West Nile virus (WNV) is a potentially serious illness transmitted by mosquitoes to people. The virus survives in nature in birds and is passed when a mosquito feeds on an infected bird. The infected mosquito can then pass the virus when it bites humans and other mammals, such as horses. Most persons (80%) who become infected with the virus will not become ill. However, for the small proportion who do become sick (20%), symptoms can include fever, headache, rash, muscle weakness, nausea, and vomiting. A very small proportion (1%) may develop neurological symptoms such as limb paralysis, tremors, and altered mental status. In rare cases, WNV can be fatal.

WNV cannot be passed from person to person, only from the infected mosquito to a person. Many people who are diagnosed with WNV do not remember being bitten by a mosquito. Treatment for WNV is typically supportive care as most illnesses resolve on their own.

Before 1999, when it was detected in New York City, WNV was found in Africa, Asia, Europe, Middle East, and Australia. Since then, the virus has spread throughout the United States as well as other parts of North America. The first human cases of WNV reported in Kern County were in 2004. Since then, more than 500 cases have been diagnosed in Kern County residents.

While there is a vaccine against WNV for horses, there is no vaccine available for people. The best prevention against WNV is avoiding mosquito bites. To decrease your risk of mosquito-transmitted infections:

• Avoid mosquitoes at all times of the day.
• Avoid mosquito-infested areas and use mosquito repellent on exposed skin.
• Wear long-sleeved shirts and long pants whenever you are outdoors.
• Do not allow water to collect and stagnate in old tires, flowerpots, fountains, birdbaths, pet bowls, or other containers. These are prime breeding grounds for mosquitoes.
• Keep swimming pools operating properly; drain water from pool covers.
• Stock garden ponds with fish that eats mosquito larvae such as gambusia, goldfish, and others.
• Empty and scrub the walls of birdbaths and wading pools weekly to remove any attached mosquito eggs.
• Make sure that doors and windows have tight-fitting screens in good repair to keep mosquitoes out of your home.

Reported West Nile Virus Activity in Kern County

(updated 11/4/2024)

Reported St. Louis Encephalitis Virus Activity in Kern County

(updated 11/4/2024)

Additional Resources

• WestNile.ca.gov
• WestNile.ca.gov FAQ
• CDC - West Nile Virus
• CDC - West Nile Virus Prevention
• CDC - St. Louis Encephalitis Virus
• CDPH - St. Louis Encephalitis Virus
• CDPH - Mosquitoes and Mosquito-Borne Diseases

Mosquito Control Districts

• Kern Mosquito & Vector Control District
• West Side Mosquito and Vector Control District
• Delano Mosquito Abatement District