West Nile Virus Activity 2025
West Nile Virus in Los Angeles County
West Nile virus is the most common mosquito-borne disease that affects residents in Los Angeles County. Public health agencies detect West Nile virus every year in L.A. County which means it's endemic and found naturally in our city environments.
Our agency reports data related to mosquitoes. Human cases are reported by the L.A. County Department of Public Health.
The disease surveillance program serves as an early warning system in the detection of mosquito-borne viruses that can infect people and animals.
The District uses the following factors to assess health risk in your community:
- Higher-than-average daily temperatures
- Mosquito Population Monitoring – Using traps set up in every community
- Mosquito Testing for Diseases
- Dead Birds – A CA state program: Dead birds help determine spread of West Nile virus
- Sentinel Chickens – Chickens develop antibodies to West Nile virus, which can be detected by testing.
Using these measurements, the District is able to protect your health by responding appropriately to mosquito-borne disease threats.
Year-to-Date Statistics for 2025
2025 WNV+ Mosquito Samples
| City/Community | Date of First Detection | Positives |
|---|---|---|
| Arleta | 6/30/2025 | 1 |
| South El Monte | 7/02/2025 | 1 |
| Valley Glen | 6/30/2025 | 1 |
| Total | 3 |
Take a look at mosquito and disease activity throughout California by utilizing the VectorSurv map!
Did you know Los Angeles County is serviced by five vector control districts?
Visit our Other Agencies page to find your local vector control district.
