PORTLAND, Ore. -

Now that spring has officially arrived, Oregon veterinarians are reminding equine owners that this is the season to make sure your horses have been vaccinated against West Nile Virus (WNV) or have received their booster.

West Nile Virus affects humans, horses, and many types of birds. It is carried by mosquitoes, and transmitted through a mosquito bite. Birds are considered to be reservoirs of the disease.

West Nile Virus Cases in Oregon

In 2012, two horses in Klamath County tested positive for WNV and one died. One of them, a 12 year old mare, had not received its annual WNV booster. Positive WNV mosquitoes were detected in Jackson, Malheur and Morrow counties. A total of 12 Oregonians were infected with WNV. Of those, nine contracted the infection though mosquito bites in Oregon—one in Coos County and eight in Malheur County. All recovered. Humans can only get the virus from the bite of an infected mosquito; the disease does not spread from horses or other animals to humans, nor from person to person.

Symptoms of the Virus in Equines

According to Dr. Wayne Schmotzer, DACVS, an equine specialist with Bend Equine Medical Center, “The virus causes inflammation of the brain and spinal cord. Equines that contract the virus can experience lack of coordination, stumbling, confusion, fever, stiffness, muscle twitching, depression, and weakness in the legs. About one-third of infected horses die.”

Protect Your Horses Through Immunization

The virus has become endemic in Oregon, so it is important to vaccinate your horses. The vaccine requires two doses given three to six weeks apart. Immunity may not be achieved until up to six weeks after the second dose, and some horses may require a third vaccination. An annual booster should be given in accordance with the vaccine manufacturer’s instructions and ideally prior to the start of the mosquito season in your area.

If You Suspect Your Horse is Infected

Contact your veterinarian for an examination. Veterinarians are required to report horses showing clinical signs. If your veterinarian believes your horse may be infected, testing is available at no charge through the Oregon State University Diagnostic Laboratory.

Minimize the Threat of Exposure for You and Your Horses

The best way to minimize the threat of West Nile Virus is to control mosquito populations and prevent exposure to them:

  • Eliminate sources of standing water that can serve as a breeding ground for mosquitoes, including old tires, buckets, wading pools, and other containers. Change water in bird baths weekly
  • Report the suspicious illness or death of birds to your county health department or to Oregon Fish and Wildlife at (503) 947-6322.
  • Consider avoiding outdoor activities from dusk until dawn or take extra care to use repellent and protective clothing during evening and early morning. When possible, wear long-sleeves, long pants and socks when outdoors.
  • Treating clothes with repellents containing permethrin, DEET or oil of lemon eucalyptus will provide extra protection, since mosquitoes may bite through thin clothing. Please follow the manufacturer's recommendations regarding proper and safe application of any repellant, especially on children.

With acknowledgement to Dr. Emilio DeBess, State Public Health Veterinarian, Oregon Health Authority.

About the OVMA: The Oregon Veterinary Medical Association is a nonprofit organization of over 1,000 veterinarians who are dedicated to helping people give their animals a high quality of life. oregonvma.org