West Nile Virus Update For Marin And Sonoma Counties

Release date: 
Aug 17

Cotati, CA - The Marin/Sonoma Mosquito & Vector Control District (MSMVCD) announced today that four (4) more dead birds have tested positive for West Nile virus (WNv), three (3) of which were collected from Sonoma County and one (1) from Marin County. This brings the total to ten (10) WNv positive birds in Marin and Sonoma counties. 


The first indication of WNv in Marin County was found in a dead bird that was collected on August 7th near Grant Avenue in Novato.


"Two out of the four positive dead birds were classified as positive-recent, meaning they had been infected this season. This means there could be an increased risk of WNv transmission from mosquitoes to humans," said Piper Kimball, Scientific Programs Director for MSMVCD. The two dead birds that tested positive-recent were both collected on August 6th in the vicinity of Llano and Hall Roads in Santa Rosa.


Kimball said that the remaining two positive dead birds were classified as positive-chronic, including the one collected in Novato. "Dead birds classified as being positive-chronic indicate low levels of the virus and do not likely pose an increased risk of WNv transmission to humans," explained Kimball. A positive-chronic infection in a dead bird usually means the bird has been infected for quite a while, possibly even from the year prior.


Information on chronically-infected birds contributes to the understanding of the history of WNv transmission in an area and increases the knowledge of the ecology of the virus. MSMVCD continues to conduct mosquito surveillance in the areas where the birds were found. Additional information about West Nile virus in California or how to report a dead bird is available at www.westnile.ca.gov.


West Nile virus symptoms may include headache, fever, body aches, vomiting, nausea, swollen lymph glands, and skin rash on the chest, stomach and back.


Approximately 80% of people who become infected with WNv will not show any symptoms; however, approximately 20% of infected individuals however will develop West Nile fever.  

Less than 1% of those individuals who become infected may develop a more severe form of illness with symptoms such as high fever, headache, neck stiffness, disorientation, coma, paralysis and in extreme cases death. While there is no cure for WNv, it is preventable. 


Residents can help reduce the threat of WNv in the following ways:   

  • Eliminate unnecessary standing water in discarded tires, buckets, kiddie pools or any other item that can hold water for more than a week.
  • Report mosquito problems, neglected swimming pools, or any area that could be producing mosquitoes.
  • 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.
  • Wear mosquito repellent when outdoors during dusk and dawn. Use a repellent containing one of the following active ingredients: DEET, Picaridin, oil of lemon eucalyptus, or IR3535.

For more information or to report mosquito problems contact the Marin/Sonoma Mosquito & Vector Control District at 1.800.231.3236 or visit www.msmosquito.com. Report dead birds to the West Nile virus hotline at 1-877-968-2473 or online at  www.westnile.ca.gov. 


The Marin/Sonoma Mosquito & Vector Control District is an independent, special district committed to protecting public health from mosquitoes and mosquito-borne diseases. All programs and services are funded through property taxes and are provided to all residents of Marin and Sonoma counties. For more information about us please visit our website at www.msmosquito.com  or call 1-800-231-3236.