Horse owners should consult with their veterinarians to develop a vaccination plan for West Nile virus specific to their animal and situation, the Montana Department of Livestock advises.

The best time to vaccinate is before mosquito activity begins, as the vaccine takes a few weeks to offer full protection. Montana’s animal health officials note there was a spike in the number of West Nile virus cases last year.

“We had 32 cases last year, the most since 2007, and the third highest total in the nation,” assistant state veterinarian Dr. Tahnee Szymanski said. “That’s concerning because the disease is highly preventable.”

Stressing the importance of vaccination, Szymanski said, is that there is no treatment for horses that contract the disease.

Based on MDOL data, no equines that were current on vaccinations have ever contracted the disease in Montana. In contrast, one-third of the non-vaccinated equines that contracted the disease either died or had to be euthanized, a total of 161 of 492 since 2002.

Dr. Greg Johnson, professor of veterinary entomology at Montana State University’s Department of Animal and Range Sciences, says vaccination — which is recommended as a core vaccine by the American Association of Equine Practitioners — is prudent given West Nile virus’ unpredictability.

“It’s kind of like the flu season,” Johnson said. “We can look at the existing data and forecasts and make some guesses, but we can’t really predict what West Nile virus is going to do or how bad it’s going to be.”

With snowpack running at 150 percent of normal throughout much of Montana, environmental conditions could be right for West Nile virus activity later this year.

“With all of that snowpack, it looks like we’ll have lots of water, and that can mean more mosquitos,” Johnson said.

A mosquito-borne disease, West Nile virus was first found on the east coast of the U.S. in 1999. Since then, the disease has spread westward, arriving in Montana in 2002. The disease knows no climactic or geographic boundaries in Montana and has been found statewide.