West Nile Virus Activity Shows No Signs of Slowing Down

Release date: 
Sep 20

Cotati, CA-Residents in Marin and Sonoma counties may want to think twice before putting away that insect repellent as West Nile virus activity in the local mosquito population increases. The Marin/Sonoma Mosquito & Vector Control District (MSMVCD) has confirmed two more West Nile virus (WNV) positive mosquito samples in Sonoma County. One mosquito sample was collected from Cloverdale, in the vicinity of Citrus Fair Drive and Asti Road, and the other from Santa Rosa, in the vicinity of Millbrae Avenue and Langner Avenue.

In addition to the positive mosquito samples, five dead birds have tested positive for WNV (three from Sebastopol, one from Healdsburg, and one from Forestville) and two Marin County residents have been diagnosed with the virus (one from Tiburon and one from Fairfax). 

"Both residents that tested positive had travel history to areas with high West Nile virus activity, making it likely they may have contracted the virus elsewhere," stated Nizza Sequeira, Public Relations Director for the Marin/Sonoma Mosquito and Vector Control District. "However, we have increased our surveillance measures in all areas where the virus has been detected, including near the Marin County residents' homes."

Residents are urged to report mosquito problems in their areas and to reduce mosquito production sites in their yards by removing standing water on a regular basis.  Most importantly, residents should use personal protection measures against mosquito bites. Wearing long sleeved shirts, long pants and applying an effective repellent to exposed skin will help reduce the risk of WNV transmission from an infected mosquito.

Simple ways to help reduce exposure to mosquitoes and lessen the risk of WNV:

  • Eliminate standing water in rain barrels, old tires, buckets, kiddie pools or any other item that can hold water for more than 72-96 hours. 

  • Check septic tank lids to ensure a tight seal and repair any visible cracks.

  • Screen septic tank vent pipes using a fine mesh screen.

  • Report mosquito problems, neglected swimming pools, or any area that could be producing mosquitoes at www.msmosquito.com or 1-800-231-3236.

  • Stock backyard ponds or other permanent water features with mosquitofish. The fish are free and can be delivered or simply picked up at the district office.

  • Report dead birds to the West Nile virus hotline at 1-877-968-2473 or online at www.westnile.ca.gov.

  • Wear mosquito repellent when outdoors at dusk and dawn. Use a repellent containing one of the following active ingredients: DEET, Picaridin, oil of lemon eucalyptus, or IR3535. 

  • Residents interested in staying informed about district activities are encouraged to follow MSMVCD on twitter and facebook.

West Nile virus is a mosquito-borne disease that is spread by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread the disease to humans and other animals.


Less than 1% of people (about 1 in 150) infected with WNV develop serious illness. These cases may last for extended periods of time, result in permanent neurological damage and may be fatal.  

Approximately 20% of people (about 1 in 5) infected with WNV experience mild symptoms that may include fever, headache, body aches, nausea, rashes, swollen lymph nodes and vomiting. Approximately 80% of people (about 4 out of 5) infected with WNV do not show any symptoms.