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July 24, 2023 - West Nile Positive Mosquito Groups Found In Newark And Fremont

The presence of West Nile virus positive mosquitoes in Fremont and Newark warrants additional caution and mosquito prevention efforts

HAYWARD, CA - To date, Alameda County Mosquito Abatement District has detected 2 dead birds and 4 groups of mosquitoes which have tested positive for West Nile virus in Alameda County. The birds were collected from Alameda and Pleasanton. The mosquitoes were collected in Fremont and Newark. Recent West Nile virus positive mosquito detections indicate heightened virus transmission potential in the Newark and Fremont areas. West Nile virus (WNV) is transmitted to people and animals through the bite of an infected mosquito. 

The district is intensifying efforts to locate and treat areas of standing water where the West Nile virus positive birds and mosquitoes were discovered. Residents will see additional staff in the areas near where the WNV mosquitoes were found, see the link for locations:

Mosquitoes need standing water to complete their life cycle. Residents are urged to be proactive by eliminating sources of water where mosquitoes can breed, and to contact the Alameda County Mosquito Abatement District if they find standing water in public or inaccessible areas. Many birds, especially crows, ravens, and songbirds are especially vulnerable to West Nile virus, and the district collects and tests deceased birds found in the county for the virus. If a resident finds a dead bird please report it by calling (877)WNV-BIRD or online at

"Infected mosquitoes in an area means there is an increased risk for West Nile virus transmission to people," says Laboratory Director Eric Haas-Stapleton. "Protect yourself and your family by applying mosquito repellent when spending time outdoors. Containers of water at homes should be dumped and drained, or tightly covered to prevent mosquitoes from breeding in your neighborhood."

Mosquitoes may breed in almost any type of standing water including but not limited to catchbasins, stormdrain systems, bird baths and swimming pools. Neglected swimming pools can be a major source of mosquito breeding throughout California, including Alameda County. If you or anyone you know has an unmaintained swimming pool please inform the District so the proper treatment can be made.

As of 7/21/2023, California has recorded West Nile virus in 113 dead birds, 827 mosquito samples, and 1 human case.  

Reduce the risk of contracting mosquito-borne diseases by following these guidelines:

  • DUMP/DRAIN standing water on your property to decrease opportunity for mosquitoes to breed.
  • DAWN/DUSK is when mosquito activity peaks, limit outdoor activities during this time.
  • DEFEND yourself from mosquito bites by wearing long pants and long-sleeved shirts and apply insect repellent containing EPA-registered active ingredients such as DEET, Picaridin, IR3535, or Oil of lemon eucalyptus.
  • DOOR/window screens should be in good condition with no tears or holes.

There is no cure for West Nile virus. Approximately one in five people who are infected with West Nile virus will develop symptoms such as fever, headache, body aches, joint pains, vomiting, or rash. Less than one percent will develop a serious neurological illness such as encephalitis or meningitis. Adults over 50 years old and people with compromised immune systems are at increased risk of serious complications. Anyone who develops symptoms should seek medical care immediately.

Horses are very susceptible to West Nile virus, however vaccines are available. Horse owners are advised to contact their veterinarians regarding timely vaccinations.

For information about mosquitoes, West Nile virus, or to request any of the District services visit or call (510) 783-7744. Residents can also request mosquitofish for their fish ponds, horse troughs, or neglected swimming pools at the District office located in Hayward at 23187 Connecticut St. For information concerning West Nile virus symptoms, prevention or testing please contact the Alameda County Public Health Department at (510) 267-8001.