Archived News

First West Nile Virus Found by UC Davis

August 20, 2003

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 theSalton 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 Nileor 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 studentsdiscovered 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 also serves as a regional reference center to confirm tests conducted in other laboratories.

The Center for Vectorborne Diseases 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

More information on today's announcement by the California Department of HealthServices, along with public safety tips, is posted at

Wister wildlife area map:

Media contact
* Sylvia Wright, UC Davis News Service, (530) 752-7704,

Additional contacts
* John Edman, UC Davis Center for Vectorborne Diseases, (530) 754-5520,
* Lea Brooks, California Department of Health Services Public Affairs, (916) 440-7660,