Public health officials in British Columbia announced on Nov. 9 that a teenager from the Fraser Valley has contracted avian flu – the first human case of the potentially deadly viral illness to be acquired in Canada.
Here’s what you need to know about the virus, which also made headlines this year for infiltrating hundreds of dairy cattle herds in the United States.
What is avian flu?
Avian influenza, also known as bird flu, is a contagious viral infection that most often turns up in wild and farmed birds. There are several types, but all are members of the influenza A family. The version circulating in Canada is an H5N1 strain.
Most people who have caught bird flu since the first human infection was identified in Hong Kong in 1997 have been exposed for long periods to sick birds who shed the virus in their saliva and feces.
In humans, the receptors that avian influenza viruses lock on to are located deep in the lungs, which makes the pathogens harder to catch than seasonal flu viruses that target the upper respiratory tract. Human-to-human transmission of avian flu is exceedingly rare, and there is no evidence of sustained spread among people, according to the Public Health Agency of Canada.
The downside to those deep-lung receptors is that avian flu can cause dangerous lower-lung infections in humans. That’s part of the reason that about half of the approximately 900 human infections identified globally, most in Africa and Asia, have been fatal.
How is avian flu affecting birds and mammals?
A highly pathogenic version of H5N1 known as clade 2.3.4.4b has devastated wild and farmed birds across North and South America since it was first identified in a chicken on a Newfoundland farm in December, 2021.
The virus is so contagious and severe in birds that more than 11.7-million farmed birds, mostly chicken and turkeys, have died or been ordered destroyed by the Canadian Food Inspection Agency (CFIA) since 2022. There are currently 24 farms in B.C. with active infections, many of them in the Fraser Valley, where the infected teen lived.
H5N1 2.3.4.4b has also spilled over into mammals, sickening cows, bears, foxes, skunks, raccoons, cats and marine mammals, among others. It caused a mass mortality event in South American sea lions, killing at least 24,000 in Peru, Chile, Argentina, Uruguay, and Brazil in 2023.
“Some animals have absolutely been decimated by this,” said Fiona Brinkman, a professor of genomics and bioinformatics at Simon Fraser University who tracks the evolution of avian flu viruses. “When it hopped over to cattle, that was also really notable and surprising, because we have a lot more human contact with cattle than say, marine mammals.”
Has bird flu been found in Canadian cows? And is my milk safe to drink?
The short answers are no and yes. Bird flu has not been detected in any Canadian cows, despite the virus having spread to more nearly 500 dairy herds in the U.S. this year. The CFIA has tested 1,211 commercial pasteurized milk samples from across Canada and 391 samples of unpasteurized milk at processing plants for viral fragments that would point to undetected spread in cows. All the samples have been negative. Milk is safe to drink so long as it is pasteurized.
Are there vaccines for avian flu?
Yes, but they wouldn’t be available right away. Health Canada has authorized three pandemic flu vaccines as a precautionary measure, two of which were developed using an older H5N1 strain. Like seasonal flu shots, the pandemic jabs are produced in eggs and take three to six months to make.
Canada generally doesn’t stockpile pandemic flu vaccines because they only have a shelf life of two years. Instead, under deals with several domestic and international pharmaceutical companies, the manufacturing process would kick-start as soon as the World Health Organization declared an influenza pandemic.
Who is most at risk from avian flu?
People who work on poultry farms or who have sustained contact with sick, wild animals are most at risk of catching bird flu. But unless there is a major genetic change that makes the virus more easily transmissible to humans, even their risk is low, especially if they wear protective gear. The general public has even less to worry about.
One of the silver linings of the H5N1 outbreaks on cattle and poultry farms in the U.S. is that, so far at least, the 46 human cases linked to those farms have been mild.
But Matthew Miller, Canada Research Chair in viral pandemics and director of the Michael G. DeGroote Institute for Infectious Disease Research at McMaster University, said those few dozen cases may not tell us much about the potential severity of bird flu. Many have been bad cases of conjunctivitis, or pink eye, thought to be contracted when workers rub their eyes or work near the udders of infected cows, which have been found to have high viral loads.
“I’ve been banging this drum for ages because I do worry that we are underestimating the risk that the virus poses by virtue of a route of exposure that is relatively unnatural and would not reflect how this virus transmits, were it to become transmissible between humans,” Dr. Miller said.
Still, Dr. Miller, Dr. Brinkman and public officials in Ottawa and B.C. continue to stress that, in their current incarnation, avian flu viruses pose little to no risk to the average Canadian.
