Experts call virus no reason to panic

The mosquito-borne West Nile virus is likely to appear in west-central Florida, but it poses little risk to humans.

By WES ALLISON

© St. Petersburg Times,
published August 12, 2001

TAMPA -- Dr. Lillian M. Stark keeps a can of Off! by the door to her porch, and she spritzes it on to keep the mosquitoes at bay when she heads into her yard.

She has done that for years, and that's all she'll do when she finds the first trace of the West Nile virus in the Tampa Bay area.

As West Nile buzzes south, Stark, who oversees testing for mosquito-borne viruses in Florida at the state laboratory here, says it's only a matter of time before West Nile is found in birds, horses and perhaps even people in the Tampa Bay area.

But when it is, experts stress, there's no reason for people to panic.

"They have to put it in perspective," said Stark, supervisor of virology at the Florida Department of Health's Bureau of Laboratories in Tampa. "But they are responsible for preventing themselves from being bit."

This week, the state Health Department extended the medical alert for West Nile and eastern equine encephalitis, a more deadly native mosquito-borne disease, to include a total of 29 counties in North Florida. That means the viruses are in those areas and residents should try to avoid being bitten.

Even beyond the warning areas, people should take precautions. Dr. Steven Wiersma, acting director of the state's Bureau of Epidemiology, said there's no reason to stay indoors, but avoiding mosquitoes is always a good idea.

Wiersma, whose office is in Tallahassee, said parents have asked what precautions they should take before sending their children back to school.

"If I had my children in an after-school program where they're going to be playing outside, I would send them with some mosquito repellent," he said.

Experts say the virus could cover the rest of Florida any time and already may be in this area.

A horse in Pasco County is suspected of having the virus, and officials are awaiting final test results. Tampa Bay-area doctors have been advised to look out for human cases, and residents should report dead birds to their local health departments.

"It's on everybody's mind, and nobody wants to miss a case," said Dr. John Sinnott, director of infectious diseases at the University of South Florida College of Medicine and Tampa General Hospital.

Even if you're bitten by an infected mosquito, West Nile is rarely serious. Two Madison County residents, a 64-year-old woman and a 73-year-old man who live within 2 miles of each other, have been hospitalized with it in the past month, but scores more in North Florida likely have been infected and didn't even know it, state health officials said.

West Nile was discovered in the United States in summer 1999, when it killed nine people in the New York metropolitan area. In a recent study published in the British medical journal Lancet, researchers who conducted household surveys and blood tests soon after the outbreak found that as many as 8,200 residents had been infected, but they either didn't know or did not seek treatment.

The disease has since moved steadily south with migratory birds, but no serious human cases were reported until S.T. Carruthers, 73, a retired mechanic in the Madison County hamlet of Sirmans, was infected in July. It was determined last week that a Madison County woman also has the virus. Both appear to be recovering.

State epidemiologists, entomologists and veterinarians now are trying to determine which birds are the best hosts and which mosquitoes transmit the virus.

Crows and blue jays are infected easily, but it kills them in days, so they probably aren't good hosts, explained Robin Oliveri, a surveillance coordinator for the state Bureau of Epidemiology.

For West Nile to thrive, it needs a bird that can survive while carrying it. Stark's lab has tested more than 1,200 dead birds shipped in from around the state. About 30 have tested positive, including crows, blue jays, finches and a hawk.

Florida has about 65 species of mosquitoes. This week, the U.S. Centers for Disease Control found West Nile in three species in Jefferson County, including Culex nigripalpus which is common here.

"That's not good for us at all," Oliveri said. "It would have to be the birds that brought it to the area, but if nigripalpus is capable of being infected, it will definitely take root."

The nigripalpus also happens to be the primary vector for St. Louis encephalitis, a cousin of West Nile that has been in Florida for years and is much more dangerous.

No human cases of St. Louis encephalitis have been reported this year, although it was found in a sentinel chicken in Hillsborough County last week. St. Louis encephalitis outbreaks usually occur every four to seven years.

Some experts, including Sinnott, suspect West Nile arrived in Florida last year but took a year to reach detectable levels in populated areas. Florida's warm climate, swamps and large population of migratory birds make for an ideal environment.

"One of the important things (this) tells us is infectious diseases can be transmitted around the world very easily," Sinnott said. "It's established in the United States and it's never going to go away."

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