Dengue virus returns to Florida after more than 50 years, UF researchers say

GAINESVILLE, Fla. — University of Florida mosquito researchers are watching with a wary eye as dengue virus returns to the state after more than 50 years.

By late last week, 20 cases of locally transmitted dengue had been confirmed in Key West. Monroe County officials have issued a health alert and launched an education campaign urging residents to eliminate water sources in and around their homes where mosquitoes can breed.

“We haven’t seen dengue in Florida in a long time, but this does give us evidence that we can have it again,” said Roxanne Connelly, an associate professor of medical entomology with UF’s Institute of Food and Agricultural Sciences.

Dengue fever, also known as break-bone fever or bonecrusher disease, is a rarely fatal but widespread disease transmitted to humans via the bite of an infected mosquito. There are an estimated 100 million cases of dengue worldwide each year.

As its names suggest, dengue brings high fever, severe headaches and joint and muscle pain. It is often misdiagnosed as influenza.

Besides the dengue re-emergence in the Florida Keys, Connelly, based at the Florida Medical Entomology Laboratory in Vero Beach, said health officials were surprised by a door-to-door survey of Key West residents. Connelly and Jonathan Day, a medical entomology professor at the Vero Beach laboratory, collaborate with the health and vector-control officials.

After some 240 residents allowed health officials to draw a small blood sample, test results showed that 41 percent had been exposed to the dengue virus or other Flavivirus, either through exposure to one of the viruses or through vaccinations, such as the yellow fever vaccine.

“Much like a lot of other mosquito-borne diseases, some people can have it and not have any symptoms, while others end up very sick,” Connelly said.

The last big dengue epidemic in Florida was in 1934 and left more than 25,000 Floridians ill, Day said.

Researchers don’t expect this outbreak to reach beyond Monroe County, but it’s a strong reminder for Floridians to be on guard.

Dengue is spread by two mosquito species, commonly known as the yellow fever mosquito and Asian tiger mosquito. Both lay eggs on the sides of water-filled containers.

The yellow fever mosquito is mostly confined to South Florida, while the Asian tiger mosquito is found throughout the state, though not in the Florida Keys.

The yellow fever mosquito is prevalent in the Old Town part of Key West, Day said, and has an affinity for a local cemetery full of rain-catching urns and vases. Many of the recent dengue cases were in the Old Town area, he said.

Unlike many mosquitoes that are active in the morning and evening, the yellow fever and Asian tiger mosquitoes are unusual in that they will bite in broad daylight.

Connelly advises residents to take a careful look at their homes and yards, looking for even tiny amounts of standing water. Boat tarps, birdbaths, gutters, empty soda cans ─ anything that will hold water should be suspect and emptied or discarded.

Pet dishes emptied every few days aren’t a worry, she said. And while it’s not as common, residents can inadvertently breed mosquitoes indoors, she said.

One way: Small decorative bamboo plants hold just enough water to interest a mosquito looking to lay eggs.

Other suggestions for residents include wearing long pants and sleeves when possible and wearing a repellent that includes the active ingredient DEET.

Connelly and Day are members of UF’s Emerging Pathogens Institute, whose researchers work to prevent or contain new and re-emerging diseases that threaten Floridians.


Writer: Mickie Anderson, 352-273-3566,

Sources: Roxanne Connelly, 772-778-7200, ext. 172,

Jonathan Day, 772-778-7200, ext. 132,


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Posted: November 23, 2009

Category: Pests & Disease, UF/IFAS Research
Tags: Connelly, Day, Dengue, Entomology And Nematology, Key West, Mosquito

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