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Placer County Reports Its First Human West Nile Virus Case Of 2011

September 19, 2011

A Roseville resident tested positive for the West Nile virus (WNV) recently, becoming the first person in Placer County this year to have a documented case of the disease. The resident became ill last month and tested positive for WNV after a hospital visit. Confirmatory testing was then done by the California Department of Public Health laboratory. This patient has since recovered.

West Nile virus is transmitted by the bite of a mosquito, usually in the two weeks before illness. Because of some travel out of the area, public health officials said the person could have been infected during that travel or in Placer County. However, they emphasized that this case, and the positive mosquitoes and birds found this season in the western County, reminds us that everyone should take precautions against the mosquito-borne disease.


“Because West Nile infections are preventable, we strongly urge residents and visitors alike to take some simple precautions to avoid mosquito bites,” said Dr. Mark Starr, the county Director of the Community Health, Clinics and Animal Services Division. “Late summer and early fall is when we typically have human cases in Placer County, so it is important to be vigilant in preventing mosquito bites even when the weather is cooling” he added.

The California Department of Public Health reported Wednesday that 37 people from 12 counties have tested positive for WNV during 2011.

Placer County recorded six human cases of WNV in 2008, none in 2009 and three last year.

So far this year, the Placer Mosquito & Vector Control District has reported three dead birds with WNV and 32 mosquito samples that tested positive for the disease in Placer County.

While almost 80 percent of those infected with WNV have no symptoms, about 20 percent of those infected experience mild to moderate flu-like symptoms, called West Nile fever, which may be prolonged.

Less than 1 percent will have severe illness related to their infection. People over 50 years of age and people with suppressed or compromised immune systems are more likely to become seriously ill. Anyone with symptoms such as high fevers, severe headaches and stiff necks should contact their health care providers immediately.

The Placer County Health and Human Services Department and the Placer Mosquito and Vector Control District offer the following reminders about preventing the spread of West Nile virus:

  • Drain standing water weekly, since that is where mosquitoes lay eggs. Check yards for water in old tires, flowerpots and bird baths.
  • Avoid mosquito bites by staying indoors at dusk and dawn when mosquitoes are most active and make sure that window screens are in good condition.
  • People who must be outdoors when mosquitoes are active should wear long sleeves and long pants, and use insect repellants that contain DEET, picaridin or oil of lemon eucalyptus.
  • Residents who know of swimming pools that are not being maintained are urged to report them to the district at 888-768-2343. Neglected pools are ideal breeding grounds for mosquitoes.
  • Concerned residents may request property inspections through the district’s website at or by calling 888-768-2343.
  • Residents also are encouraged to report dead birds by calling the California WNV hotline at 1-877-968-2473) or going online to
  • Horses are vulnerable to West Nile virus, and the mortality rate for unvaccinated horses is very high. Owners should contact their veterinarians about protective immunizations. West Nile does not spread between humans and horses.

For more information about WNV, call Placer County Community Health or visit

For information about mosquitoes and mosquito-control efforts, contact the district at 888-768-2343 or visit its website at