The first evidence of West Nile virus (WNV) in California this year was found in mosquitoes collected in Imperial County near the Salton Sea, announced Diana M. Bontá, RN, DrPH, state health director,  on Aug. 20. 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, 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.” This year in California, there have been no reported illnesses involving locally acquired WNV.

Last year, California’s first reported human case of WNV was recorded in Los Angeles County. Further WNV activity was not detected despite extensive monitoring for the virus