Authorities said they will work with state agencies to check for larval mosquitoes in standing water in the park and spray the areas with an oil-based substance to prevent the larvae from hatching into adult mosquitoes.

"We're not surprised by the finding because we've had dead birds this summer from the virus," said Dr. Anthony Billittier IV, county health commissioner.

The West Nile virus is spread by the bite of an infected mosquito and can infect people, horses, many types of birds and some other animals. Four infected birds have been found this year in Erie County.

Most people who become infected with the West Nile virus will have either no symptoms or only mild ones. On rare occasions, the West Nile virus infection can result in a severe and sometimes fatal illness known as West Nile encephalitis, an inflammation of the brain.

The risk of severe disease is higher for people age 50 and above. There is no evidence to suggest that the West Nile virus can be spread from person to person or from animal to person, according to health authorities.

Since its advent in North America with an outbreak in New York City in 1999, the West Nile virus has spread rapidly across the country.

Although human illness from the West Nile virus is rare, health officials here stressed the need to proceed cautiously, particularly with the fear aroused by the five deaths from the illness this summer in Louisiana.

So far this year in New York State, health officials have identified 176 dead birds and 80 mosquito pools infected by the virus. Erie County collects mosquitoes and their larvae for testing from 10 sites. There are more than 60 species of mosquitoes in New York State, but only a few of them can transmit the virus.

The county no longer collects dead birds, but officials said they want residents to notify the Health Department when they find a bird.

Adult mosquitoes are collected in specially designed traps. These specimens are transported to a laboratory in Albany where they are processed into "pools," a collection of adult mosquitoes of the same species and from the same location. A pool may contain hundreds of adult mosquitoes or only a few. Billittier estimated this pool at 50 mosquitoes.

In this instance, officials identified the pool as the northern house mosquito, Culex pipiens, found in urban and suburban areas. The female mosquito lays its eggs in any receptacle containing stagnant water such as tires, birdbaths, clogged rain gutters and plastic wading pools.

As such, officials encouraged residents to take steps to avoid trouble by keeping children away from mosquito-infested areas and ridding their lots of stagnant water.

"This is an opportunity to take common-sense precautions," said Deputy County Executive Carl J. Calabrese.