is why second infections are the dangerous ones and why an effective vaccine has been so hard to build. CDC notes the U.S. vaccine is recommended only for children 9 through 16 with laboratory-confirmed prior infection who live where dengue is common. There is no specific treatment beyond fluids, rest and acetaminophen.

The global numbers dwarf the Florida outbreak. The World Health Organization has logged more than 2.2 million infections and nearly 1,200 deaths this year, and CDC counts close to 1,900 locally acquired U.S. cases, most of them in Puerto Rico. What makes Tampa stand out is where the cases came from: as of last week, locally acquired Florida infections had edged past travel-associated ones, 252 to 245.

Texas is not on the bleachers. CDC lists five states where limited local dengue transmission has been reported — Florida, Hawaii, Texas, Arizona and California. The AP dispatch notes that the 2009–2010 Key West outbreak was the first locally acquired dengue in the continental U.S. outside the Texas-Mexico border since 1945, a reminder that the border region has its own history with the virus. The mosquitoes that carry it, Aedes aegypti and Aedes albopictus, are established along the Texas Gulf Coast and in most of the state's urban cores.

Why Tampa, this year, is not fully settled. Dawn Wesson, a Tulane University researcher who studies dengue and other mosquito-borne diseases, told the AP that Florida's case load tracks travel — the state receives a steady stream of people arriving from Puerto Rico and other places where the virus circulates — and that the shift north of the usual Miami-area pattern may owe something to travel patterns as much as to weather. Most people in the Tampa area, she said, have no prior immunity to any form of dengue.

Federal involvement has been limited. A CDC spokesman said the agency has provided $800,000 in assistance to Florida's health department but has not sent disease investigators, because the state has not asked for them.

The prevention advice for Texas homes and businesses is the one that vector control has repeated since the West Nile seasons began, with one adjustment that matters here: Aedes aegypti bites during the day. Dusk-and-dawn caution does not cover it. Standing water in tires, planters, pet bowls, clogged gutters and tarps should be dumped weekly, screens and door sweeps repaired, and repellent with DEET, picaridin or IR3535 used on exposed skin. Pest control operators working Gulf Coast properties have a role that extends past fogging: source reduction, larvicide in the drains and catch basins that hold water, and barrier treatments around shaded resting sites.

Anyone who returns from Florida or the Caribbean with a fever should mention the travel to a clinician, since dengue symptoms typically begin within two weeks of an infected bite. For Texas, the broader lesson is unchanged. The mosquito is already here; what moves the numbers is what people do with the water it needs.