ROSEVILLE (CBS13) – Placer County is getting close to an epidemic level of West Nile Virus activity after 22 more samples tested positive this week and four dead birds were also found to be infected.

All the samples were found on the western side of the county, from Sheridan in the north down to the southern border of Roseville.

“This is the most virus activity we have seen all year. We are very concerned about these results, since some of the infected mosquitoes we’ve found have been very close to residential areas,” stated Dr. Mary Sorensen, entomologist and laboratory director for the Placer Mosquito and Vector Control District.

To date the district has reported finding five dead birds and 37 mosquito samples positive for the virus. No humans have tested positive.

Sorensen said this is the most activity she has seen in one week since she started at the district in 2009.

The district is conducting an “all-hands-on-deck” response, with technicians currently focusing on draining and clearing areas that have accumulated standing water around the West Nile virus hotspots. There are scheduled treatments for adult and larval mosquitoes for the next few days.

“We are not quite at the epidemic stage, but we are fairly close,” Sorensen said.

The district follows the California Mosquito-borne Virus Surveillance and Response Plan, which assigns values to key virus activity indicators such as number of WNV-positive mosquito samples and dead birds.

These values determine the stage of the epidemic and appropriate level of response, and the district is in emergency planning stage, according to Sorensen.

The district advises the public to implement the “3 Ds” of protection:

  • Drain any standing water that may produce mosquitoes.
  • Defend yourself and your home by using an effective insect repellent and dressing protectively when outside, and making sure screens on doors and windows are in good condition.
  • Contact the district for any additional help controlling mosquitoes around your home.

The district also advises residents to seek medical attention if they have a history of mosquito bites and are experiencing symptoms of West Nile virus, which can include fever, headache, body aches, nausea and vomiting.

For more information, contact the Placer Mosquito and Vector Control District at (888) 768-2343 or visit


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