West Nile Virus
West Nile Virus (WNV) is a “new” exotic virus that has established itself in the United States and Canada over the last few years. First detected in 1999 in New York, it has spread all the way to the West Coast.
The virus is transmitted by mosquitoes from a blood meal from an infected bird. The mosquito later bites another bird, person, horse, or other animal and transmits the viral particles potentially leading to illness. WNV cannot be spread from horse to horse, or person to person. Birds are the primary carriers and seem to be the main source of virus.
Horses are the most susceptible to contracting WNV and becoming ill. There have been rare incidences in dogs and llamas. If an unvaccinated horse is exposed to the virus and becomes ill, it has a 40% chance of dying or being euthanized.
Symptoms in horses affect the nervous system and can range from stumbling, twitching, paralysis, depression, convulsions, coma, and death. Other diseases can also cause similar symptoms. If any of these symptoms are noted, call your veterinarian immediately.
There is no specific treatment for WNV. Supportive treatment may save the horses life, however prevention is the best medicine. Mosquito control and vaccinating your horse will greatly reduce the risk of infection.
A vaccine has been approved for use in horses and found to be very efficacious. According to the study, 95% of horses vaccinated with 2 doses, and later challenged with the disease, were free of infection.
In 2001, there were 738 cases of clinical WNV reported in horses in the United States. In 2002, the number had increased to 14,717. As mentioned earlier, 40% of the horses that get sick from WNV will die or be euthanized. WNV is expected to come into Utah this year and the mosquito season is not far off.
Contact your veterinarian to discuss vaccinating your horse against this deadly disease. The initial vaccination consists of 2 injections 3-6 weeks apart, then yearly boosters.
Dr. Scott Carter
Mountain View Veterinary Health Center