West Nile Virus Persists: More Mosquitoes, A Bird, Chickens Test Positive

Press Release

Photo provided by Contra Costa Mosquito Vector Control

Concord, CA – The Contra Costa Mosquito & Vector Control District is reporting mosquitoes from Quimby Island and Bethel Island, a dead bird from Oakley, and chickens from Martinez and Oakley have tested positive for West Nile virus. This is the first West Nile virus activity from Bethel Island this year.

So far in 2018, 17 groups of mosquitoes, 12 dead birds, and 15 chickens from Contra Costa County have tested positive for the virus.

According to the District’s Scientific Programs Manager Steve Schutz, Ph.D., “Even though today is technically the last day of summer, there is warm weather in the forecast which means West Nile virus season is not over. West Nile virus replicates faster in warm weather, so county residents should continue to dump standing water to prevent mosquitoes and wear repellent to prevent mosquito bites.”

The Centers for Disease Control and Prevention (CDC) recommend repellents containing DEET, Picaridin, or Oil of Lemon Eucalyptus. Residents can also avoid mosquito bites by  staying indoors when mosquitoes can be present. Mosquitoes that can transmit West Nile virus are most active at dawn and dusk.

Most mosquitoes can’t start their lives without water, and so dumping out standing water prevents mosquitoes from having a place to develop.

And report dead birds to the state hotline: 1-877-968-2473. Birds are often the first sign of disease transmission in a particular area. Ravens, jays, crows, and magpies can be susceptible to the virus, and may die if infected. Even if the birds are not tested, the reports alone yield crucial information to protect public health.

For a list of Contra Costa County’s 2018 West Nile virus activity and locations, visit the District’s website.


Mosquito Samples: 17

n Date Reported City Cross Streets Species
1 7/11/18 Discovery Bay Cherry Hills Drive x Hwy 4 Culex pipiens
2 7/16/18

Agricultural Area East of Brentwood

Orwood Road x Levee Road Culex tarsalis
3 7/30/18 Discovery Bay Marina Rd x Willow Lake Rd Culex pipiens
4 8/1//18 Oakley E. Summer Lake Dr x Cypress Rd Culex tarsalis
5 8/8/18 Discovery Bay Willow Lake Rd x Discovery Bay Blvd Culex pipiens
6 8/13/18 Holland Tract Area Holland Tract Culex tarsalis
7 8/13/18 Martinez Waterfront Rd Mococo Rd Culex tarsalis
8 8/9/18 Oakley Blue Lake Ct x Clear Lake Dr Culex pipiens
9 8/15/18 Discovery Bay Bixler Rd x Point of Timber Rd Culex tarsalis
10 8/15/18 Quimby Island Quimby Island Culex tarsalis
11 8/20/18 Discovery Bay Cherry Hills Dr. x Hwy 4 Culex pipiens
12 8/20/18 Byron Rankin Rd x Western Farms Ranch Rd Culex tarsalis
13 8/22/18 Brentwood Fertado Ln x Ellisa Ln. Culex pipiens
14 8/29/18 Quimby Island Quimby Island Culex tarsalis
15 8/29/18 Brentwood Eden Plains Rd x Arabian Ln Culex pipiens
16 9/11/18 Quimby Island Quimby Island Culex tarsalis
17 9/17/18 Bethel Island Stone Rd Culex tarsalis

Dead Birds: 12

n Date Reported City Cross Streets Species
1 7/29/18 Brentwood Sycamore Ave x Garin Pky California Scrub-Jay
2 8/5/18 Discovery Bay Discovery Bay Blvd x Willow Lake Rd California Scrub-Jay
3 8/5/18 Discovery Bay Dune Point Wy x Dune Point Pl California Scrub-Jay
4 8/8/18 Brentwood Walnut Blvd x Carnegie Ln American Crow
5 8/15/18 Brentwood Fertado Ln x Ellisa Ln American Crow
6 8/15/18 Discovery Bay Wayfarer Dr x Cherry Hills Dr American Crow
7 8/15/18 Antioch Valley Wy x Ridgeview Dr American Crow
8 8/15/18 Concord Concord Blvd x Crestwood Cir California Scrub Jay
9 8/28/18 Martinez Blum Rd x Alan Wy California Scrub Jay
10 8/29/18 Discovery Bay Westport Cir x N Lakefront Loop American Crow
11 8/30/18 Discovery Bay Greenfield Wy x Greenfield Ct American Crow
12 9/12/18 Oakley Main St x Norcross Ln American Crow

Sentinel Chicken Flocks: 3

Note: Chickens do not die from West Nile virus. They develop antibodies to the virus which is detected in their blood.

#/10 Date Bleed Area
7 7/2/18 Holland Tract
3 7/16/18 Martinez
3 8/13/18 Holland Tract
1 9/10/18 Martinez
1 9/10/18 Oakley

Horses: 0

n Date Reported City Dead/Euthanized



Since 2005, 63 Contra Costa County residents have been diagnosed with West Nile virus. In 2006, two people died from the disease. For current human case information, please contact Contra Costa Health Services at 888-959-9911.

Contra Costa Mosquito & Vector Control District, an independent special district and public health agency, is located at 155 Mason Circle in Concord. Contact the District to report mosquito problems online or at (925) 685-9301. Visit the office between 8:00 a.m. and 4:30 p.m. to get FREE mosquitofish for ornamental ponds, horse troughs or neglected swimming pools.