It's time for local equine owners to take West Nile virus seriously and vaccinate their steeds. Horses in Paso Robles, Creston, and Arroyo Grande are some of the latest victims of the mosquito-borne illness. On Aug. 24, one of the three infected horses died from the virus.

The California Farm Bureau Federation noted that, according to the California Department of Food and Agriculture, Lake, Mendocino, and Modoc counties also recently reported their first equine West Nile cases of the year.

At the time of the report, horses in 14 California counties had come down with the disease, and 11 horses had died. Still, the number of cases remains much lower than it was in the last two years.

Thus far, there has been only one confirmed human case in San Luis Obispo County in the past three years, said Curt Batson, director of SLO County Public Health Department's Environmental Health Services.

"Last year, we had total of 13 infected horses, and so far this year we've had three," Batson said. "We also have fewer dead birds than last year's 41 and this year only four. People have speculated the possibility that immunities in horses have been built up, more horses have been vaccinated, there are fewer birds this year, or greater interest in mosquito abatement as possible reasons for the decline."

Mosquitoes that have fed on birds harboring the disease can infect horses and humans. While the insect's two-legged victims must resort to bug spray, staying indoors, or wearing long sleeves to avoid infection, a vaccine for horses has been available for approximately two years. Infected people and horses are not contagious.

Though numerous reports claim that up to 50 percent of infected horses perish from the illness, there are currently no studies of horses not showing symptoms to support these assertions, according to the Center for Disease Control. However, approximately 80 percent of people infected by West Nile virus display no symptoms.

Still, new cases of West Nile virus are mounting as summer wanes along the Central Coast. Birds in Paso Robles, Santa Margarita, and Carpinteria have tested positive this summer. County officials are suggesting that horse owners drain and replace water in troughs and barrels once a week and consider vaccinating their stock.