A second gray squirrel tested positive for low levels of West Nile virus (WNV) in Menlo Park, according to the county.
The squirrel, captured on Aug. 2, carried a chronic level of virus as did one trapped in July, the San Mateo County Mosquito and Vector Control District said. However, mosquitoes trapped within the city during July tested negative for the virus, leaving district officials uncertain about the level of immediate risk.
"As it is, I am not sure what all these chronic positive (West Nile virus) animals really mean," said Angie Nakano, acting district laboratory director. "Just about every county in California is seeing more of them this year, and the reason why is unclear. We are using the chronic-positive information to intensify monitoring for acute virus risk, but so far have not found any."
She said that mosquitoes from all other areas with chronic-positive samples were collected and sent to the state labs at U.C. Davis, with the exception of Woodside, where not enough mosquitoes were trapped to warrant testing. The district expects test results later this week.
County cases in 2012 to date:
■ Red-shouldered hawk picked up June 11 in Woodside (WNV-positive)
■ Eastern gray squirrel picked up July 3 in Menlo Park (WNV-chronic)
■ Lesser goldfinch picked up July 22 in Redwood City (WNV-chronic)
■ House sparrow picked up July 31 in Atherton (WNV-chronic)
■ Canada goose picked up July 31 in San Mateo (WNV-chronic)
■ American crow picked up Aug. 2 in Atherton (WNV-chronic)
■ Eastern gray squirrel picked up Aug. 2 in Menlo Park (WNV-chronic)
West Nile virus is transmitted through bites from infected mosquitoes. It causes a range of symptoms, from a severe illness with nervous system malfunctions to a flu-like illness with high fever and excessive sleep, or possibly no signs of illness at all, according to the mosquito district. The district suggests limiting mosquito bites by eliminating standing water, staying covered or indoors during dawn and dusk, and wearing mosquito repellent.
Residents can call 344-8592 for help with a mosquito problem. The agency asks residents to report dead birds or tree squirrels either online at westnile.ca.gov or by calling 877-968-2473.
More information about the virus can be found here.