West Nile virus has been found in a sentinel chicken in Hillsborough County, marking the disease's sweep of the Tampa Bay area. State health officials now say the virus likely has infested the entire state of Florida.
The chicken, part of a flock off Fletcher Avenue kept to alert health officials to a variety of mosquito-borne diseases, was tested a week ago. Final results were made available Friday.
The virus was discovered last week in a sentinel chicken in northern Pinellas County. It also has sickened birds and horses in Pasco, Polk, Hernando and Citrus counties, so finding it in Hillsborough "isn't really surprising," said Dr. Carina Blackmore, a regional epidemiologist for the state Department of Health.
However, no dead wild birds have tested positive for West Nile in either Pinellas or Hillsborough, suggesting the virus is here in very low levels, she said.
Since July, West Nile virus has infected at least 10 people in Florida, none fatally and mostly in North Florida. It also has sickened more than 281 horses, killing almost one-third of them. An equine vaccine for West Nile is now available in most counties.
Experts say hundreds more people likely have been infected with West Nile but were never diagnosed. In most people it causes mild flu-like symptoms for several days. But in the sick, elderly or very young, it can cause encephalitis, a swelling of the brain that can lead to brain damage or death.
Blackmore said state health officials now think the virus is present throughout the state, even in counties where it hasn't been confirmed. It has been confirmed in every county along the Georgia border, most counties in Central Florida, and in the Keys.
It continues to be most active in North Florida, where "we have a lot more dead birds, a lot more horses, a lot more positive chickens," Blackmore said.
Although West Nile doesn't hurt the sentinel chickens, it does kill several species of wild birds, including blue jays, mockingbirds and crows. People who find dead birds were asked to call their local health department.
West Nile is native to Africa and the Middle East and was first found in the United States in 1999, when it killed nine people in the New York metropolitan area. It has marched steadily south since and was first discovered in Florida early this summer.
One person, a woman in Atlanta, died of West Nile this summer.
The cool weather of winter typically reduces Florida's mosquito populations, which also reduces the spread of native mosquito-borne diseases such as Eastern equine encephalitis and St. Louis encephalitis.
Since West Nile is new here, health officials don't know how it will act over the winter, Blackmore said, but "we have no reason to think this is going to be different."