West Nile Virus - Protect Yourself and Your Horse Practical Advice for Horse Owners

Table of Contents

  1. Introduction
  2. WNV Vaccination
  3. Signs of West Nile Virus
  4. The West Nile Virus


WNV is a serious emerging disease. You should take precautions to protect both yourself and your horse.

  1. Consult your veterinarian about vaccinating your horse for WNV and other diseases.
  2. Eliminate potential mosquito breeding areas on your property. Clean up and empty containers of standing water such as old tires or barrels. Change water in troughs and birdbaths frequently. Clear leaves, twigs and other debris from rain gutters and drainage ditches.
  3. Add extra protection to avoid mosquito bites. Use flyspray, a flysheet and flymask on your horse.
  4. Refrain from outdoor activities during peak mosquito activity times at dawn and dusk.
  5. Protect yourself by wearing light coloured long sleeved shirts and long pants. Use a mosquito repellent containing DEET (N,N-diethy-m-toluamide). Be careful to read and follow all label directions for use.

WNV Vaccination

There are two WNV vaccines approved for use in horses. They have been widely tested and are safe to use.

The initial vaccination requires two injections three to six weeks apart followed by an annual booster. A booster vaccination every six months is recommended for horses at higher risk, such as those travelling to areas of the U.S. or other countries where mosquito populations survive year-round. For full protection, vaccinations should be initiated two months prior to the start of the mosquito season.

Talk to your veterinarian about a complete vaccination program to protect your horse from WNV and other diseases.

Signs of West Nile Virus

Often the first signs of WNV in a region are unexplained bird deaths. Report any unusual sightings of dead crows or jays to your local public health unit.

WNV infection in horses affects the central nervous system. Symptoms range from listlessness, trembling, depression, loss of appetite, stumbling and in-coordination, weakness, head tilting and partial paralysis, to convulsions and even death. Fever occurs in 25% of cases. These symptoms can appear very rapidly and are similar to other nervous system diseases including rabies and equine encephalitis. Up to one-third of all horses showing clinical signs of WNV will die.

Consult your veterinarian immediately if you observe any symptoms of WNV or other nervous system disease in your horse. Your veterinarian will begin supportive treatment, collect samples and request laboratory tests to identify causes of disease. In the case of death, a post mortem examination and follow-up testing is recommended.

Should WNV be detected in your area, be aware that the infection is spread through mosquito bites. There is no evidence that the virus can be directly transmitted to people from infected birds or horses. Persons infected with WNV usually experience mild flu-like symptoms, however, the virus can cause severe illness and even death. The elderly and individuals whose immune systems are already compromised by another disease condition are at higher risk.

The West Nile Virus

West Nile Virus (WNV) first appeared in North America in 1999. This mosquito-borne virus can infect many different animal species but crows, jays, humans and horses are at higher risk.

Ontario first detected WNV in birds and mosquitoes in 2001. Evidence of the virus was found throughout the province in 2002 and, by fall, both human and horse WNV infections were confirmed. In 2002, WNV was the probable or confirmed diagnosis for 107 cases of encephalitis in horses. In 2003, 2004 and 2005, WNV was confirmed in 10, 9, and 5 cases of encephalitis respectively.

For further information about West Nile Virus and horses contact:

Or your local Public Health Unit.

For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: Dr. B. Wright - Lead Veterinarian, Equine and Alternate Species/OMAFRA
Creation Date: February 2002
Last Reviewed: August 2006