UF researchers on the watch for nice weather - and the diseases it could bring

March 19, 2008

GAINESVILLE, Fla. — Calling it a silver lining may be a stretch, but the storm clouds wrought by the devastating 2004 hurricane season did bring the Sunshine State at least one ray of relief.

The year before, West Nile virus unexpectedly struck nearly 3,000 people in Colorado, killing more than 60. Similar outbreaks seemed virtually inevitable throughout the country for the next year — especially in Florida, where the mosquito and bird-borne disease seemed inevitable.

Even after months of preparation, states such as California, Arizona and Texas suffered heavy casualties in 2004. In Florida, however, four major hurricanes and a tropical storm had splattered mosquito and bird populations across the state, leaving the virus no means of reproducing and spreading.

Meteorological challenges continued to hold the virus at bay for the next three years — another heavy hurricane season followed by two years of drought. But this year, the weather could actually be “normal,” and University of Florida entomologists could think of no scarier proposition.

Already this season, high levels of eastern equine encephalitis virus have been documented in parts of Central Florida. These early outbreaks may not bode well for the upcoming mosquito season.

“Depending on the summer rainfall patterns, conditions in Florida could be perfect for us to finally be hit by some of the diseases we’ve been narrowly ducking the last few years,” said Jonathan Day, professor of medical entomology at UF’s Medical Entomology Laboratory in Vero Beach, part of UF’s Institute of Food and Agricultural Sciences. “We’re watching very closely so we know what to prepare for.”

As Day outlines in a paper published in this month’s Journal of Medical Entomology, there is a distinct chain of events that leads to a Colorado-like epidemic, and that chain begins in early January with specific rainfall, drought and temperature patterns.

For example, a series of droughts such as those reported in peninsular Florida during the last two years, could isolate mosquitoes into small areas of moisture-rich land. During that time, the confined mosquito population interacts with the birds that are attracted to the fresh water. The birds and mosquitoes become a captive audience and cycle any virus that is trapped in that space with them.

When rains return, the now infected mosquito population would then be set free to spread the disease to other birds and animals, including humans, on which they feed.

There are currently more than 560 meteorological recording stations across Florida carefully monitoring the Sunshine State’s weather patterns.

Many in the state may already be feeling the buzzing pests’ bites, but the information gathered at the recording stations and by many other experts across the state allow an analysis of what the current conditions may mean for July — the bloom of mosquito season and potentially the most dangerous time for arboviral diseases.

Of course, mosquito-borne diseases have probably been a problem since humans first inhabited the state of Florida 15,000 years ago. However, the increasing density of the human population in Florida makes the problem far more potent, Day says.

For example, widespread outbreaks of St. Louis encephalitis virus struck peninsular Florida in 1977, with 110 human cases. Thirteen years later, it struck again with 226 cases.

In his paper, Day points out how both outbreaks followed strikingly similar rainfall and drought patterns, patterns that can be tracked and are predictive of future mosquito-borne disease outbreaks.

But, of course, the crystal ball isn’t only focused on weather patterns. Knowing which mosquito species are dangerous is also vitally important.

“The type of mosquito not only tells us what kind of disease we could be dealing with, but also when and how to take precautions,” said Roxanne Rutledge Connelly, a UF entomologist who helps teach one of the most recognized courses in identifying mosquitoes in the world.

For example, if the potentially dangerous mosquito population is the Asian tiger mosquito — a relatively new invasive species to the United States known for spreading dengue fever in Hawaii and Southeast Asia — then the game is completely different than that for the vast majority of other mosquito species.

The Asian tiger mosquito not only feeds in bright sunlight, but it needs significantly less water to breed than most of its American cousins. So, control and prevention programs must consider these issues.

“We have more ability now than ever before for predicting these outbreaks and doing something about them before they get out of hand,” Day said. “There are vaccinations, animal control measures and insecticides. The truth is that our best tool is still general public awareness; but it’s the most difficult tool of all to put into use, because it takes the most time, effort and preparedness.”