Dead birds tested positive for West Nile virus in San Carlos and San Ramon this week, the first confirmed case in San Mateo County this year and the third ever in Contra Costa County.

The first Peninsula case of 2014 was discovered June 4th near San Carlos Ave at Chestnut and Cedar Street, said Robert Gay, District Manager of the San Mateo County Mosquito and Vector Control District. The third infected bird in Contra Costa County was found near Norris Canyon Road and Bollinger Canyon Road, not far from where the last infected bird in San Ramon was discovered in September 2012.

In San Mateo County, 64 birds and 16 squirrels tested positive for the virus between 2004 and 2013, Gay said. A total of 47 people have contracted the disease since 2005 in Contra Costa County, and two of them have died.

"We should all assume that West Nile virus is active everywhere in the county," said the Contra Costa district's Public Affairs Manager Deborah Bass. "Take the appropriate precautions. It only takes one mosquito bite from an infected mosquito to get the disease."

The West Nile virus is transmitted through the bite of an infected mosquito and cannot be spread from person to person, Gay said. Birds are the main hosts for the infection, but it can also infect humans, horses and other animals.

Bass noted that while the two species of mosquitoes in Contra Costa County prefer to feed on birds, they also pick up the disease from already-infected birds and can pass it onto people.


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"West Nile virus activity may increase as we head into the summer months, and it is important for residents to protect themselves from mosquito bites," said Gay, who advises residents to eliminate all sources of standing water, including flowerpots, rain gutters and pet bowls where the insects breed. "Our vector control technicians are continuously inspecting standing water and treating sources of mosquito breeding throughout the county."

West Nile symptoms in their mildest form include fever, headache, fatigue, body aches and swollen lymph glands, and can last anywhere from a few days to several weeks. In its most severe form, the virus can be fatal.

The districts advise residents to fit their doors and windows with tight-fitting insect screens and to wear insect repellent and proper clothing during dawn and dusk. Both districts will be setting mosquito traps near where the dead birds were found to collect adult mosquitoes for West Nile virus testing.

Contact Erin Ivie at eivie@bayareanewsgroup.com. Follow her at Twitter.com/erin_ivie.