The time frame is similar to last year's. The first report of West Nile in Nevada in 2004 came on July 16.

The virus spread to Clark County last year. Ultimately, there were 44 cases of the virus reported in humans statewide, with 25 found in Clark County. There were no deaths.

The news that West Nile has re-emerged in Nevada for a second year was used by state officials to remind residents to take preventive steps to avoid being bitten by mosquitos.

"The bottom line is, the West Nile virus is in Nevada," said Dr. Bradford Lee, state health officer. "Everyone needs to practice preventive measures such as, when outdoors, use insect repellent containing DEET; wear pants, long-sleeve shirts and socks; remove standing water from around your house; and make sure the screens on your doors and windows fit properly.

"People 50 years of age or older are more likely to develop serious symptoms of West Nile virus and should take special care to avoid mosquito bites," he said.

Increased Surveillance

The crow identified with West Nile was found dead and collected by an employee of the Mason Valley Mosquito Abatement District. A swab was taken from the bird's oral cavity and sent to the Agriculture Department's lab.

Ed Foster, a spokesman for the Agriculture Department, said the positive test means that health officials around the state now will increase surveillance looking to identify the geographic extent of the virus.

While it is possible the crow flew into the region from somewhere else, it is unlikely, he said.

"Birds are not migrating so much right now," he said. "They are staying around their food and water sources."

Foster said that anyone who owns a horse and has not had it vaccinated for the disease should do so.

Dr. Anette Rink, supervisor of the agency's Animal Disease Lab, said it was the first positive result after the testing this year of more than 1,500 mosquito pools, 40 dead birds and 36 horse samples.

'Dead-End Hosts'

West Nile first appeared in the United States in New York in 1999. Mosquitos pick up the disease from infected birds and transmit it to people, birds and other animals they bite. The virus causes fevers and aches and can lead to fatal swelling of the brain.

In about 80 percent of the cases, people do not even know they have the virus, said Martha Framsted, public information officer for the state Health Division. But in other cases, death or severe illness is a possibility.

The virus cannot be transmitted from human to human, or from horse to human, she said.

"Humans and horses are what are called 'dead-end' hosts," Framsted said.

So far this year, human West Nile cases have been reported in 15 states, including California and Arizona, according to the federal Centers for Disease Control and Prevention. California has reported nine cases, and Arizona five.

By Sean Whaley