Infected mosquitoes spread dengue to people. Symptoms include high fever, headache and body pain, which is how it got the nickname "breakbone fever."
People typically contract it while traveling through a continent where the virus is always present, like South America, Asia or Africa.
But this year, folks who got infected during their worldly adventures brought it back to the U.S., passing it on to the mosquitoes here.
Now, nearly 500 cases that are not travel-related have been reported in Florida.
"I have not seen anything like this. … It is very much unprecedented," said Eva Buckner, an insect scientist at the University of Florida.
The largest outbreak of locally acquired dengue in the continental U.S. in nearly a century is happening in Florida, with Hillsborough County at the epicenter. The mosquito-borne virus even caused the death of an 80-year-old Tampa woman in September.
The spread was triggered by multiple factors.
Why Florida and Hillsborough?
Bucker said dengue has been recently very active globally.
"Which allows multiple travel cases to occur in Florida,” she said.
Plus, the state already has the type of mosquito that can carry dengue: Aedes aegypti. And then there was a long drought this year.
"Aedes aegypti has drought-resistant eggs, and so it allowed some of the eggs to build up in the environment,” Buckner said.
So, when it finally rained in June, all those eggs hatched simultaneously — just in time for a hot, humid summer, in which these mosquitoes thrive.
Cases spiked in the Tampa area because officials weren't prepared to fight this tropical disease like they already do in more southern Florida counties like Miami-Dade or Lee.
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"It's not something we deal with from a local transmission standpoint often, but we have tons of infrastructure and tons of areas that definitely lend itself to it,” said Gabriela Henderson with Hillsborough's Mosquito Management.
A main hotspot, she said, continues to be the populated area north of Ybor City because of the many businesses, and people walking to and from work or going to lunch. And then there are those unable to seek shelter, like unhoused folks.
"If this was going to happen anywhere in an unexpected way, it's definitely Tampa,” Henderson said.
The Florida Department of Health is doing an in-depth history, investigating how the outbreak started.
Warming temps and dengue
Zooming out of Hillsborough, Florida and even the U.S., infectious disease researchers are documenting a global trend linking warming temperatures and the spread of dengue.
Erin Mordecai with Stanford University co-authored a study published last year that found climate change increases the chance of temperatures reaching 84 degrees in more places, which is optimal for dengue transmissions.
"We estimate that about 18% of the global dengue burden is attributable to climate change that had already happened by 1995 to 2014 – so not even including the last decade of warming,” Mordecai said.
This analysis was done in 21 countries in Latin America and Asia, using documented cases of dengue and recorded temperature data sets from each country.
After comparing each place to itself over time, researchers found that as the temperature rose so did dengue cases.
"We project a pretty large further increase in dengue transmission by mid-century,” Mordecai said.
A rise of 76% by 2050 under a worst-case scenario, if the level of polluting emissions that cause climate change don’t drop. Best-case scenario is still 49%.
Mordecai said researchers are currently studying the U.S. on what conditions allow for locally acquired dengue transmissions in places where it’s not endemic.
For now, weekly cases of dengue are slowing a bit, while still persistent, in Florida as the state welcomes cooler, drier air.
You can protect yourself from dengue by applying mosquito repellent and removing debris around your home that may pool water where Aedes mosquitoes breed.
