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Current West Nile Virus Information for San Mateo County

May contain: animal, bird, chicken, fowl, poultry, and hen
A 2023 flock of young sentinel chickens explore their coop in East Palo Alto.

2023 Season

West Nile virus season has begun in California and surveillance for the disease is ramping up as the weather warms. The District uses three different surveillance techniques to guard against West Nile virus outbreaks: trapping adult mosquitoes, collecting dead birds, and monitoring two sentinel chicken flocks. Chickens are useful for WNV surveillance because while they can be infected with WNV, they do not become sick and die which means they can be tested regularly for evidence of exposure. District vector ecologists Tara Roth and Arielle Crews picked up 14 sentinel chickens on April 27 to establish two flocks in the cities of East Palo Alto and San Mateo. From April until October laboratory staff will take blood samples from the chickens every other week.  These samples are tested for antibodies against West Nile virus, western equine encephalitis virus, and Saint Louis encephalitis virus. If present, these antibodies in the chicken blood will inform us that these viruses are circulating in the area and allow us to take further steps to protect the public.

West Nile Virus Dead Bird Hotline

Would you like to help us protect against mosquito-borne illnesses? The California Department of Public Health’s West Nile virus call center is now open with live operators. Residents who find a dead bird in good condition (head and eyes intact and not infested with flies or ants) should call 1-877-WNV-BIRD (1-877-968-2473) or file a report online at If suitable for testing, a District staff member will bring the bird back to the lab and test the carcass for the presence of mosquito-borne disease.

Date last reviewed: May 5, 2023

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