West Nile virus is one of the fastest growing health threats to U.S. horses today.  Since its discovery in New York in 1999, this mosquito-borne disease has spread quickly throughout the country.

The cycle starts with infected birds, which can travel long distances in a short period of time.  When a mosquito feeds on a bird carrying the West Nile virus, it too becomes infected.  The mosquito then feeds on a horse, human or other mammal. Once a horse has been bitten, it may take 5 to 15 days for signs of West Nile virus to appear.

West Nile virus concerns equine veterinarians because it can cause Encephalitis, which is swelling of the brain and spinal cord.  Infected horses can suffer muscle weakness, partial paralysis, fever, convulsions, coma and death.  Once horses show clinical signs of illness, the disease is fatal nearly 40% of the time.  There is no evidence that horses can transmit West Nile virus to other horses, birds, or people.

After the initial vaccine, a booster is required 3 to 5 weeks later.  To date we have not seen nor heard of any reactions to this vaccine.  This new vaccine has shown that vaccinated horses develop serum-neutralizing antibodies against West Nile virus, which helps to protect the horse from the disease.  We suggest vaccinating your horses as soon as possible.

You may obtain more information on the West Nile virus at http://westnile.ca.gov/

You may also contact us here at the clinic.