HEALTH

Curtailing a maddening disease

Researchers are looking for better ways to rid wildlife of rabies epidemics

June Rogers August 3 1981
HEALTH

Curtailing a maddening disease

Researchers are looking for better ways to rid wildlife of rabies epidemics

June Rogers August 3 1981

Curtailing a maddening disease

Researchers are looking for better ways to rid wildlife of rabies epidemics

HEALTH

June Rogers

Don Coulter’s herd of 100 brood cows—worth a hefty $70,000— each yield a good 10 years of calf production. So it was understandable that, this spring, he worried at the sickliness of a one-year-old heifer he had raised from a calf. When the vet from nearby Moose Jaw, Sask., informed him the animal had been bitten by a rabid skunk, the farmer was shocked. Says he: “This was the first time in my 15 years of farming any of my livestock has had rabies.” To keep the rest of his animals from contracting the disease, Coulter immediately quarantined his heifer. Three days later, she was dead.

While this was Coulter’s first encounter with the disease, positive (or confirmed) cases of rabies among domestic and wild animals are on the rise in Canada—primarily in Ontario, although a small epidemic is now burgeoning in southeastern Alberta, too. Last year, out of a suspected 9,235 cases across the country, 1,659 proved to be rabid. These rising numbers of diseased animals pose a direct health hazard to humans: a rabid marauding fox might infect a dog, which in turn might endanger a human. In fact, more than 1,100 Canadians received post-exposure

vaccinations last year. Says Dr. Ross Singleton of Agriculture Canada in Winnipeg: “We’re inundated with calls from people who are concerned about the problem.” Underlying the general alarm is the real concern —how to control the outbreaks in the wildlife population.

Ontario faces a unique challenge in rabies control. The province has the dubious honor of claiming the highest number of rabies cases in all of North America. The reason: it boasts Canada’s largest population of foxes and skunks, the most ubiquitous vectors of rabies. Just last year, they accounted for a total of more than 1,000 positive cases. Until recently, total destruction of the affected species has been virtually the only way to curb rabies in the wildlife population (domestic animals, such as dogs, cats and livestock, can be vaccinated). But now, the Ontario ministry of natural resources together with the University of Toronto and Connaught Laboratories is developing the first oral vaccine in Canada for non-domestic animals. Depending on the results of current laboratory experiments on foxes—preliminary reports cite a 50per-cent success rate—the researchers will receive permission from Agriculture Canada to conduct the first field

trial this fall. Trappers near Goderich, Ont., will capture a small number of foxes; researchers will then hand-feed the vaccine to them and tag them for a follow-up.

As recently as 40 years ago, rabies was practically unheard of in Canada, and then only in arctic wolves and foxes. But they began contaminating their southern relatives, and the disease spread. The very word rabies conjures up grotesque images of foaming mouths and convulsions. In essence, this disease occurs only in mammals and is caused by a virus that invades the body through a wound. Its incubation period can last up to six months, but once acti-

vated, it attacks the nervous system and then travels into the saliva. When a rabid animal bites, the saliva transmits the virus. Even after the sick animal dies, the disease can be passed on if a scavenger consumes the carcass.

The primary sources of human exposure to rabies are cats and dogs and, to a lesser extent, farm animals, all originally infected by diseased wildlife. But rabid non-domestic animals that wander into cities also jeopardize people, i “We’ve had kids in Saskatoon chase skunks,” says Gary Wobeser, a pro1 fessor of veterinary pathology at the University of Saskatchewan, “that turned out to be rabid.” Although the last confirmed case of rabies in a hu-

man occurred a decade ago (a rabid bat wounded a Saskatchewan boy who eventually survived), anyone exposed to rabies must be inoculated with an antirabies serum or risk death.

Controlling rabies in the wild is problematic because animals tend to migrate and their numbers fluctuate. In the early ’50s, Alberta experienced a more severe outbreak of rabies than Ontario is undergoing now. “There were several thousand cases of rabies among the wild and domestic animal population,” says Joe Gurba, head of the pest control branch at Alberta’s ministry of agriculture. “It was really a grim situation.” When a case of rabies was reported—for example, in a coyote—a crew would destroy that species’ total population within a five-kilometre radius. Then in the late ’60s, a rabies outbreak in the skunk population prompted provincial authorities to set up a buffer zone along the Saskatchewan border to stop the overland movement of rabid animals. The program proved so successful that it is still in use today. The buffer zone was consequently extended and now stretches 600 km long and 30 km wide along the Montana and Saskatchewan borders. “It’s inhumane,” says Gurba, “but so is rabies.”

Opponents of such a drastic measure argue that decimating an area’s indigenous population causes ecological imbalances. What’s more, they say, the population rebuilds so quickly that the process must be repeated often. “Most think depopulation is not a permanent solution,” notes Dr. Ken Charlton, head of the rabies unit at Ottawa’s Animal Diseases Research Institute. But Alberta does enjoy an enviable record: authorities report only 90 cases of rabies in the past decade. Even its present outbreak is being methodically confined to the southeast corner of the province.

Alberta’s program would be impractical in Ontario because of its dense populations of wild animal carriers. The only plausible solution left to researchers was to develop a vaccine. If this fall’s field trial is successful, a large-scale vaccination program will occur next year. Says University of Toronto microbiologist Jim Campbell, who is working on the vaccine: “We’re aiming at immunizing at least 50 per cent of the fox population so that the remaining susceptible foxes will be protected.” The vaccine will be hidden in hamburger bait (which successfully appealed to foxes’ and skunks’ finicky tastes in a test run last year) and airdropped into rural areas. Many experts in rabies control will be watching the Ontario program with keen interest. Says Charlton: “If the vaccine works, the rewards will be significant.”

With files from Jim Essex.