Dengue Fever, West Nile Prompt Mosquito Concerns in Florida
Friday, September 17, 2010
By: Euna Lhee, Healthy State Collaborative

September 17, 2010 | WMFE - Earlier this month, the West Nile Virus claimed the life of an Orange County resident, making this Florida's first West Nile death this year. In addition, more than a hundred cases of another mosquito-borne illness, dengue fever, have been reported in Florida this year, including seven in Orange County. Mosquitoes carrying the dengue virus haven't been seen in the state for decades, but they have now shown up in Key West and Broward County. With mosquito-borne diseases on the rise, public health officials are increasing mosquito control and surveillance efforts.

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Sporting black pants and steel-toed boots, Sue Durand is certainly not dressed for the weather. Orlando on this Tuesday morning is already 88 degrees – and it’s humid.

But for Durand, dressing up is part of the job.

As a mosquito control specialist for Orange County, Durand goes door-to-door and checks for mosquito breeding in pools of standing water, such as in flower pot saucers and gutters. She collects water specimens loaded with mosquito larvae and then analyzes the wiggling, worm-like samples in the lab to see whether any of them come from a species that transmits diseases, like West Nile Virus and dengue fever.

With mosquito-borne diseases on the rise, public health officials are increasing mosquito control and surveillance efforts. In the meantime, University of Central Florida researchers are studying ways to produce a low-cost vaccine to fight dengue fever, a mosquito-borne illness.

Dengue is also called “break bone fever” because of the excruciating pain it causes in the joints. Many Americans are unfamiliar with the disease, but it’s actually the most common mosquito-borne illness in the world, with 100 million infections occurring every year, mostly in the tropics and subtropics. In the past, most dengue fever cases in Florida were acquired abroad. The state has not seen dengue-infected mosquitoes since the 1930s. But the virus has recently been found in mosquitoes in the southern part of the state, mainly in the Keys, where the Centers for Disease Control estimated over 1000 people were exposed to the virus last year.

“We don’t have the answer to why the outbreak is occurring right now, however, but we did know that it was a possibility,” said Dr. Carina Blackmore, a Florida Department of Health spokesperson.

She said that there are two possible reasons dengue fever has shown up in Florida’s mosquitoes.

“The most likely scenario is that there was somebody who developed dengue in the United States that they had then contracted elsewhere, and then a mosquito in Key West picked up the virus, and the outbreak got started,” Blackmore said. “It is also possible that there was an infected mosquito that came into the United States.”

The type of mosquito that carries the dengue virus is a “lazy” mosquito, in that it does not like to travel very far at all. It usually hangs out around people’s homes and prefers to bite people indoors. The species is fairly uncommon in Central Florida, compared to the southern parts of the state. But it is difficult to control or eliminate when it does make an appearance in the area.

As a result, Orange County sprays residential areas for adult mosquitoes at night. But that may not be enough. The powerful chemicals once used in spraying operations are now banned.

“The strongest pesticides that used to control mosquitoes, quite a few of them like DDT, have been pulled back. Therefore, there’s less effective control of mosquitoes,” said Dr. Henry Daniell, a biomedical researcher at the University of Central Florida.

He said mosquito-borne illnesses, like dengue fever, cannot be eradicated with mosquito control methods alone, until a vaccine is on the market.

“In the case of dengue, there’s no vaccine now. So first, a vaccine has to be developed. It needs to be made affordable and, ultimately, it can be controlled,” Daniell said.

Daniell is working on an oral vaccine derived from plants. The National Institutes of Health is currently testing an injectable vaccine of its own. But Daniell thinks his pills would be cheaper. For one thing, he said they wouldn’t have to be produced in huge, expensive machines, like fermenters.

“They [fermenters] cost anywhere between 700 to 900 million dollars to build. And it’s operated completely in a sterile environment. And then the vaccine is purified and injected. It needs to be cold-chained, protected, refrigerated, and so on,” Daniell said. “Ours eliminate all these costs.”

Daniell acknowledged the need for further research on his oral vaccine and estimated that it will not be available to consumers for at least five years.

Until then, Sue Durand with Orange County Mosquito Control says the only sure way now to prevent dengue fever and other mosquito-borne illnesses is to avoid being bitten by wearing bug spray.

And she had one more important piece of advice.

“Dump any water you have on your property… because that’s where they lay their eggs, and that’s where the mosquitoes breed,” Durand said.