West Nile Virus Found in Saskatchewan Horses

REGINA, Saskatchewan, Canada, September 10, 2002 (ENS) - Six horses in Saskatchewan have been diagnosed with West Nile virus, according to officials at the Saskatchewan Agriculture, Food and Rural Revitalization's animal health unit. This is the first confirmed case of equine West Nile virus in the province and marks the farthest west that the virus has been found in Canada.

The virus was detected in birds in Manitoba in early July, and has now been found in some locations in Saskatchewan. On September 4, Saskatchewan confirmed its first positive case of the virus in horses when brain tissue submitted to the National Centre For Foreign Animal Disease in Winnipeg for tested positive. Five other positive samples were reported from the same lab.


A few of the 123,000 horses in Saskatchewan. These horses are not infected with West Nile virus. (Photo courtesy Jacob Ranch)
Provincial animal health officials are encouraging horse owners across this largely rural province to take preventative measures. A vaccine can be obtained through veterinarians for conditional use.

The West Nile virus vaccine for horses is not licensed for use in Canada but can be obtained as a conditional use vaccine only through veterinarians who must keep detailed records.

The "conditional" nature of this vaccine means preliminary trials have been conducted to determine the safety of this vaccine along with an immunogenicity study showing favorable results, according to Ayerst Veterinary Laboratories which supplies the vaccine in Canada. The safety study performed on 649 horses showed no local or systemic adverse reactions following 98.8 percent of the vaccinations administered, Ayerst says. Further trials and efficacy data remain under review and are required for full commercial approval in Canada.

West Nile is a type of virus that causes encephalitis, or inflammation of the brain. The virus has been found in Africa, western Asia, the Middle East, the Mediterranean region of Europe and in the United States since 1999. Mosquitoes become infected with the virus after feeding on infected wild birds and then transmit the virus through bites to people, animals and other birds.

Horses become infected with West Nile virus in the same way people do, by the bite of infected mosquitoes.

Many horses will develop mild infections that are not apparent, and Saskatchewan officials say there is no reason to destroy a horse just because it has been infected with West Nile virus. "Data suggest that most horses recover from the infection. Treatment would be supportive and consistent with standard veterinary practices for animals infected with a viral agent," the agency advises.

In more susceptible horses the virus will leave the blood and enter the brain and spinal cord where its causes inflammation and interferes with normal central nervous system function, leading to severe clinical disease or death of the horse.

Saskatchewan animal health officials say that the horse is "a dead-end host for West Nile virus." The virus does not spread from horse to horse, or to other animals, including humans.

Illness due to West Nile virus has not been found among sheep, pigs, and cattle. The main reservoir for the virus is thought to be wild waterfowl.

Preventative measures center on mosquito control. The Saskatchewan agency advises owners to stable horses at night in a barn with mosquito netting in place, and use insect sprays and repellants. Where permitted, burn smudges to reduce mosquito activity near horses. Reduce the amount of tall vegetation around corrals and barns, and get rid of all sources of standing, stagnant water, animal health officials warn.