What is West Nile Virus?
West Nile Virus came to the United States in 1999. The virus infects birds where it replicates itself to high levels. Mosquitoes feed on these birds and spread the virus to other birds, some other animals, and rarely people.
How does a horse catch it?
Horses contract West Nile Virus when they are bitten by an infected mosquito. For this reason, West Nile Virus is considered a Core Vaccine (a vaccine recommended for every horse, even horses that never leave their home and aren't exposed to other horses at events).
What are the symptoms in horses?
Fortunately, most horses don't show symptoms. For those that do, the most consistent sign is weak, uncoordinated hind legs. Twitching in the face and muscle tremors can be seen. The horse may or may not have a fever, and may still eat well. They resemble a horse with a back or hip injury or a totally different disease called EPM.
You may have heard it in the news, but last fall there was a horse that tested positive in Sauk County (actually it was in Wisconsin Dells). I treated this horse (plus another one with the same symptoms at a nearby property). Both horses showed difficulty standing up for a few days. Once they were standing, they looked normal. After a couple days, however, they had no strength in their hind legs and could not stand. Neither had fevers or significant changes to routine blood testing. I saw a couple other horses in the area that showed hindlimb weakness but the owners declined testing.
Is it treatable?
There is no specific treatment to kill the virus. Medications to reduce swelling in the spinal cord and limit damage to nerves are used. If the horse can't stand up, they need to be hospitalized in a sling to hold them up, and may need IV fluids and other intensive care.
Is it preventable?
Limiting mosquitoes in your horse's environment is ideal, but difficult!
Fortunately, we have excellent vaccines for West Nile Virus. Horses should be vaccinated in spring or early summer so the horse will have protection through our mosquito season. Horses that will be in the south in the winter should be boostered again in the fall.
Horses that have not been vaccinated for West Nile Virus before need two doses a month apart for full protection and then vaccinated annually. When Dr. Sholts or I administer the vaccine and your horse has been kept up to date, your horse is part of an assurance program. If your horse would show symptoms that COULD be West Nile Virus, the vaccine company we use will pay for your horse to be examined, tested, and treated.
West Nile Virus vaccines can be given as a stand alone vaccine, in combination with EEE, WEE, and tetanus, or in combination with EEE, WEE, tetanus, influenza, and rhino. A lot of owners are familiar with a "5-way." The 5-way vaccines I have seen are EEE/WEE/tetanus/influenza/rhino. They are appealing because they are inexpensive, but the reason they are inexpensive is that they do not have West Nile Virus in them.
We're here to help! If you have any questions about your horse's vaccination status, please give us a call.