Each summer, surveillance for West Nile virus ramps up as the weather warms. The District uses three surveillance techniques to guard against West Nile virus (WNV) 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 monitor two District-owned flocks in 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

To date, no West Nile virus antibodies have been detected in sentinel chickens in San Mateo County.

Page last reviewed: July 10, 2024