And those precautions are considered wise, as a federal health expert recently reported that the state could expect a major outbreak of West Nile as early as next summer.

Dr. Lyle Peterson, the acting director of vector-borne diseases for the federal Centers for Disease Control and Prevention, reported in early October that the mosquito-borne virus could be expected to show up in great numbers all along the West Coast in 2004.

And, while the hardest-hit areas are expected to be California's San Joaquin Valley and the Imperial Valley, Peterson said, local equine owners are not taking any chances.

"We've been inoculating horses for two years now," said veterinarian Dr. Bill Seals, from Tri-County Vets in Gilroy, who is one of the veterinarians used by Calero Ranch Stables on McKean Road. "We've had a lot of opportunity to observe what the disease has done in other parts of the country."

Veterinarians and county vector-control officials are recommending to horse owners that they have the vaccine administered to their horses before the spread of the virus reaches local regions.

"We can't emphasize it enough—get [horses] vaccinated," said Kriss Costa, spokesperson for the Santa Clara County Vector Control Department. "The big thing is to vaccinate horses now. The main reason is there are two shots given four weeks apart, and you are still looking at four weeks before you get the full effect. If someone lives in a high mosquito-populated area, we recommend getting it done every six months."

Laurie Campbell, Calero Ranch Stables office manager, who also boards her own horse at the stables, said all the horses at the stables are inoculated, including the boarded horses.

"We're all concerned, but that's why we all do the preventive measures," Campbell said.

Down McKean Road from Calero Ranch, at Lightfoot Boarding Stable, stable manager Judith Ogus said that most people have immunized their horses.

"We don't make people do it, we're just recommending it," she said. "We're having a shot clinic on Oct. 25."

The vaccination has proven to be successful, Seals said, with about a 95-percent effective rate. However, it is not a guarantee that a horse will not become infected, and he said that 1 in 20 of those will still get the disease.

Humans and horses can contract the disease, but cannot transmit it, he said.

"It's a dead-end host in a horse," Seals said. "It cannot give it to anything else. The viral concentration does not get great enough in our bodies to shed it."

Evidence of the disease in horses is varied, ranging from flu-like characteristics to colic, but the most common symptoms are neurological.

"The biggest thing we see in horses is encephalitis," Seals said. "They go down and can't get up and can't eat."

Costa said in addition to the encephalitis, a condition causing swelling of the brain, other symptoms have included stumbling, wandering around or circling, muscle twitching and a weakness in the hind area.

The Centers for Disease Control says that only a small percentage of infected humans and horses become seriously ill or die. In humans, one in 150 people infected will become seriously ill, and 80 percent of infected people will show no symptoms at all.

Officials predict the virus will show up in large numbers in California sometime in 2004 through the far northern and southern reaches of the state, and travel, via infected birds and mosquitoes. Two people in Southern California have already been diagnosed with homegrown cases of West Nile.

"I'm a little surprised we haven't seen problems with it yet this year," Seals said about the lack of cases in the Bay Area. "I kind of expected them to appear this year, considering how fast it spread."

The disease spread quickly westward across the United States after arriving on the East Coast in 1999. It is spread to humans and animals through the bite of an infected mosquito. Mosquitoes can become infected by biting birds infected with West Nile.

Inoculations are not the only steps horse owners can take to protect their stock against mosquito bites, though. Fly sheets, a netting-type covering that can also come pre-treated with mosquito repellent, can be placed on the horse like a blanket or clothing.

Costa recommends using fans inside the barn where horses are kept, because mosquitoes don't like to fly in blowing wind.

She also suggests keeping grass and other vegetation trimmed down around the barn, because mosquitoes will rest in taller, cooler grassy areas.

Water troughs can be a breeding ground for larvae, so Costa recommends either changing the water frequently—it takes only a few days for larvae to hatch—or adding small, inch-and-a-half-long mosquitofish to the trough. Mosquitofish feed on mosquitoes and are otherwise harmless. They can be obtained for free from the Santa Clara County Vector Control Department.

Standing water in buckets, tires, planting pots or other receptacles should be eliminated.

The county vector control department tracks and tests dead birds found in the area. Costa said people should report any dead birds, and they especially look for ravens, crows, blue jays, hawks and sparrows.

The state's West Nile virus hotline is 877.WNV.BIRD and the Santa Clara County Vector Control Department number for reporting dead birds is 408.792.5010. For more information on the West Nile virus or mosquitoes, go to the county vector control website at http://www.sccvector.org or the Centers for Disease Control website at http://www.sccvector.orgwww.cdc.gov.

How contracted: The virus is spread by mosquitoes and can infect birds, horses, other animals and people.

Symptoms: Most of the time, it results in a flu-like illness with fever, headache and muscle pain lasting for two or three days. In severe cases, West Nile causes a potentially fatal brain inflammation. The elderly and people with compromised immune systems are most at risk. People who have symptoms and know they have been bitten by a mosquito should contact their physician.

Prevention: There is no vaccine approved for humans. The best prevention is to avoid being bitten by mosquitoes and eliminate standing water where mosquitoes can breed.

Source: Centers for Disease Control and Prevention; Santa Clara County Vector Control District.