Public-health officials in British Columbia declined to provide any new details Monday about their investigation into how a teen caught bird flu in the province, but experts said the first known case of a human acquiring H5 influenza in Canada should prompt increased vigilance against the potentially lethal virus.
Provincial Health Officer Bonnie Henry announced in a statement Saturday that a presumptive case of H5 influenza has been identified in a teen living in the Fraser Valley. No information has been released about the teen’s age or condition, beyond the fact that he or she is being treated at B.C. Children’s Hospital in Vancouver.
The Saturday statement said the source of the virus is “very likely to be an animal or bird,” and that no other human cases have been identified.
If the case originated on a farm, that farm is not a member of the BC Poultry Association, the group says. Spokesman Shawn Hall told The Globe and Mail Monday that he was not aware of any human cases of avian flu associated with any of the several hundred chicken, turkey, egg and broiler hatching egg farms the association represents.
The detection of a human case of avian flu caught in Canada, “is very significant,” said Matthew Miller, Canada Research Chair in viral pandemics and director of the Michael G. DeGroote Institute for Infectious Disease Research at McMaster University.
“I think it is especially worrying as we move into the human flu season,” he added. “Lots of people have been raising concern around the potential for re-assortment events, which can happen when a person or an animal is infected by two different flu viruses at the same time.”
For now, public-health officials in B.C. and in Ottawa say the risk to people who don’t work on farms or interact regularly with wild birds is low. Human-to-human transmission of bird flu is exceedingly rare and there has been no evidence of sustained transmission between people, the Public Health Agency of Canada said.
Still, when humans have caught bird flu in the past, it has been deadly. Of nearly 900 confirmed human cases of bird flu identified worldwide between 2003 and last spring, 52 per cent were fatal.
Dr. Miller and others are particularly concerned about how a highly pathogenic version of H5N1 known as clade 2.3.4.4b might evolve.
The strain has been wreaking havoc in the animal kingdom in North and South America since it was first identified in Newfoundland in late 2021. In Canada alone, more than 11.7-million farmed birds have died or been culled after the virus was detected on more than 400 farms, according to the Canadian Food Inspection Agency (CFIA). There are currently 24 active outbreaks of highly pathogenic avian flu on farms in B.C., many of them in the Fraser Valley.
The same version of avian flu has spread to bears, cats, foxes, raccoons, marine mammals and even a pet dog in Oshawa, Ont., that fell ill last year after chewing on an infected wild goose.
Most significantly, highly pathogenic bird flu has spread to dairy cattle in the United States. The virus has not been detected in cows in Canada, or in Canadian retail milk, which the CFIA has been testing for harmless traces of the virus. (U.S. milk found to contain viral fragments was found to be safe, thanks to pasteurization.)
B.C. officials have not said which strain of H5 made the teen sick. The National Microbiology Laboratory in Winnipeg is conducting confirmatory tests on samples from the teen presumed to be positive for bird flu.
In the U.S., 46 human cases of avian flu have been identified this year, nearly all of them connected to cattle or poultry. None has been fatal, according to the U.S. Centers for Disease Control and Prevention, and many have manifested as bad cases of pinkeye, potentially caused by farm workers rubbing their eyes or getting sprayed with contaminated raw milk.
The B.C. case is “certainly a red flag,” according to Samira Mubareka, an infectious disease physician and medical microbiologist at Toronto’s Sunnybrook Health Sciences Centre.
“The risk of severe disease is relatively unknown with this particular clade of the virus,” she said. Earlier versions of bird flu had high mortality rates in Asia, but so far mortality is low in the United States. It’s also unclear how this version of the virus might affect younger people like the teen in B.C., she added.
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, Health Canada said in a response to questions from The Globe in May. Canada generally doesn’t stockpile them because they only have a shelf life of two years.
Health Canada did not immediately respond to a request for an update on vaccination plans Monday.
There are other steps Canada could take to stay vigilant against bird flu in humans, said Rob Delatolla, a University of Ottawa professor of civil engineering and applied public health whose lab is planning to start testing wastewater in some Ontario communities for evidence of undetected spread of H5N1 in humans later this year.
“I think it’s very, very important to have a system in place … to detect spread as soon as possible,” he said.