Encephalitis Alert Issued by Health Officials : Disease: The county deploys mosquito traps after the virus is found in chickens in the Los Angeles area.

Ventura County health officials issued an alert Thursday about a potentially deadly mosquito-borne virus that has turned up in Los Angeles County.

The virus, St. Louis encephalitis, is found in the blood of wild and domestic birds, such as chickens. It can be transferred to humans by infected mosquitoes, officials said.

“There is the possibility of fatal illness” from the virus, said Randall Smith, a county environmental-health specialist.

Smith and other officials said the virus has never been found in Ventura County, but officials are concerned because it turned up recently in “sentinel” chicken flocks in Los Angeles County. The flocks serve as an early-warning system for public-health officials. Among the areas where the virus surfaced were Monterey Park, Irwindale, Pomona and Wilmington.

Ventura County officials set mosquito traps Wednesday night in the Santa Monica Mountains and collected samples from the traps on Thursday. Suspected carriers of the virus are sent to a state lab in Berkeley for testing.

More traps will be deployed in the coming weeks in the Fillmore, Simi Valley and Thousand Oaks areas to ascertain whether the virus has been carried to Ventura County, the officials said.

The warning came during a season when mosquitoes have proliferated because of heavy rains.

In 1984, an outbreak of St. Louis encephalitis in Los Angeles County infected 16 people, killing one and contributing to the deaths of two others, according to health officials. Since then, health officials there have found isolated evidence that the virus still exists in Los Angeles County.

The virus is found in the blood of wild and domestic birds. Once mosquitoes feed on the infected birds, they can carry the virus to humans. However, the virus cannot be transferred from person to person or from birds to people, officials said.

St. Louis encephalitis causes an inflammation of the brain and nervous system. Usually the infection is mild and causes headaches, fever and nausea, officials said. But in more severe cases, confusion, paralysis, coma and even death can occur. The elderly are more susceptible to the virus than younger people.

Mark Westerline, manager of the Moorpark Mosquito Abatement District, the only district in the county designed to protect a specific city, said he is not apprehensive about the virus surfacing in Moorpark.

“It doesn’t sound like any reason for extra concern,” he said.

Leta Yancy, the abatement district’s executive secretary, said the 32-year-old agency was established because so many flies were attracted to the area’s chicken ranches.

“No one can realize how bad the flies were unless they lived here at that time,” she said. “Now we probably have less flies than anywhere in the world.”

The encephalitis warning came just two days after the county Board of Supervisors, reacting to the state budget crisis, slashed funding for dozens of county programs, including the Environmental Health Division.

Although the cut will not affect the county’s current efforts to control the pest, it might be felt next year.

“The reduction affects about one-fifth of our program,” said Bob Gallagher, manager of the Environmental Health Division’s resources section. “It will have a major impact on the work that they do.”

Gallagher said the two-page alert had nothing to do with the action of the supervisors.

“I prepared a draft of it last week,” he said.

How to Avoid Mosquito Bites Ventura County health officials recommend these steps to guard against mosquito bites, which can transmit St. Louis encephalitis: Stagnant water: Remove standing water from planters, old tires, cans, buckets and other places where mosquitoes breed. Make sure fishponds and swimming pools are properly maintained.

Night life: Avoid evening activities in mosquito-infested areas.

Proper attire: If you go out, wear appropriate clothing such as long-sleeved shirts and long pants, and use insect repellent.