West Nile Virus In Horses

What is West Nile encephalitis?

Here is one definition; “West Nile encephalitis describes an inflammation of the central nervous system, which is caused by infection with West Nile Virus. Prior to 1999 West Nile Virus was found only in Africa, Eastern Europe, and West Asia. In August of 1999 it was identified in the United States.”

To break it down and define some of the terms - so it’s at least more interesting reading - “encephalitis” means a “disease of the central nervous system (CNS). So, simply said, West Nile Virus (WNV) is a disease of the CNS.

A Quick History of WNV

The name “West Nile Virus” comes from the West Nile District of Uganda in Africa, the place in which it was first recognized in humans. The year was 1937. It is reported that horses were first known to be infected in Egypt and France in the early 1960s. Up until its documentation in the US in 1999, WNV was already known in Africa, the Middle East and in parts of southern Europe.

Apparently the first US epidemic in horses was diagnosed in New York City, and later in Long Island, New York. Because of the location of the epidemic it is suspected that WNV was brought in by an infected bird or mosquito via ship or airplane. No one knows for certain. Regardless, the disease is – unfortunately - here to stay.

Symptoms of WNS

When a horse is infected with WNV he/she may or may not display any symptoms. If you suspect your horse may be infected with this disease you are obligated to contact your vet immediately.

If symptoms do appear they range from fever, weakness or paralysis of hind limbs, slow movement, loss of appetite, inability to swallow, lack of coordination, weakness, idle wandering in the pasture, depression, muscle and/or muzzle twitching, head pressing (a horse will extend its head forward and pushes or presses it against a wall or other object repeatedly), impaired vision, convulsions, an inability to swallow, hyper-excitability, and coma. A horse may display one or more of these symptoms.

Most horses do not show any signs of infection. Thankfully, most horses with WNV recover on their own.

How Does A Horse Contract West Nile Virus?

Horses get WNV by being bitten by an infected mosquito. It cannot be transmitted from one horse to another, or between humans and horses.

How Do I Treat A Horse With West Nile Virus?

If you haven’t done so already, contact your equine vet immediately to verify that your horse does, in fact, have WNV. A positive diagnosis can only be determined through laboratory analysis from blood serum or cerebrospinal fluid extracted by a veterinarian. Symptoms occur when the virus crosses the blood-brain barrier and causes inflammation of the spinal cord, and/ or the brain.

Since there is no specific treatment for WNV, other than supportive care consistent with standard care for a horse infected with any viral agent, follow the vet’s instructions carefully. As stated previously, most horses recover from the disease, but – depending on which source you refer to – about 24% or so of all horses that display symptoms either die or are euthanized as a result of the disease.

Your vet may administer two doses of the vaccine, 3 weeks apart if your horse is unvaccinated.

A Word of Caution

Most vets recommend a vaccination followed with annual boosters. A horse is not fully protected until at least 3 to 6 weeks after the second booster shot, according to the manufacturer. But the effectiveness of the vaccine has yet to be determined.

Read up on the side effects and do plenty of your own research so that you are fully informed, and so that you can thereby make an informed decision about the vaccination. I say this because it is a relatively new vaccine and not a great deal is known about it, or about how well it protects your horse. One site I recommend is called West Nile Virus Protection.

A horse who has a bad side effect may display some or all of the symptoms of the virus itself. I’ve had a horse display such side effects. My horse suffered for 4 days. It is very disheartening to see your equine suffer due to a vaccination.

So be sure you weigh the side effects against the chances of your horse contracting the disease and the effectiveness of the vaccine. For me, personally, the verdict is still out as to whether or not I will put my horse through the vaccine again.

Some horses display none of the adverse affects of the vaccination. Others do. Talk to your vet about any concerns you may have. Openly discuss the pros and cons of the vaccination. Stay abreast of new information about WNV prevention and treatment.

Take Active Steps against Mosquitoes

No matter what you decide you need to take active steps to make the chance of your horse contracting the disease as unlikely as possible. That means making your horse and your property as unwelcome a place as possible for mosquitoes.

Start by getting rid of any stagnate or standing water on your property. Never let water stand more than 3 days. Mosquitoes are the carriers and transmitters of WNV, so be sure to do all you can to lessen their numbers. Empty and clean water vats, bird baths, etc. regularly and add fresh water. Get rid of old containers and tires that hold water. A mosquito needs only a very small amount of water for its larvae to prosper and grow.

Regularly spray your horses’ area in order to kill flying mosquitoes. Don’t leave lights on that will attract insects. Consider environmentally-friendly methods to decrease mosquito populations on your property.

There are also supplements you can give your horses to deter mosquitoes from biting them. I’ve used a garlic supplement with great success. Your horse may smell like spaghetti sauce but it sure beats a bite from a virus-carrying mosquito!

Keep Yourself Apprised

Once again, be sure to keep yourself up-to-date on the latest information regarding WNV, the vaccination against it, and tips on reducing the threat to your horse of infection. The more informed and responsible you are about keeping your horse healthy, the better chance your horse will stay healthy.