After fogging mosquitoes in one Atherton neighborhood over the weekend, additional adult mosquitoes carrying West Nile virus have been found in Atherton, prompting the scheduling of more fogging Thursday night.
The San Mateo County Mosquito and Vector Control District announced the find Aug. 3 and said the fogging would take place from 9 p.m. Thursday, Aug. 4, to 5 a.m. Friday, Aug. 5.
The newly discovered disease-carrying mosquitoes were collected in the vicinity of Selby Lane and Stockbridge Avenue, following an adult mosquito fogging in a neighboring area in the early morning on July 30, the district said.
"Mosquitoes collected from last week's treatment area were clear," said Megan Caldwell, the district's education and outreach officer, "but we found infected mosquitoes in another area nearby. We're very concerned about the risk of West Nile in this area."
Caldwell urged local residents take precautions to avoid mosquito bites.
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, prompting the initial testing of mosquitoes.
Ms. Caldwell said the treatment will be with Zenviex E4 (4 percent 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 Selby Lane, Montgomery Avenue and Hull Avenue on the north, Alameda de las Pulgas on the west, Camino al Lago, Faxon Road and Atherton Avenue on the south and Austin Avenue and Elena Avenue on the east.
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 smcvdc.org.
While infected adult mosquitoes are capable of transmitting West Nile virus to humans, many people who are 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 working to prevent more mosquitoes from hatching, especially by finding and treating or eliminating any standing water where mosquitoes may be developing.
Mosquitoes will again 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 on westnile.ca.gov or by calling 877-WNV-BIRD (877-968-2473).