Surveillance for West Nile virus begins in California each year in April. The District protects residents from this mosquito-borne disease with control that targets mosquitoes in the larval stage, mosquito population monitoring, disease surveillance and public education. The laboratory staff conduct surveillance to detect the presence of mosquito-borne disease by testing dead birds and trapped mosquitoes.

Dead Bird Surveillance

The District collects dead birds that are reported by residents. Dead birds should be in good condition without signs of decay or trauma. Birds except water fowl, poultry or pigeons are collected and tested.

To report a dead bird, residents should call the state West Nile virus hotline at 1-877-WNV-BIRD (1-877- 968-2473), which opens with live operators in mid-April each year. Online reports can be made at westnile.ca.gov.

Mosquito-borne Disease Testing

The District laboratory tests mosquito samples for West Nile virus, Saint Louis encephalitis and Western equine encephalitis.  Samples tested include whole mosquitoes for the presence of these viruses.

Page last reviewed: February 19, 2025