West Nile Virus Found in State

Health authorities have found the West Nile virus in mosquitoes near the Salton Sea, the first evidence that the disease is developing reservoirs in California.

In addition, preliminary tests, also in Imperial County, showed that several flocks of chickens whose blood is regularly tested for disease are likely to have the virus as well.

The discoveries suggest that human cases of the disease may soon follow, as has happened in other states.

“We knew it was coming, we’ve watched it migrate west,” said Robert Miller, a spokesman for the California Department of Health Services. “Now it’s here.”

Until Tuesday afternoon, when the virus was detected, state health officials had been unable to pinpoint any local sources for the disease.

A Los Angeles County woman was diagnosed with West Nile last year; it was suspected to have been acquired locally but the source of the illness was never determined. Other cases in the state last year occurred in residents infected outside California.

Last week the state reported its first imported case of the virus this year in an Alameda County woman who had been bitten by an infected mosquito while visiting Colorado.

The West Nile virus has spread to humans or animals in most states, with 39 states and the District of Columbia reporting illnesses in humans, according to the Centers for Disease Control and Prevention.

The CDC’s current map charting the westward spread of the disease shows the gradual arrival of infected mosquitoes and birds.

Only Nebraska in the Midwest and the Western states of Washington, Idaho, Nevada, Hawaii and Alaska remained unaffected. In the rest of the country, only Rhode Island is free of the virus.

Nationwide, West Nile virus has led to 715 infections, with 14 deaths this year. According to the CDC, Colorado has been hit particularly hard, with 262 cases, while South Dakota and Texas have had 66 cases and Nebraska 55.

Near the Salton Sea on Tuesday, the virus was detected during routine testing of mosquitoes and sentinel chickens as part of the state’s surveillance system for West Nile and other mosquito-borne viruses. The mosquitoes were collected by UC Davis and the Coachella Valley Mosquito and Vector Control District.

West Nile infects birds, mainly crows and ravens, that are bitten by mosquitoes. Mosquitoes become carriers by biting infected birds, then passing along the virus to humans.

Only 20% of people bitten by infected mosquitoes become ill, according to the CDC, experiencing mild symptoms, including fever, headache, body aches, a skin rash on the trunk of the body and swollen lymph glands.

Elderly people appear to be the most vulnerable, but fewer than 1% of people with the virus develop serious illnesses such as encephalitis or meningitis.

Los Angeles County health officials said that although no insects or animals are infected here, doctors should be vigilant for signs of the virus in patients.

“We are alerting emergency room physicians throughout the county that the virus has been found and that they should consider West Nile as a diagnosis if appropriate,” said Jonathan Fielding, director of public health for the county Department of Health Services.

People should avoid mosquito-infested areas at dawn and dusk, empty pools of stagnant water and wear long sleeves and pants, Fielding said.