Experts say risk of sheep transmitting disease ‘very real’
Submitted photo/Government of Yukon
Rabbitfoot Canyon — that craggy split that divides downtown Whitehorse from Porter Creek — is the last place you would think to look for a wild sheep. But that’s exactly where Philip Merchant said they have turned up in the past.
“They were just standing there, watching the cars go past,” he said.
Merchant was the animal health coordinator with Environment Yukon for 10 years, a position from which he retired in 2011. He is, by his own admission, not a biologist or a veterinarian.
During his career, he said, it wasn’t just Rabbitfoot Canyon where wild sheep turned up unexpectedly but also in the Takhini River area near the sod farm, at Vista Road Tower, and even at the Grey Mountain rifle range, near the sheep silhouette targets.
This could have severe health implications for the species if they were to come in contact with domestic sheep, Merchant said.
“We have as good an idea of where wild sheep are as any jurisdiction, but we don’t know where they want to be,” he said.
As the News recently reported, there have been rising concerns among the conservationists, outfitters, environmentalists and farmers that domestic sheep and goats can spread pathogens to wild sheep. Those pathogens can cause severe — and often fatal — pneumonia.
This has occurred in southern populations of bighorn sheep, to which thinhorn sheep — a group comprised of three species and to which the Yukon’s famous all-white Dall sheep belong — are “very closely genetically related,” according to Environment Yukon ungulate biologist Troy Hegel.
An analogy might be grizzly bears and black bears, or mule deer and whitetails, Hegel said, referring to separate but closely-related species, which are often susceptible to the same infections.
Whereas domestic sheep can carry the bacteria with few or no health consequences, wild sheep have extremely limited resistance because they have never been exposed, said Hegel. Infected sheep either die, or, if they recover, have lingering health issues. Those that recover become “shedders” Hegel said, continuing to harbour the pathogen and infecting healthy members of the herd.
Although cross-species infection is well documented in bighorn sheep, there have been no documented cases of thinhorn sheep becoming infected from contact with domestic sheep. Merchant said there are “reams of data” that this is possible, and that infection has occurred in laboratory settings.
“The guy who was doing the experiment (on thinhorns) stopped his work because he said he was sick of killing sheep,” said Merchant. “You should never confuse the absence of evidence with evidence of absence.”
Hegel agrees the risk of infection to thinhorns is real.
“It’s a real risk — the probable outcome of the disease entering the wild population … there’s no doubt it would have a drastic effect on a population that’s been exposed,” he said.
People have been bringing sheep and goats into the Yukon for much longer than Environment Yukon has been around to do public awareness campaigns, however. This begs the question: If the disease is so contagious and dangerous, why haven’t there been infections — and die-offs — documented before?
“We don’t know this hasn’t occurred (already),” said Hegel. “If it happened 150 years ago, we might not even know.”
Thinhorn sheep have “high fidelity to range,” said Merchant, meaning that they often use the same grazing areas year after year, but we only understand their range “as we define it,” he said.
Animals may come down from the mountain in search of mineral licks, said Hegel, although these are usually routes which are well known to the animals. Small numbers of animals, particularly younger ones, may go “on a walkabout,” he said, where they wander off from their herd and either wind up back with their original population or assimilate into a new one.
These movements are a “key transmission risk,” said Hegel. If one of these wanderers were to come in contact with a domestic sheep carrying pneumonia-causing pathogens and become infected, it could spread the disease into the wild population when it returns to its range, Hegel said.
“They aren’t stuck on a mountain top their entire lives — there’s animals that are moving around,” he said. “These are the ones we are concerned with.”
This wandering behaviour explains the recent and much-talked-about incident of a young thinhorn ram who hopped a fence in Dawson City to visit some domestic sheep.
The ram paid for this casual encounter with its life.
“If a wild sheep comes in contact with a domestic sheep, the policy is to destroy it so that it can’t return to its native population,” said Hegel.
“All the reports have come in, and they’ve all said the same thing — do not let these animals mix in any way,” Merchant said. “That (ram is) the canary in the coal mine.”
“All the pieces of disease outbreak are here, they just haven’t come together yet. But they always do, given enough time.”
These concerns for wild populations have lead to discussions between agricultural and environmental officials and farmers, some of who feel unfairly pressured to meet recommendations to prevent interactions. These recommendations include double fencing, or adding electric fencing, a process which is expensive and labour-intensive.
There have been some calls to ban sheep and goats from the Yukon entirely, which is the way the Northwest Territories is going, said Merchant.
Hegel said that would be a “pretty significant, non-trivial” step for the Yukon.
Merchant said most people who own sheep and goats do not make their living from them, and that the number of sheep and goats in the Yukon is relatively small.
A 2015 flyer from the Animal Health Program entitled Preventing Pneumonia in Wild Sheep, recommends farmers “consider livestock other than sheep to raise fiber, milk and meat.”
“It’s a hobby — does somebody’s hobby have the right to threaten the public interest in conservation?” Merchant said. “Without the sheep, the mountains are just mountains — so I think that anything that could threaten them needs to be looked at.”
Shelia Alexandrovich of Wheaton River Garden said the idea that the eight sheep she raises are “just a hobby” is not a true. Alexandrovich has sheep for meat and milk, as well as for fibre, which she uses to make art and sells as part of her income.
“If I took away my ‘hobby,’ I would starve,” she said. “It provides 80 per cent of my food and 50 per cent of my income.”
“(Merchant) may see me as a hobby farm, but it’s what I do full time — I’m paid in food.”
Alexandrovich has lived in the Annie Lake area — thought to be some of the best wild sheep territory in the Yukon — for 37 years and has never once seen a wild sheep on her property, she said.
Hegel said this was possible, as there might might be other factors in the environment which discourage or prohibit the movement of the sheep onto the farm.
Merchant said the farm is “within one kilometre of where I would expect to see wild sheep.”
“If I thought I’d infect wild sheep, I’d double-fence in a minute — but I’ve never seen a wild sheep here,” Alexandrovich said. “If (the government) wants their concerns addressed — and it’s a legitimate concern — consult with farmers and give them the money to do (what’s been recommended).”
Alexandrovich said she didn’t feel the recommendations took into account the importance of small-scale farming and local food security.
“How on earth do you start (a farming industry) up here?” she said. “The little fellows trying to make inroads into local food … it isn’t easy.”
All in all, Hegel likens the recommendations to seatbelts.
“You can say ‘I never wear a seatbelt, I’ve been driving for 30 years, and I’ve never been in an accident,’” he said. “And then, suddenly, you’re in an accident and you really wish you’d been wearing a seatbelt.”