West Nile virus dead bird infections by county for California 2025

(2025-07-19) - Source: http://westnile.ca.gov

*Birds reported as "chronic" do not have sufficient virus to cause mortality from WNV. Similarly, these birds do NOT indicate recent WNV transmission in the county and they cannot spread WNV to mosquitoes or other animals.

Birds reported as "positive" have high levels of virus, indicating the bird was recently infected with WNV. They are an indicator of current WNV in the county.

Results are determined by molecular testing of bird tissues.

More information:

CountyPositiveChronic*Total
Alameda505
Contra Costa101
Fresno606
Kern101
Sacramento505
San Diego909
San Joaquin202
Santa Clara17017
Tulare505
Totals: 51051

Source: Vector-Borne Disease Section, California Department of Public Health