Dr. Glen Jensen of Emery Animal Health vaccinates a horse against the West Niles Virus. While the West Niles Virus has not been found in Utah many local horse owners have chosen to vaccinate their horses just in case. In the past couple of years the virus has been found to make some geographical leaps later in the season. The virus spreads from birds to mosquitos, not from horse to horse and their is no fear of the virus spreading during the winter months. While it has been found in other animals it is very rare. If a horse contracts the disease about 40 percent will die. Vaccinated animals require a booster shot at two to three weeks after the initial vaccine and your animal will not have coverage against the disease until two weeks after the booster. Doctor Jensen recommends all horses be vaccinated next spring.