Rabies hitched a ride to Canada in dogs flown from Iran. Scientists caught the spread just in time
New review paper highlights importance of surveillance for new strains of viruses, bacteria
This story is part of CBC Health's Second Opinion, a weekly analysis of health and medical science news emailed to subscribers on Saturday mornings. If you haven't subscribed yet, you can do that by clicking here.
When two dogs imported to Canada from Iran on separate occasions in 2021 developed deadly canine rabies, alarm bells rang loudly for public health officials. They scrambled to trace dozens of people who may have been in contact with the animals' saliva to give preventive treatment before it was too late.
The quick action staved off what could have become a fatal disease in at least 60 people, including the dogs' foster and adopted families, their friends, as well as staff at several veterinary clinics across Ontario.
For epidemiologists, cases such as those underscore the importance of surveillance for new strains of viruses and bacteria coming into Canada by way of animals, a subject highlighted in a review paper published in Science Translational Medicine last week.
"It's pretty concerning for individuals when they're told that a dog you came in contact with had rabies," said Dr. Tasha Epp, a veterinarian and epidemiologist at the University of Saskatchewan in Saskatoon tracking diseases that can be transmitted between animals and humans.
Epp is among several researchers on the lookout for more dog rabies in North America. The authors of the review paper apply the same principles to other illnesses originating in wild and domestic animals.
Prevention and control key
While wild animals act as carriers for rabies in Canada, human cases are extremely rare. Still, doctors recommend staying clear of wildlife and seeking treatment if bitten.
Canada has been free of the canine form of rabies for decades, which federal public health officials say is thanks to excellent prevention and control programs.
But the recent scare has them looking at precautions and tightening cross-border rules.
The challenge comes from how long the rabies virus can incubate in a dog before it starts changing its behaviour, such as becoming uncharacteristically aggressive.
Rabies is typically transmitted to people from the bite of a rabid animal through direct contact with its saliva (such as through broken skin or membranes in our eyes, nose or mouth). It affects nerves. People can first feel tingling around the wound or scratch, then weakness, fever or headache. Muscles can become paralyzed followed by coma and eventually death.
In the first of the two 2021 cases of dog rabies, the three-month-old puppy that arrived from Iran didn't need to be quarantined because it was a personal pet.
The pup had no known exposure to wildlife carriers in Canada.
WATCH | Packed animal shelters seek relief:
Seven months after arriving, however, the puppy developed neurological symptoms and was eventually euthanized.
"You can't just say, 'OK, well, if we watch them for a couple of weeks after they arrive, they're good,'" said Scott Weese, who specializes in infectious diseases at the Ontario Veterinary College at the University of Guelph.
"They can incubate the disease for quite a long period."
It's possible the dog was properly vaccinated with a valid certificate and a good quality vaccine, Weese said.
"It was just too little, too late because it had been exposed beforehand."
Vaccinate and don't leave unsupervised, say experts
In the second case, public health officials with the Simcoe Muskoka District Health Unit based in Barrie, Ont., found 24 individuals who had contact with a dog diagnosed with rabies.
Of these, 14 were considered exposed and received post-exposure prophylaxis — immunoglobulin and vaccines to stop the virus in its tracks — at an average cost to the province of about $2,000 per person.
Steven Rebellato, vice-president of the environmental health department at the Simcoe Muskoka unit, worked on the investigation.
Rebellato said pet dogs, cats and ferrets over three months of age, as well as certain horses, cattle and sheep, need to be vaccinated against rabies by a licensed veterinarian and with an approved vaccine. Similar laws exist across Canada.
He also encouraged pet owners to protect their animals from rabies by ensuring they don't wander unsupervised, especially at night when bats, foxes, raccoons and skunks are most active.
Import rules and loopholes
Travellers may be at risk of contracting rabies. In many countries outside North America, health officials flag dog rabies because of domestically acquired infections and factors such as a lack of readily available post-exposure treatments.
Epp heads a project to check that newly imported dogs aren't bringing new forms of pathogens, such as canine rabies, into the country. She's still recruiting participants and is pleased the dogs have been in good shape so far. Researchers in Ontario used an online questionnaire for a similar project.
While Ukraine is listed as one of the high-risk countries for dog rabies, Canada's rules allow people to bring in their pets on compassionate grounds, and some of the people fleeing the war in Ukraine made use of that, said Epp.
"As long as they're fully vaccinated, and they come through that system, there's always some little loopholes … in terms of where dogs are coming [from] and why are they coming."
The Canadian Food Inspection Agency's "imported dog" category is a broad one. It lumps in everything from well cared for rescue dogs and dogs owned by Canadians returning home who spend part of the year in the U.S. to illegally trafficked animals from puppy mills and elsewhere that pose health and welfare risks, Weese said.
Infections rise and awareness lags
Virology professor Gary Whittaker at Cornell University in Ithaca, N.Y., who co-authored the recent review paper with his colleagues, says the animals that can transmit infections to humans range from companion dogs, cats or horses to wild birds or backyard chickens and other creatures that pass through yards or parks: think raccoons, bats, squirrels, coyotes or skunks.
"We've got a changing dynamic in pet ownership, and I think that's what is concerning me the most," Whittaker said. "Our awareness of diseases isn't really keeping up to pace."
Indoors, when a large, dense population of cats or dogs are in close proximity at shelters or moving between foster homes, kennels or doggy daycare, it's an opportunity for superspreader events of influenza to occur, he said.
Superbugs from raw pet food
Whittaker and other scientists are also keeping a close eye on antimicrobial-resistant bugs and have zeroed in on trendy raw pet food because of its potential to spread such bugs between cats, dogs and people and vice-versa.
"There is at least one [human] death identified in the U.K. a few years ago from E. coli O157 that was in a pet diet," Weese said.
"Diet can definitely play a role in health, but there's not really any indication for a raw diet. They bring in extra risk and cost without conferring extra benefits."
Pets rarely pass on multi-drug-resistant infections, or superbugs, that they've picked up in raw food to us, but that risk could be reduced to zero if we dispensed with raw pet food altogether, he said.
Another way to help combat the problem, he said, is for farmers and veterinarians to avoid giving livestock, including poultry, unnecessary antibiotics so that medical doctors still have them available to fight infections in humans.