West Nile Activity Continues as More Mosquitoes Test Positive in East Contra Costa

Press Release


The District Urges Citizens to Protect Themselves and Their Horses From WNV

CONCORD, CA – The Contra Costa Mosquito & Vector Control District is reporting mosquitoes from Brentwood, Discovery Bay and Byron have tested positive for West Nile virus. This is the first West Nile virus activity of the year in Byron.

So far this year, 13 groups of mosquitoes, eight dead birds, and 13 chickens from Contra Costa County have tested positive for the virus.

According to the District’s Scientific Programs Manager Steve Schutz, Ph.D., “This time of the year typically marks the peak of West Nile virus season, and so it is very important that citizens prevent mosquito bites by wearing repellent and horse owners should make sure their horses have had the recommended vaccinations to reduce the risk of equine cases of West Nile virus.”

Horses are susceptible to West Nile virus. The American Association of Equine Practitioners recommends horse owners consult their veterinarian about the equine vaccination to prevent West Nile virus. Unvaccinated horses can become infected by a mosquito bite and experience fever, paralysis, seizures and neurological symptoms. Since 2003, there have been more than 1,200 equine West Nile virus cases statewide; 534 infected horses have died or had to be euthanized.

To prevent mosquito bites, Contra Costa County residents should:

  • Wear mosquito repellent when outside. Repellents containing DEET, Picaridin, or Oil of Lemon Eucalyptus are most effective and are recommended by the Centers for Disease Control and Prevention (CDC).
  • Stay indoors when mosquitoes can be present. Mosquitoes that can transmit West Nile virus are active at dawn and dusk.

To further reduce the risk of contracting West Nile virus and other mosquito-borne diseases:

  • Dump or drain standing water to prevent mosquitoes. Most mosquitoes can’t start their lives without water.
  • 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: 12

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

Dead Birds: 8

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

Sentinel Chicken Flocks: 2

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

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.