West Nile virus dead bird infections by county for California 2026

(2026-08-28) - 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
Alameda34034
Contra Costa909
Fresno303
Los Angeles91091
Madera202
Merced202
Napa101
Orange36036
Placer707
Riverside303
Sacramento1010101
San Bernardino12012
San Diego34034
San Joaquin505
San Mateo909
Santa Clara90090
Solano202
Sonoma101
Sutter303
Ventura606
Yolo14014
Yuba303
Totals: 4680468

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