Mosquitoes carrying West Nile virus were found in Atherton on Thursday, prompting the San Mateo County Mosquito and Vector Control District to schedule fogging to kill mosquitoes in parts of Atherton and Redwood City early Saturday morning.
Seven dead birds infected with West Nile virus had been found in the nearby area over a two-week period between July 6 and July 20.
"Given the number of infected birds and mosquitoes found in this area, it's very important that we act quickly," said Megan Caldwell, the district's public health education and outreach officer. "We know the virus is circulating and there is an immediate risk of human infection."
Brian Weber, the district's assistant manager, said the district is "very concerned about the risk of human West Nile virus infection in this area. Residents are strongly encouraged to avoid mosquito bites by wearing insect repellent or staying indoors around dusk and dawn."
The treatment is scheduled to take place between midnight and 5 a.m. Saturday morning, July 30. Ms. Caldwell said the treatment will be with Zenviex E4 (4% etofenprox) applied with a truck-mounted ultra-low-volume fogger at a rate of around one ounce per acre.
The treatment area is primarily residential, with approximate boundaries of Woodside Road to the west, Selby Lane to the south, Atherton Avenue to the east, and the railroad tracks to the north, the district says.
For more information or assistance with a mosquito problem, call the district at (650) 344-8592, Monday through Friday from 8 a.m. to 4:30 p.m. or visit www.smcmvcd.org.
While infected adult mosquitoes are capable of transmitting West Nile virus to humans, many of those infected show no symptoms, Ms. Caldwell said. Adults over age 50 are at higher risk of severe illness if infected.
The primary hosts of West Nile virus are birds, but humans, horses and other animals can become infected if bitten by an infected mosquito. It cannot be spread from person to person.
Precautions that can be taken to avoid mosquito bites, include:
> Keep doors and windows closed or tightly screened, and inspect screens regularly for openings.
> Wear insect repellent and/or long sleeves and pants outdoors, especially at dusk and dawn when mosquitoes are most active.
> Dump and drain standing water where mosquitoes may breed.
The district says the treatment does not pose any significant risk to humans, pets, gardens, wildlife or the environment and no special precautions are needed before or during the fogging.
District technicians are also going to be in the area this week and next working to prevent more mosquitoes from hatching, especially by finding and treating or eliminating any standing water where mosquitoes may be developing.
Mosquitoes will be collected in the area after the treatment is complete. If post-treatment mosquito samples are carrying West Nile virus, additional adult mosquito control treatments may be necessary.
Reports of dead birds are an early indication that West Nile virus is circulating in the environment. Residents may report fresh carcasses of birds or tree squirrels to the West Nile virus hotline, online at www.westnile.ca.gov or by phone at 877-WNV-BIRD (877-968-2473).