Correction: A story on page 25 of the Jan. 23 issue, about vaccination of horses for West Nile virus, requires clarification. Larry Frischke of Wyeth Animal Health says the correct vaccination protocol is two doses: an initial dose followed by a booster in three to six weeks. Annual boosters are recommended after that. In high risk areas, a booster may be administered four to six months after the second of the initial two doses. Vaccinations should be timed so the horse has full immunity for the start of mosquito season.
RED DEER – Educators and regulators must work together to control West Nile virus, says Bill Saville of Ohio State University’s veterinary medicine department.
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Transmitted by certain species of mosquitoes, this zoonotic disease is known to infect birds, horses and people.
Saville, an internationally known authority on the disease, said that as more is learned about it, better controls and vaccines can be developed.
Originally from Alberta, he spoke at a horse breeders and owners conference in Red Deer Jan. 11-12.
Les Burwash of Alberta Agriculture’s horse industry branch said West Nile is not a reportable disease in Alberta, but the department plans to mobilize so the province is ready if the disease strikes.
Wyeth Animal Health, formerly called Ayerst, provides a conditional vaccine available only through veterinarians.
Larry Frischke of the company said the first vaccination is needed three weeks before mid-April followed by two doses, three to six weeks apart, annually.
The pregnant mare’s urine industry, for which Wyeth is a major buyer, insists that all animals under contract be vaccinated followed with annual boosters.
“We could see cases in Alberta by the fall of 2003,” he said.
There is no vaccine for people and the long-term effects for those who survive the infection are unknown.
There are two strains of the disease. The more virulent one arrived in North America in 1999, possibly when disease-carrying mosquitoes were trapped on airplanes or container ships.
It first appeared in Uganda in 1937 and spread throughout Africa, the Middle East, Europe and Asia.
In 1994, Morocco lost nearly half its horses to the disease and millions of geese died in Israel.
So far, 111 species of birds have tested positive for West Nile. Crows, magpies, blue jays, blackbirds and ravens are most susceptible.
Infected birds have crooked wings and neurological problems and usually die.
Most affected horses display stumbling and a lack of co-ordination. Lesser symptoms include depression, profound weakness, muscle tremours, fever, paralyzed or droopy lip, twitching muscle, teeth grinding and, on rare occasions, blindness.
Some horses become aggressive and agitated. This behaviour may also indicate rabies or botulism, so tests are required.
The incubation period in horses and humans is five to 15 days.
Canada had about 100 horse cases in 2002 and 121 cases of human West Nile virus from Nova Scotia to Saskatchewan. It was first confirmed in Canada in Ontario in a dead bird in August 2001.
