First Sign of West Nile Virus Hits Sonoma County

Release date: 
May 15

Cotati, CA.-The Marin/Sonoma Mosquito & Vector Control District (MSMVCD) has confirmed its first West Nile virus (WNv) positive mosquito sample for 2014. The mosquitoes were collected from Sonoma, in the vicinity of Ramal Road and Poehlman Rd. This is the earliest that the virus has been detected in the local mosquito population since 2008.

Mosquito control operations have been conducted to decrease the abundance of adult and larval mosquitoes and to break the transmission cycle. District staff will continue to trap, test, and monitor the abundance of adult mosquitoes in the area and perform control operations as necessary. Vector control technicians are inspecting the area for unknown sources of mosquito production as well as checking all existing sources.

"Our season began much earlier this year, both in terms of mosquito abundance and virus detection," stated Nizza Sequeira, Public Relations Director for the District. "While we cannot predict the amount of West Nile virus activity that may occur in a given year, we do see the potential for a higher level of virus activity than in past years," stated Sequeira.

The rise in the average daily temperature speeds up the mosquito life cycle, shortening the development time from egg to adult to as little as five days. The heat also causes the amplification of the virus in infected mosquitoes, allowing the virus to spread easier and more quickly.

Residents are urged to continue to report mosquito problems in their area 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:

  • Cover rain barrels and other containers with a mosquito-proof screen (fine mesh-1/16 of an inch).
  • Check septic tank lids to ensure a tight seal, repair cracks and screen vent pipes using a fine mesh screen (1/16 of an inch).
  • Report mosquito problems, neglected swimming pools, or any area that could be producing mosquitoes at or 1-800-231-3236.
  • Stock backyard ponds or other permanent water features with mosquitofish.
  • Report dead birds to the West Nile virus hotline at 1-877-968-2473 or online at
  • 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.

Historical data regarding human cases of WNv have shown that less than 1% of people (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.