ROSEVILLE, Calif., August 2, 2012 – Twenty-two additional mosquito samples in Placer County have tested positive for West Nile virus (WNV) in the past week, all occurring on the western side of the county, from Sheridan in the north, down to the southern border of Roseville.  The Placer Mosquito and Vector Control District also reports four WNV-positive dead birds collected in the past two weeks.

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

Due to this latest development, the district has mounted 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 and has 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,” explains Sorensen.  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 currently the Placer Mosquito and Vector Control District is in emergency planning stage, according to Sorensen.

The Placer Mosquito and Vector Control 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 further encourages residents to talk to their healthcare providers 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

2012 Placer County West Nile virus activity update: 5 dead birds, 0 sentinel chickens, 37 mosquito samples, and 0 humans have tested positive for West Nile Virus to date