By Jordan Omstead
A rise in mammals infected with bird flu has put Canadian wildlife and public health experts on alert, as recent research by federal scientists warns of a "potentially devastating pandemic" if the virus tearing through poultry flocks eventually mutates to spread efficiently between humans.
Avian influenza cases are very rare in humans – there have been fewer than a dozen confirmed H5N1 cases globally since 2020 – and no instances of it passing from human to human. But experts say public health agencies are right to keep a close eye on how the highly pathogenic avian influenza H5N1 evolves.
"There are enough red flags that we’re beholden to prepare," said Dr. Samira Mubareka, an infectious disease specialist and clinician scientist at Sunnybrook Research Institute and the University of Toronto.
H5N1 was first identified in 1996, but a new type of the virus emerged in 2020. It was first detected in North America in late 2021 and has since decimated flocks of wild and domesticated birds, resulting in millions of poultry deaths across Canada either from infection or culls to prevent its spread.
While cases in mammals are to be expected during a bird flu outbreak, Mubareka said part of what's captured the attention of scientists is the range of species infected.
"If the virus spills over into new species, it always gains an opportunity to mutate and adapt even further," she said. "So this is really an unprecedented level of viral activity for H5N1."
Last week, the first Canadian case in a pet dog was reported, adding to hundreds of confirmed cases in wild skunks, foxes, mink and other mammals since the start of last year. This month, three outbreaks were confirmed at poultry operations east of Montreal and a fourth at a farm west of London, Ont., with farmers bracing for a possible wave of cases as migratory birds return this spring.
Public health agencies in Canada, the U.S. and Europe agree the risk to human health remains low, with cases almost always limited to direct contact with infected birds or contaminated environments, such as a poultry barn. There is no risk associated with eating thoroughly cooked poultry products.
Scientists, however, are studying the virus closely.
In a paper published last month, scientists with the Canadian Food Inspection Agency working out of a lab in Winnipeg, where Canadian cases of H5N1 are confirmed and genetically sequenced, looked at cases in 40 different wild mammals. The researchers found the virus had undergone some "critical mutations," though the agency said the chances of human spillover remains minimal.
"The spillover of these viruses from wild birds to mammals could cause a potentially devastating pandemic if the H5N1 viruses mutate into forms that can spread efficiently among the mammalian species," read the paper, published in the peer-reviewed journal Emerging Microbes & Infections.
The critical mutations researchers uncovered involved part of the virus that helped it make copies of itself, adding to similar findings reported globally. In 17 per cent of the cases, the scientists found changes that gave the virus better advantages to replicate in humans.
But, in an encouraging sign, the researchers wrote the virus had not developed a strong preference to lock on to receptors in a person's nose, mouth and throat – the target of an influenza virus and a key to human infection.
The Public Health Agency of Canada said it takes the situation "very seriously," with multiple surveillance networks to monitor and track influenza viruses. Together with lessons learned from the COVID-19 pandemic, it said it has been able to build H5N1-specific plans across government departments.
Shayan Sharif, professor and acting dean at the Ontario Veterinary College, said he is most concerned about the possibility that the virus is going to change to the point where it becomes more dangerous to humans and gains the capacity for human-to-human transmission.
"I don't think that this virus is going to go anywhere," he said. "I hope that I'm wrong."
The U.S. Centre for Disease Control said it recently produced a candidate vaccine virus for H5N1 that could be used to produce a vaccine for people, if needed.
As for poultry, Canada, along with the U.S., has so far been reluctant to roll out an H5N1 vaccine campaign for the birds, but it's a step Sharif said the government should consider.
The European Union's 27 member states have agreed to implement a bird flu vaccine strategy, with Mexico, Egypt and China on the growing list of countries inoculating chickens against H5N1.
Sharif, whose expertise is in avian influenza immunology in chickens, said targeted vaccination could help prevent poultry losses and reduce the spread of the virus, but it has also proven controversial given some import trade bans on vaccinated poultry over fears the birds could unintentionally introduce the virus.
Marc Betrand, a veterinary specialist with the CFIA, said Canada is not ready to roll out a vaccine strategy. The H5N1 chicken vaccines "are not that efficient," he said, and could end up triggering more mutations to the virus.
The CFIA, which heads up the federal response to H5N1 in farmed birds, said measures such as routine cleaning and isolating new birds are key to prevent outbreaks.
Avian flu has also been hitting wild bird populations in a "completely unprecedented" way, said Catherine Soos, a wildlife disease specialist and a research scientist with Environment Canada.
The federal agency is charged with monitoring migratory birds and species at risk. It will be keeping a close eye this spring on migratory bird populations returning north, bringing potentially new versions of the virus, Soos said.
It's also watching to see how certain wild bird species hit hard by H5N1 bounce back this year. About 1,600 breeding female Common eiders turned up dead last year along the Gulf of St. Lawrence, an estimated five to 15 per cent of the population, Soos said.
"We definitely want to monitor these populations," she said.
Banner image: Dr. Samira Mubareka, an infectious disease specialist and clinician scientist at Sunnybrook Research Institute and the University of Toronto, poses in this undated handout photo. THE CANADIAN PRESS/HO-Sunnybrook Hospital
This report by The Canadian Press was first published April 13, 2023.
