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Virus Surveillance

mosquito trap

The District conducts annual surveillance for mosquito-borne encephalitis viruses by maintaining five flocks of 'sentinel' chickens (located in Hercules, Martinez, Oakley, Walnut Creek and Knightsen). Blood samples from these chickens are tested biweekly May through October for antibodies to encephalitis viruses. Our flocks are part of a statewide network operated in cooperation with the California Department of Public Health (click here for the latest statewide surveillance data).

We also use carbon dioxide (C02) traps (pictured) baited with dry ice (which simulates the breath of an animal) to collect live mosquitoes for virus testing. These traps are operated weekly April- October and biweekly November through March. We also use these battery-operated traps to monitor mosquito populations in remote areas where there is no electricity available for our New Jersey traps.

The District appreciates Contra Costa county residents reporting dead birds, which are an early indicator of West Nile virus activity. Certain bird species, especially corvids, are susceptible to the virus (and succumbing to it), and they are important for monitoring virus activity in specific areas. Reports can be made by calling 1-877-WNV-Bird or online.