Contra Costa Mosquito & Vector Control

FOR IMMEDIATE RELEASE     -     September 19, 2014

Contact: Deborah Bass
               Public Affairs Mgr.

(925) 771-6112 - office
(925) 260-4670 - mobile 

For human cases, please contact Contra Costa Health Services at 888-959-9911


Pasture mosquitoes aggressive, not known to transmit West Nile virus 


CONCORD, CALIFORNIA - - The Contra Costa Mosquito & Vector Control District is targeting two types of mosquitoes in the eastern part of Contra Costa County. The first, a Culex mosquito, thrives in permanent or residential water sources and can transmit West Nile virus. The second, an Aedes mosquito, commonly known as a pasture mosquito, thrives in intermittent water sources such as coastal marshes and agricultural areas. The Aedes is not known to transmit the virus. The mosquitoes are just two types of 23 that inhabit Contra Costa County.


"Although the pasture mosquito is an extremely aggressive biter, it is not known to be a vector, a transmitter, of West Nile virus," said Steve Schutz, Ph.D, scientific program manager for the District. "East county is home to duck clubs, agricultural areas, farms and ranches -- it's a very challenging area to maintain in terms of mosquito production where flooding occurs intermittently and often to us, unexpectedly. We are working to locate and treat the sources of mosquitoes as quickly as possible and fogging for adult mosquitoes when the number of mosquitoes trapped exceed thresholds."

The District reports today that a group of mosquitoes from Discovery Bay tested positive for West Nile virus as well as one bird from San Ramon. All 2014 West Nile virus activity can be found on the District's website.

According to the California West Nile Virus website, so far this year there are 311 human cases compared to 150 last year, 2079 dead birds compared to 1067 last year, and 2853 mosquito samples compared to 2173 last year. Infected mosquitoes can infect people with the virus in just a single bite.


Residents are urged to help reduce their risk of contracting mosquito-borne diseases by following these guidelines: 

  • Dump or drain standing water. Mosquitoes can't begin their lives without water.
  • Defend yourself against mosquitoes by using repellents containing DEET, Picaridin, or Oil of Lemon Eucalyptus.
  • Avoid being outdoors when mosquitoes are present, typically dawn and dusk.
  • Report neglected swimming pools by calling 925-771-6195 or visiting  Anonymous calls accepted. Just one neglected pool can produce more than 1 million mosquitoes and affect people up to five miles away. 
  • Report dead birds to the state hotline: 1-877-968-2473. All reports are crucial, even if the bird does not meet criteria for testing.

Since 2005, 48 people in Contra Costa County have been diagnosed with West Nile virus. In 2006, two people died from the disease. Recent studies have shown that the majority of cases are not diagnosed and are grossly underreported. For 2014, a total of 21 groups of mosquitoes, 13 chickens and 39 dead birds have tested positive for the virus.  


Visit the District's website or click on these links for current West Nile virus activity  or to receive automatic emails for when the District fogs for adult mosquitoes.


Contra Costa Mosquito & Vector Control District, an independent special district and public health agency, is located at 155 Mason Circle in Concord. Call the District to report mosquito problems at (925) 771-6195 or visit their office between 8:00 a.m. and 4:30 p.m. to get FREE mosquitofish for ornamental ponds, horse troughs or neglected swimming pools.    


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