What is Western Equine Encephalitis?

Western Equine Encephalitis is a virus transmitted through the bite of an infected mosquito. The transmission cycle is between wild birds and mosquitoes. A mosquito will bite a bird infected with Western Equine Encephalitis and become infected. While looking for another blood meal, an infected mosquito can infect an uninfected bird, horse, or human. In past outbreaks, this disease has caused severe illness and death in horses.

What are the signs and symptoms of Western Equine Encephalitis?

• No Symptoms: Most of those infected with Western Equine Encephalitis will have no symptoms or signs and never feel sick
• Mild Symptoms: Most of those who do have symptoms or signs will have a fever and headaches
• Severe Symptoms: Few of those infected have the severe symptoms, the old and the young. These include high fever, stiff neck, vomiting, lethargy, disorientation, seizures, and possible death

Is Western Equine Encephalitis seasonal?

Yes, it is most likely to occur in late spring to early summer.

Is Western Equine Encephalitis in San Mateo County?

Western Equine Encephalitis is sometimes detected in mosquito pools and sentinel chickens in Southern California but has not been found in San Mateo County recently.