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.
California Department of Public Health (CDPH) Director and State Health Officer Dr. Karen Smith today announced the first confirmed death in California due to West Nile virus (WNV). The deceased person was a senior citizen in Sacramento County.
Dead Birds are First Indication of West Nile Virus in San Mateo County in 2016
Burlingame, CA – July 7, 2016
Two dead American crows, one collected from Atherton and another collected from Redwood City, tested positive for West Nile virus (WNV) on July 6th. This is the first indication of the presence of WNV in San Mateo County in 2016.
In 2015 to date, 16 dead birds and five mosquito samples have tested positive for West Nile Virus. No sentinel chickens or humans have tested positive for West Nile virus in San Mateo County this year.
In 2014, 20 dead birds and 15 mosquito samples in San Mateo County tested positive for West Nile virus. No sentinel chickens or humans tested positive in 2014.
This table compares the MIR (minimum infection rate) of mosquito samples collected in San Mateo County in 2014 and 2015, This number is a measure of what proportion of our mosquito population (per 1000) is carrying West Nile virus.
This table compares the number of bird and mosquito samples testing positive for West Nile virus this year compared with this time last year.
This map shows the location of all bird and mosquito samples testing positive for West Nile virus so far in 2015.
Mapping the location of these results helps our laboratory staff better understand the patterns of disease transmission between birds and mosquitoes in our county. The presence of cluster of positive bird and mosquito samples is one of the clues that tells us that West Nile virus is being transmitted locally – and that humans are at risk for infection.
The attached map shows the location of all dead birds tested for West Nile virus in 2015. The red bird-shaped icons are tested birds (not all reported birds are in testable condition), while the large green and red icons are this years’ West Nile virus positive birds.