This colorized electron microscope image released by the National Institute of Allergy and Infectious Diseases on March 26, shows avian influenza A H5N1 virus particles (yellow), grown in Madin-Darby Canine Kidney epithelial cells (blue).The Associated Press
The British Columbia teen who caught the first known case of bird flu in a person in Canada is in critical condition, and public health officials say they may never know where the adolescent picked up the virus.
The Fraser Valley teen does not live, work or have any connection to poultry farms, where a highly pathogenic version of avian flu has decimated flocks at 24 sites in B.C. since early October.
All the people and pets that the previously healthy teen is known to have spent time with recently – including cats, dogs and reptiles – have tested negative for avian flu, Provincial Health Officer Bonnie Henry told a news conference Tuesday.
“I must caution that there is a very real possibility we may not ever determine the source,” Dr. Henry said. “But at this point, we have a number of leads that we’re following, and we will be tracking down everyone, because this is such a rare event.”
Here’s what you need to know about avian flu
The teen was not in school immediately before or after he or she fell ill, Dr. Henry said. About three dozen of the teen’s contacts have been tested and offered the antiviral oseltamivir as a precautionary measure.
The teen, whose age and gender Dr. Henry declined to reveal, first fell sick on Nov. 2 with pink eye and respiratory symptoms. The adolescent visited a local emergency room and was sent home.
On Friday, Nov. 8, the teen was admitted to B.C. Children’s Hospital in Vancouver in respiratory distress and is now being treated in the intensive-care unit.
Tests conducted that night at a lab at the BC Centre for Disease Control found the teen had an H5 subtype of influenza A. The case is deemed a presumed positive until Canada’s National Microbiology Laboratory in Winnipeg conducts confirmatory testing, which Dr. Henry said is expected in the coming days.
In the meantime, she said it’s likely the teen is infected with the same highly pathogenic strain of H5N1 that has decimated wild and farmed birds across North and South America since it was first detected in Newfoundland in late 2021. The virus has spilled over into a wide range of mammals, including bears, foxes, raccoons, cats, dogs and marine mammals.
This year, it made the jump to dairy cattle in the United States, sparking fears that the virus might further evolve to spread more readily among humans. As it stands, human-to-human transmission of avian flu is exceedingly rare, and there has been no evidence of sustained human transmission.
H5N1 has been detected in nearly 500 dairy herds in the U.S. since March, and 46 workers on affected farms have tested positive for H5N1. The virus has not been found in Canadian cows.
Most of the human cases connected to U.S. dairy farms have been mild, with the most common symptom being a bad case of pink eye.
But as the B.C. teen’s case demonstrates, avian flu can also make people severely ill. Of more than 900 cases identified worldwide since the first known human infection was found in Hong Kong in 1997, about half have been fatal. A Canadian died of bird flu in 2014, but that person was infected on a trip to China.
Dr. Henry said experts are working to understand why the human cases arising on U.S. dairy farms seem to cause milder illness than previous bird-flu infections that occurred mostly in Southeast Asia. Part of the explanation is likely that mild cases of bird flu have been overlooked in the past.
Another possibility, Dr. Henry said, is that more of the cases in places such as Vietnam and Cambodia have been in children, who seem to have less robust immunity to H5 influenza than older adults, who likely built immunity to related strains of seasonal influenza A that circulated in their childhoods.
Canadians still face little risk from the current incarnation of H5N1, public-health officials in B.C. and Ottawa have reiterated this week.
But Dr. Henry said she and other experts worry the virus could mutate to spread more easily among humans. She pointed to the recent detection of highly pathogenic avian flu in an Oregon pig as a concerning development. Pigs, which have receptors for avian and human influenza, could serve as a mixing vessel for the new versions of the bird flu.
“So this is why it is incredibly important for us to investigate this really thoroughly, to understand if anybody else is infected and to try and understand the transmission and the exposure patterns here,” Dr. Henry said.