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Protecting Yourself and Your Pets from West Nile Virus

Welcome to our latest newsletter, where we aim to keep you informed about West Nile virus (WNV) and how to protect yourself and your pets. West Nile virus remains a serious concern, not just in Marin and Sonoma counties,  but nationwide. Here’s how this virus is transmitted and some ways to safeguard against it.

 How is WNV is transmitted?

Most often, WNV is spread by the bite of an infected mosquito. Mosquitoes are WNV carriers ("vectors") that become infected when they feed on infected birds. Infected mosquitoes can then spread WNV to humans and other animals when they bite them.

What are the symptoms of WNV?

Approximately 80% of infected individuals (4 out of 5) experience no symptoms and are often unaware of their WNV infection. Around 20% of those infected (1 out of 5) may exhibit mild symptoms, such as fever, headache, body aches, nausea, vomiting, and sometimes a skin rash. These symptoms typically emerge 3 to 14 days after a mosquito bite and usually resolve within a few days, although fatigue and weakness can persist for weeks or months.

In rare cases, less than 1% of individuals (around 1 out of 150) may develop severe illness. West Nile virus can affect the brain and/or the nervous system, leading to conditions like encephalitis (brain inflammation) or meningitis (infection of the brain or its surrounding tissue). These severe symptoms may include high fever, headache, neck stiffness, vision impairment, numbness, confusion, muscle weakness, paralysis, and even coma. Such symptoms can endure for several weeks, and the impact on the nervous system may be long-lasting. In very severe cases, WNV can be fatal.

People over the age of 60 and individuals with compromised immune systems are at greatest risk of becoming ill and are more likely to develop serious symptoms when infected with WNV.

Can pets get WNV?

Dogs and cats can get WNV from the bite of an infected mosquito, but it is rare for pets to get sick.

Horses can also get WNV from the bite of an infected mosquito, which can lead to severe disease and even death. Signs of WNV in horses may include stumbling, hind leg weakness, inability to stand, drooping lips, sensitivity to touch or sound, muscle tremors, and death. Horse owners should talk to a veterinarian about the WNV vaccine for horses.

Protecting Yourself, Your Family, and Your Pets

  • Use Mosquito Repellent: Apply an EPA-registered mosquito repellent on exposed skin containing one of these active ingredients, DEET, Picaridin, oil of lemon eucalyptus or IR3535.
  • Wear Protective Clothing:  Wear long-sleeved shirts and pants when outdoors, especially during dusk and dawn when mosquitoes are most active.
  • Eliminate Standing Water: Mosquitoes reproduce in standing water, so empty containers such as flower pots, bird baths, and ponds to reduce mosquito breeding sites.
  • Install Screens: Keep doors and windows screened to prevent mosquitoes from entering your home.
  • Report Mosquito Problems: Contact the Marin/Sonoma Mosquito & Vector Control District (707-285-2200) if you have a mosquito-related problem that you cannot resolve on your own.
  • Consult Your Veterinarian: Talk to your veterinarian about a West Nile Virus vaccination for your horses.

Current Statistics in California

As of the latest update, 806 dead birds and 4,305 mosquito samples have tested positive for West Nile virus in 2023, demonstrating the virus's local persistence in California. Additionally, 244 humans and 27 horses have tested positive for the virus.

By staying informed and taking necessary precautions, you can protect yourself, your family, and your pets from West Nile virus. Together, we can reduce the risk of WNV transmission in our community.

For more information about mosquitoes and mosquito-borne diseases, visit

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