By Joe B. Baker, DVM
Washington State Veterinarian
One week ago the count of horses confirmed with West Nile
virus in our state totaled 10 cases. As of Wednesday, it has climbed to 18
cases.
The first case was reported in late July in Benton County,
and since then there have been cases reported in six more counties, including Adams,
Franklin, Grant, Kittitas, Lincoln and Yakima counties. The south-central portion
of our state has historically been where most of the West Nile virus infections
are documented each year. After experiencing a significant number of cases in
the region in 2008 and 2009, there had been relatively few cases in horses
reported in 2010-2014. Five cases were reported in 2014.
 |
| Photo: Erin Danzer |
Unfortunately, none of the horses reported this year had
current booster shots for West Nile, and many of them had never received any
vaccination for the disease. After several consecutive years with few or no
cases, horse owners may have been lulled into thinking that vaccinations for
West Nile virus did not have to be included in their horse’s annual shots. In
one case the owner had reportedly been advised by their trainer that
vaccinations in horses were a waste of time.
About half of the virus-infected horses reported this year
in our state have either succumbed to the disease or have been euthanized. Statistically,
40 percent of those horses that recover will be likely to have long-lasting if
not permanent neurological deficits.
I would like to make a personal plea to all horse owners in
Washington to include a West Nile virus shot as a core vaccine in your horse’s
vaccination schedule. The American
Association of Equine Practitioners considers the core vaccinations for horses
to be eastern/western equine encephalitis, tetanus, rabies and West Nile virus.
The American Veterinary Medical Association defines core
vaccinations as those “that protect from
diseases that are endemic to a region, those with potential public health
significance, required by law, virulent/highly infectious, and/or those posing
a risk of severe disease. Core vaccines have clearly demonstrated efficacy and
safety, and thus exhibit a high enough level of patient benefit and low enough
level of risk to justify their use in the majority of patients.”
Typically Washington’s mosquito season lasts until freezing
temperatures return in the fall. If you have a horse that has been given West
Nile virus vaccine in the past, it is not too late to give it a booster.
Boostering a previously vaccinated horse usually induces a rapid rise in immune
levels. If you have never vaccinated your horse in the past, it will take two
shots about a month apart to establish immunity. So you could still manage to protect your
horse for the last few weeks of this year’s mosquito season if you start now!