In this month's District Report: 2016 West Nile Virus Update
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2016 West Nile Virus Season Update
2015 was California's deadliest year ever for West Nile virus: there were 585 cases of neuroinvasive disease and 53 fatalities. During the 2015 West Nile virus season, 23 dead birds and 5 mosquito samples collected from San Mateo County tested positive for West Nile virus.

So how will year's West Nile virus season stack up against 2015? Laboratory Director Dr. Nayer Zahiri says it's too soon to say.

So far this year, the District has detected West Nile virus in a total nine bird carcasses. Comparison to previous years (graph below) suggests that more birds will be found as the WNV season progresses, but only time will tell.

Year-to-date comparison of WNV-positive bird specimens, 2014-2016
However, mosquitoes carrying West Nile virus are the real public health threat. Although 2015 was the deadliest WNV season on record for California, it was a mild WNV season for San Mateo County, with only five mosquito samples testing positive for WNV all summer. This year, there have already been five mosquito samples positive for West Nile virus (graph below)

Year-to-date comparison of WNV-positive mosquito specimens, 2014-2016
Although no new mosquito samples have tested positive for West Nile virus this week, there is still more than a month left in this year's West Nile virus season. If the previous years are any indication, we're likely to see more West Nile virus in San Mateo County this year.
The latest information on West Nile virus in San Mateo County is always available at
Reduce Your Risk of West Nile Virus

Avoiding mosquito bites is easy with the '3 Ds':

1. Dump & drain standing water around your home so mosquitoes can't breed.

2. Dusk & dawn are when the mosquitoes that transmit WNV are active. Wear repellent, stay covered up, or stay indoors.

3. DEET, IR-3535, picaridin, or oil of lemon eucalyptus are effective at repelling mosquitoes. Look for repellentes that contain these active ingredients.

For more tips, visit the District website.
Sentinel Chickens Hard at Work

These 30 seasonal employees get paid chicken feed, but they have a very important job: they're part of the District's West Nile Virus surveillance program.

Each sentinel chicken gives a biweekly blood sample for West Nile virus testing. Since the chickens never leave their coop, any that are infected signal the presence of WNV in that area.

Learn more on the District website.
Reporting Dead Birds for West Nile Virus Testing

What: Dead birds or tree squirrels that apear to have been dead less than 24 hours
When: Anytime!
How: Call 877-WNV-BIRD or visit
Why: Dead birds are often the first indication that WNV is circulating in an area
San Mateo County Mosquito and Vector Control District
Protecting public health since 1916

1351 Rollins Rd. | Burlingame CA 94041
(650) 344—8592 |

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San Mateo County Mosquito and Vector Control District · 1351 Rollins Rd. · Burlingame, CA 94010 · USA

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