Despite elevated levels of viral activity this fall, statewide reports of West Nile have decreased significantly — a feat the state veterinarian attributes to high vaccination rates.
The state has seen just three confirmed cases of West Nile in horses this year — a notably low number, especially during a year where West Nile is popping up in numerous mosquito pools across the state, said Warren Hess, acting state veterinarian.
“It’s been relatively active in the mosquito pools,” he said, “but we credit the people vaccinating their animals.”
The West Nile Virus vaccine, which is effective in horses and thought to be effective in birds but ineffective in humans, is commonly available from most local veterinarians, according to Hess. But it can also be bought and administered by the animals’ owners, said Joe Roundy, a veterinarian at the Tooele Veterinary Clinic. The vaccine must be administered once a year, like a flu shot, to remain effective.
Roundy said he has never seen a horse infected with West Nile locally, despite watching for any sign that the virus is spreading among Tooele County’s equine populations. He too credited the vaccine for reducing the spread of the disease.
“People are really good about vaccinating their horses, and I think there has been enough of it around that they’ve developed a natural immunity,” Roundy said.
However, he added that local vaccination rates are not high enough that owners should let their guard down and slack off on their horses’ vaccinations. About half of the horses Roundy treats are vaccinated for West Nile, he said, but he would like to see that number near 80 to 100 percent.
“If we’re going to make any dent in trying to reduce the instances of the disease, 80 percent is a minimum,” he said. “Otherwise the virus keeps multiplying and spreading.”
As with humans, only about half of the horses that contract West Nile actually show symptoms of the disease, Roundy said. But those horses that do can become extremely ill.
According to a press release from the Utah Department of Agriculture and Food, West Nile attacks the central nervous system and causes weakness, fever, depression and fearfulness in horses. In severe cases, the disease can cause paralysis.
About one half of horses that contract the virus will die because there are no anti-viral drugs available to counter West Nile, Roundy said.
“We just end up treating symptoms, and so half of them are going to die despite treatment,” he said.