West Nile alert expands to Florida Keys

State confirms 4th case of virus

TALLAHASSEE, Florida (CNN) -- The Florida Keys are under a medical alert after state officials confirmed Friday that a 73-year-old woman contracted West Nile virus after visiting the area.

"It is believed that the woman contracted the disease while visiting Marathon in the Florida Keys last month," said a statement from the Florida Department of Health.

The woman is being treated for encephalitis -- a potentially fatal swelling of the brain -- which was caused by West Nile virus, according to health officials. She is in a Sarasota County hospital, near her home.

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It is Florida's fourth confirmed case of West Nile virus. Thirty-four out of 67 counties in the state are under a medical alert for the virus and others that can cause encephalitis.

Florida first discovered West Nile virus in a dead crow on July 6, and the first human case was confirmed two weeks later.

No Floridians have died from West Nile virus, said April Crowley, spokeswoman for the Florida Department of Health.

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In July, health officials confirmed that a nine-year-old boy died from Eastern equine encephalitis, which Crowley said is more dangerous than West Nile virus. However, health officials are testing for West Nile virus because it just recently spread to the Southeast, Crowley said. She said the prevention efforts the state is encouraging people to follow are effective on all viruses that lead to encephalitis.

People with weakened immune systems, especially the elderly, are more vulnerable to contracting West Nile virus, Eastern equine encephalitis and St. Louis encephalitis. The first case of West Nile virus in the Western Hemisphere was reported in the New York area in 1999. Earlier this month, a 73-year-old Staten Island woman tested positive for the virus, the first confirmed case in New York for 2001.

Mosquitoes feed on birds infected with the virus and then bite humans, spreading the illness. Earlier this month, health officials in Georgia confirmed that a 71-year-old woman died from West Nile virus, the state's first confirmed fatality from the virus.

On Thursday, Michigan state health officials said the virus has been detected in two dead crows, found just north of Detroit. No human cases had been identified. Residents in areas where West Nile virus has been detected are urged to avoid outdoor activities between dusk and dawn, when mosquitoes are more likely to bite; to wear light-colored long pants and long-sleeve shirts; to use mosquito repellent; and to get rid of stagnant water where mosquitoes might breed.