Mosquitoes Infected with West Nile Virus Detected in Cloverdale

Release date: 
Sep 12

Cotati, CA-The Marin/Sonoma Mosquito & Vector Control District (MSMVCD) has confirmed its first West Nile virus (WNV) positive mosquito sample for 2013. The mosquitoes were collected from Cloverdale, in the vicinity of Citrus Fair Drive and Asti Road. This is near the area where a sentinel chicken tested positive for WNV antibodies last month.

“This is a reminder that WNV continues to be a health threat in Sonoma and Marin counties,” stated Nizza Sequeira, Public Relations Director for the Marin/Sonoma Mosquito and Vector Control District. “We anticipate more activity as we enter the late summer months, when temperatures generally spike.”

Historically, late September and October is when WNV activity in the mosquito population increases. 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 faster.

MSMVCD staff continues to trap, test and monitor the abundance of adult mosquitoes in the area. Current lab surveillance data has shown a decrease in the adult mosquito population over the past week. Vector control technicians are inspecting the area for new sources of mosquito production as well as checking all existing sources.

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:

  • 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 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

  • 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 (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.


The Marin/Sonoma Mosquito and Vector Control District is an independent special district committed to protecting public health from mosquitoes and vector-borne disease. All programs and services are funded through benefit assessments and property taxes. Services are provided to all residents in Marin and Sonoma counties.