Placer County is experiencing a record amount of West Nile virus detections in its mosquito and wild bird population this year. As of today, July 19, 2023, 66 positive mosquito samples and 10 positive dead birds have been detected in the county from rural west Placer, west Roseville, Lincoln, and Newcastle. Record rainfall from this spring leaving standing water throughout the county and high summer temperatures contribute to the increase in West Nile virus transmission risk.
Under these conditions, West Nile virus transmission risk from a mosquito bite is very high. The District is conducting wide-area adult mosquito treatments to reduce the number of infected mosquitoes in the environment. 
District staff will continue to aggressively treat immature and adult mosquito populations throughout the county to help continue limiting the risk of disease transmission to people over the following months
Residents can protect themselves by using a mosquito repellent with an EPA-registered ingredient like DEET or Picaridin when outside especially during dusk and dawn when mosquitoes are most active. Dump and drain all standing water that can contribute to mosquito development. For questions or concerns, contact our District at or (916) 380-5444.
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