The District’s West Nile virus surveillance program reports several types of positive West Nile virus results, including dead birds, mosquito samples (“pools”), sentinel chickens, and human cases.
For more information about the District’s West Nile virus and mosquito population surveillance, visit the Mosquito Surveillance page.
On April 2nd, a dead American crow collected in South San Francisco tested positive for West Nile virus. This is the second dead bird positive for West Nile virus found in San Mateo County in 2018. The first was collected in February in Foster City.
On April 2nd, a dead American crow collected in South San Francisco tested positive for West Nile virus. This is the second dead bird positive for West Nile virus found in San Mateo County in 2018. The first was collected in February in Foster City.
Follow-up mosquito trapping in the area where the bird was found did NOT detect any mosquitoes infected with WNV.
On Feb. 5th, a dead American crow collected in Foster City tested positive for West Nile virus. This is the first sign of the virus in San Mateo County in 2018.
The West Nile Virus season has wrapped up for the year, with the final chicken bleeding on October 30. Although one bird tested positive in January, the District did not detect any evidence of West Nile Virus (WNV), Saint Louis encephalitis, or Western Equine encephalitis in San Mateo County during the active summer season. The surveillance efforts are summarized below:
As of September 28, 2017, there have been 320 dead birds reported in San Mateo County. Of those, 56 have been suitable for testing and 1 has tested positive (2%) for West Nile Virus (WNV). Nine dead squirrels and four mosquito pools have been tested for West Nile Virus in San Mateo County thus far this year, and none of them have tested positive.
As of August 25, 2017, there have been 286 dead birds reported in San Mateo County. Of those, 52 have been suitable for testing and 1 has tested positive (2%) for West Nile Virus (WNV). No dead squirrels or mosquito pools have been tested for West Nile Virus in San Mateo County thus far this year.
As of June 630, 2017, there have been 215 dead birds reported in San Mateo County. Of those, 45 have been suitable for testing and 1 has tested positive (2%) for West Nile Virus (WNV). No dead squirrels or mosquito pools have been tested for West Nile Virus in San Mateo County thus far this year.
As of June 6, 2017, there have been 134 dead birds reported in San Mateo County. Of those, 21 have been suitable for testing and 1 has tested positive (5%) for West Nile Virus (WNV). No dead squirrels or mosquito pools have been tested for West Nile Virus in San Mateo County thus far this year.
As of April 28, 2017, there have been 56 dead birds reported in San Mateo County. Of those, 15 have been suitable for testing and 1 has tested positive (7%) for West Nile Virus (WNV). No dead squirrels or mosquito pools have been tested for West Nile Virus in San Mateo County thus far this year.
It is unusual to detect West Nile Virus in dead birds during the winter months. West Nile Virus season begins mid-April, with most activity in the summer. However, residents can report some species of dead birds (crows, ravens, scrub-jays, finches, sparrows, hawks and owls) year-round online at westnile.ca.gov and the District laboratory will test fresh specimens without signs of trauma (roadkill or partially decomposed specimens cannot be tested).The first West Nile Virus positive bird of 2017 in San Mateo County was detected in Redwood City.
The West Nile Virus Dead Bird Hotline, operated by the California Department of Public Health (CDPH), will not be answered by live operators after October 14, 2016 until next spring. However, residents can still call the phone number 1-877-WNV-BIRD and leave a message or fill out an online form at westnile.ca.gov to report dead birds. During the winter season, the District will continue to collect and test suitable birds of the following groups: corvids, finches, sparrows, owls, and hawks.
The California Department of Public Health generates a risk assessment level ranging from 1-5 for West Nile Virus (WNV). The risk level is determined by analyzing a combination of data on mosquitoes and infection rates gathered by the District, weather patterns and the state WNV hotline. The risk levels are explained as:
Risk Rating 1.0—2.5 Normal Season, “No Alert Level”
Mosquito samples collected from Atherton following San Mateo County Mosquito and Vector Control District’s adult mosquito control treatment on Thursday, Aug. 4th, have tested negative for West Nile virus.
“Although we didn’t find infected adult mosquitoes this week, residents are encouraged to continue to take basic precautions against mosquito bites,” said the District’s Public Health Education and Outreach Officer, Megan Caldwell.
