Relying on tests conducted by the University of California, Davis, the California Department of Health Services today announced the first evidence of West Nile virus in the state this year.

The UC Davis tests showed that mosquitoes collected in Imperial County near the Salton Sea were carrying the virus. The mosquitoes were collected by UC Davis staff researchers in the Wister Unit of the Imperial Wildlife Area, on the southeast rim of the Salton Sea. They were tested by laboratory staff members at the UC Davis Center for Vectorborne Diseases.

The state health department also said that preliminary tests at state laboratories showed that flocks of sentinel chickens from the same region are likely infected with West Nile Virus. The blood tests indicate that the chickens, which are kept in flocks outdoors, were bitten by mosquitoes infected with West Nile or a closely related virus, the health department said.

The Department of Health Services coordinates statewide efforts to prevent the spread of the virus and to watch for it in mosquitoes, wild birds, sentinel chickens, horses and humans.

UC Davis, with the largest West Nile research and testing programs in the state, is fundamental to those public-health efforts.

"During the 2003 season we have tested more than 5,000 groups of 1 to 50 mosquitoes each, as well as tissue samples from birds and other animals, for the presence of West Nile virus," said John Edman, director of the Center for Vectorborne Diseases and a UC Davis professor of medical entomology. "All were negative until Tuesday, when we discovered West Nile virus in this group of 27 Culex tarsalis mosquitoes we collected near the Salton Sea."

(UC Davis researchers recently showed that Culex tarsalis is the species, of some 200 mosquito species in the United States, which transmits West Nile virus most effectively. UC Davis professor of entomology Thomas Scott and his students discovered that C. tarsalis can spread the virus most efficiently to hosts such as birds, horses and people. A significant proportion can pass the the virus through its eggs to its offspring.)

The UC Davis Center for Vectorborne Diseases performs the tests for the state of California to detect West Nile virus in samples from mosquitoes, wild birds, horses and other animals. Samples from sentinel chickens and humans are tested for viral antibodies in the state laboratories in Richmond.

The Center for Vectorborne Diseases, which serves as a regional reference center to confirm tests conducted in other laboratories, is a program of the UC Davis School of Veterinary Medicine.

The mosquito collection work in this instance was funded by the Coachella Valley Mosquito and Vector Control District.

UC Davis has experts on a broad range of topics concerning West Nile virus, including how the virus is expected to spread in California; West Nile and related viruses such as St. Louis encephalitis and western equine encephalitis in humans, horses, livestock and wildlife; how viruses in general are transmitted; the rise of new ("emerging") viral diseases; and mosquito control methods.

Those experts are listed at http://www-news.ucdavis.edu/search/news_detail.lasso?id=6590.

More information on today's announcement by the California Department of Health Services, along with public safety tips, is posted at http://www.dhs.ca.gov.

Wister wildlife area map: http://www.saltonsea.ca.gov/birding.htm.

Note to news media: John Edman is available for interviews today. The Davis laboratory will be open for interviews, photography and filming on Thursday, Aug. 21, from 9 a.m. to 10 a.m. Researchers will demonstrate how mosquito and other samples are tested for West Nile virus. Live mosquitoes used in research projects will be fed a blood meal.

Directions: Take Interstate 80 to the UC Davis exit, just east of Highway 113. Travel south (away from the main campus) on Old Davis Road. Turn left at the second driveway after the railroad tracks. Watch for signs marked "West Nile Media." Please be on time; lab access cannot be given after 10 a.m.