West Nile Virus found in Martinez

A group of mosquitoes trapped in Martinez on March 27 have tested positive for West Nile virus, the first virus-positive group in Contra Costa County this year.

Scientists at the Contra Costa Mosquito and Vector Control District cited warm winter weather as a possible cause discovering infected insects nine weeks earlier than the first positive mosquitoes last year, and for the first time ever, before infected birds have been found.

“The first virus-positive group of mosquitoes is significant,” said Deborah Bass, spokeswoman for the District. “It means that mosquitoes have the virus and are capable of infecting anyone of any age, at any time. Wearing mosquito repellent and maintaining or dumping outdoor water sources remain the best precautions people can take. Residents can also continue to report dead birds to the hotline which remain crucial to our surveillance and control efforts.”

One of the suspected mechanisms for the re-introduction of West Nile virus each year is that infected female mosquitoes ‘hibernate’ over the winter and emerge the next season to start the cycle again.

One reason for the infected mosquitoes to emerge so early this year could be due to the unusual warm weather experienced in January when temperatures reached nearly 80 degrees. 

Since the arrival of West Nile virus in Contra Costa County in 2004, 27 people have been documented with the disease and two have died. Most people who are bitten by a mosquito with WNV will not get sick; however, up to 20 percent of the population infected with WNV will get West Nile fever. West Nile fever causes people to experience mild to severe flu-like symptoms such as fever, headache, body ache and possible paralysis. Less than one percent of infected individuals will require hospitalization. The elderly and those with compromised immune systems are most susceptible to illness and death caused by WNV.

Residents are urged to take precautions such as defending against mosquitoes by using a repellent with an effective active ingredient such as DEET, Picaridin or Oil of Lemon Eucalyptus; draining all sources of standing water that may support mosquito-breeding habitats, as residential sources can be a big producer of mosquitoes in Contra Costa County; properly sealing all door and window screens; vaccinating horses as horses are highly susceptible to West Nile virus—approximately half of the horses that get WNV die or have to be euthanized; dressing appropriately by wearing long sleeves and pants when outdoors and mosquitoes are present; and reporting all dead birds to the California Department of Public Health’s Dead Bird Hotline at 877-WNV-BIRD (877-968-2473) or on their Web site http://www.westnile.ca.gov/.

Not all birds will be picked up and tested, but reporting dead birds provides crucial information for mosquito control efforts. To learn if the District is spraying for adult mosquitoes in Contra Costa County, please visit the district’s Web site at www.ccmvcd.dst.ca.us or call the District at (925) 771-6195 for a recorded message.