Scientists Wonder Why Florida's West Nile Cases Are Relatively Low
The Associated PressST. PETERSBURG, Fla. (AP) - Despite Florida's reputation as a mosquito's paradise, scientists are trying to explain why its number of human West Nile virus cases have been low compared to other states.
Although Florida has a wet, hot climate that helps spawn and spread its 68 species of mosquitoes, a human epidemic of the illness just hasn't taken hold.
"Isn't that amazing?" said Julia Gill, epidemiology program manager for the Pinellas County Health Department. "We as scientists have a lot to learn about how this disease is going."
More than 6,600 U.S. residents have gotten the disease this year, and about 140 have died. Colorado leads the nation with more than 2,100 cases. Nebraska has more than 1,100 cases and South Dakota close to 900.
This year, Florida has seen 58 cases and five deaths, which are caused by a fatal swelling of the brain. That's an increase from past years, but still comparatively few. Last year, the epicenter of the disease was Illinois, with nearly 900 cases, while Florida had 28.
West Nile spreads to humans through bites from mosquitoes, which get the virus after biting infected animals such as birds or horses. Mosquitoes need water to lay their eggs and let their larvae hatch.
One theory for the low instances of West Nile is that weather patterns haven't helped it spread, said Jonathan Day, professor at the Florida Medical Entomology Laboratory of the University of Florida.
For the virus to amplify here, Florida's spring needs to be dry, so that mosquitoes and birds cluster together around shrinking water sources, Day said. Then the weather needs to become wet, so that the infected mosquitoes breed and roam the state.
The state had that weather pattern in 1977 and again in 1990, when there were epidemics of St. Louis encephalitis, another mosquito-borne illness, Day said. But 2001 and 2002 were too dry, while last spring was too wet, he said.
Another explanation could be that some of Florida's species don't bite humans. The mosquito wreaking havoc in Colorado is Culex tarsalis, an "avid feeder on people" that also travels more than most species, said Colorado veterinarian Sue Montgomery, an epidemic intelligence service officer studying the disease with Centers for Disease Control and Prevention.
Also, Florida may have fewer cases because it has more mosquito controls than most states, Montgomery said. Floridians are constantly advised to take precautions against mosquitoes, and regular spraying is common.
Still, Day warns that a future epidemic in Florida is possible, pointing out that older people are more likely than younger people to show symptoms of West Nile once they are bitten.
"If we have - and I think we will - an event comparable to Colorado's, we'll end up with easily 3,000 cases. And if you consider the age structure (of Florida's population), it may even be worse," he said.
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