West Nile Virus
West Nile virus (WNV) is a potentially serious illness. It is the most common and serious vector-borne disease in California. There have been more than 7,000 human cases and over 300 deaths reported in California since 2003. Mosquitoes that spread WNV are found throughout California.
WNV has been established as a seasonal epidemic that generally runs June 1 to Nov. 1. Click on this interactive map to view reported WNV cases across California.
How WNV IS Spread to Humans?
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 does not occur. However, human WNV infections have been associated with blood transfusions and organ transplants.
Control Activities in Alameda County
As of January 23, 2023, California reported 186 dead birds and 3,165 mosquito pools that tested positive for West Nile Virus in 27 counties. There also were 170 human cases statewide of WNV, and no human deaths. In Alameda County, 17 dead birds and 15 mosquito pools tested positive for WNV, with no human cases. No WNV activity was detected in 2022 in Alameda County, but ACVCS has confirmed detection of WNV positive mosquito as of January 31, 2023.
During WNV season, Alameda County’s Mosquito Abatement program works to limit risks to residents by monitoring ponds and other possible mosquito breeding sites; trapping to detect high numbers of mosquitoes; treating sewer catch-basins to prevent breeding; collecting birds for testing; and educating residents and owners about removing standing water from private property to limit mosquito breeding and mosquito bites.