SACRAMENTO - The first evidence of West Nile virus (WNV) in California this year has been found in mosquitoes collected in Imperial County near the Salton Sea, State Health Director Diana M. Bontá, R.N., Dr.P.H., announced today. Several flocks of sentinel chickens from the same region are also likely positive for WNV based on preliminary testing.

The testing of mosquitoes and sentinel chickens are part of the state's surveillance system for WNV and other mosquito-borne viruses. The blood tests indicate that the chickens, which are kept in flocks outdoors, were bitten by mosquitoes infected with WNV or a closely related virus, Bontá said. The mosquitoes were collected by the University of California at Davis and the Coachella Valley Mosquito and Vector Control District through a collaborative surveillance project. They were tested at the University of California arbovirus diagnostic laboratory in Davis, which is working in partnership with the California Department of Health Services (CDHS).

"California's surveillance system is working," Bontá said. "As West Nile Virus has moved westward across the nation, we have been preparing for its arrival."

Nationwide, WNV has been linked to a total of 715 illnesses and 14 deaths this year. In California, there have been no reported illnesses involving locally acquired WNV. Last week the state reported its first imported case of the virus in an Alameda County woman who had been bitten by an infected mosquito while visiting Colorado. The woman is suffering from acute flaccid paralysis, a rare neurologic syndrome, which is characterized by severe muscle weakness in her legs.

Last year, California's first reported human case of WNV was recorded in Los Angeles County. The woman fully recovered. Further WNV activity was not detected despite extensive monitoring for the virus. In the United States, more than 4,000 human cases of West Nile infection were reported last year, including 277 deaths. Since it was first detected in the United States in New York in 1999, WNV has been found in 44 states and the District of Columbia.

Most individuals who are infected with WNV will not experience any illness. Others will have only mild symptoms, such as fever, headache and body aches. Less than 1 percent of individuals, primarily the elderly and those with lowered immune systems, will develop serious illness such as encephalitis and meningitis.

WNV is transmitted to humans and animals through a mosquito bite. Mosquitoes become infected when they feed on infected birds. Human-to-human transmission of WNV generally does not occur. However, human WNV infection was associated with blood transfusions and organ transplants in 2002.

"With the arrival of West Nile Virus in California, it is more important than ever for Californians to protect themselves from mosquitoes," Bontá said.

Individuals can reduce their risk of mosquito-borne diseases by taking these precautions:

• Avoid spending time outside when mosquitoes are most active, especially at dawn and dusk.

• When outdoors, wear long pants and long-sleeved shirts.

• Apply insect repellent according to label instructions.

• Make sure that doors and windows have tight fitting screens. Repair or replace screens that have tears or holes.

• Eliminate all sources of standing water on your property that can support mosquito breeding.

• Contact your local mosquito and vector control agency if there is a significant mosquito problem where you live or work.

The comprehensive surveillance program to monitor for WNV in California has been established by CDHS in collaboration with the University of California, Davis, California Department of Food and Agriculture, local mosquito and vector control districts and other state and local agencies. The program includes testing suspect cases in humans and horses, capturing and testing mosquitoes, testing sentinel chickens and evaluating dead birds. Approximately 200 flocks of sentinel chickens at sites throughout the state are tested every two weeks for the presence of the virus.

The public can become part of the state's monitoring effort for WNV by reporting any crows, ravens, magpies, jays, sparrows and finches that may have been dead for less than 48 hours to a special CDHS toll-free line: 877-WNV-BIRD. Individuals should take note of the bird's location and its condition before calling for further instructions, including assistance with identifying the type of bird found. The bird should show no signs of decomposition or maggot infestation.

The tissue of dead birds is tested for the presence of WNV. The virus was most often identified first in dead birds, especially crows, in other regions of the country. While there is no evidence that people can get the virus from handling live or dead infected birds, individuals should not attempt to catch or handle them.

Since horses are susceptible to WNV and a vaccine is available for horses, horse owners are advised to contact their veterinarians about timely vaccinations.

For information about WNV or to report dead birds, visit the Web site: http://www.westnile.ca.gov/.

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