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End of Season West Nile Virus Update
October 2018

San Mateo County

 

West Nile virus (WNV) season comes to an end during the month of October, when nighttime temperatures drop substantially. This year we detected WNV in five birds (all American Crows) and two mosquito pools (both Culex tarsalis) in San Mateo County. Two of the birds were collected off-season, earlier in the year than we expect disease to be circulating in the local mosquito populations. This was an increase in WNV activity compared to 2017, during which WNV was detected in one bird during the cool season.  There were no detections of WNV in mosquitoes in 2017. However, activity in 2018 was is relatively low compared to peak WNV activity in 2014.  At that time, virus was detected in 20 birds and 15 mosquito pools. WNV activity (or WNV detections) for 2018 are summarized in the tables below.

No sentinel chickens tested positive for WNV in 2018. Chicken blood will be tested a final time the first week of November, and then the chickens will be retired to a residence in the Central Valley. There were no human cases of WNV reported in in San Mateo County in 2018.

Although the state WNV hotline is closed for the year, the District asks residents to continue to report dead birds by calling 877-WNV-BIRD (968-2473). Although there will not be live operators, recorded messages with a brief description of the bird and location information will be forwarded to the District. Reports can also be made online at http://westnile.ca.gov. The District tests suitable birds on a limited basis during the winter season.

SEASONAL TOTALS OF WNV POSITIVE BIRDS – 2018

 

 

STREET

CITY

ZIP CODE

BIRD SPECIES

SUBMISSION DATE

Shell Blvd

Foster City

94404

American Crow

February 5, 2018

Sonora Ave.

South San Francisco

94080

American Crow

April 2, 2018

Seminary Dr.

Menlo Park

94025

American Crow

August 9, 2018

E. Bayshore Rd.

East Palo Alto

94303

American Crow

August 22, 2018

Gilbert Ave.

Menlo Park

94025

American Crow

August 28, 2018

 

 

SEASONAL TOTALS OF WNV POSITIVE MOSQUITO POOLS – 2018

ADDRESS

CITY

ZIP CODE

DATE

SPECIES

Wisteria Dr.

East Palo Alto

94303

August 8, 2018

Culex tarsalis

Camellia Dr.

East Palo Alto

94303

August 10, 2018

Culex tarsalis

 California

WNV has been detected in 40 counties in 2018 (see map) compared to a five year average of 40 counties at this date. Throughout California, there have been 114 human cases of WNV, including five fatalities, compared to a five-year average of 277 human cases at this date. Statewide, 6,918 dead birds have been reported and 1,849 have been tested with 469 positive results (25%). 1,889 mosquito pools have tested positive for WNV this year and 139 sentinel chickens have tested positive compared to a five-year average of 2,974 positive mosquito pools and 332 positive sentinel chickens. Overall, this is a lower than average year for West Nile Virus across the state, with the highest amount of activity in Sacramento and San Joaquin counties in the central valley.

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