West Nile virus dead bird infections by county for California 2025

(2025-09-24) - 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
Alameda606
Colusa101
Contra Costa303
Fresno11011
Kern101
Lake101
Los Angeles404
Orange202
Placer707
Sacramento27027
San Diego24024
San Joaquin707
Santa Clara25025
Solano202
Sonoma101
Stanislaus101
Sutter101
Tulare808
Ventura101
Yolo404
Totals: 1370137

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