A Canadian teenager who is in critical condition after contracting the H5N1 bird flu was infected with a version of the virus different from the one circulating among dairy cattle in the United States, Canadian authorities announced Wednesday.
The National Microbiology Laboratory in Winnipeg confirmed that the infection was indeed caused by the H5N1 virus. But genetic sequencing has shown that it is a genotype found in wild birds, and not the version circulating in dairy cattle in the US.
Canada is conducting surveillance on dairy cows looking for the virus, but has not found it in any herd so far.
Bonnie Henry, British Columbia’s provincial health officer, told STAT in an interview that she had expected these results from genetic sequencing. “That’s what we see consistently,” she said.
The unidentified teen lives in British Columbia.
The H5N1 virus has evolved into a variety of strains in the nearly thirty years it has been circulating worldwide. The version spreading among cows is known as a 2.3.4.4b virus, of a genotype called D3.13. There have been about 46 human cases confirmed in the US this year, all involving very mild disease.
Historically, H5N1 has been associated with serious illness. Of the approximately 950 human cases recorded so far, just under half have died.
The virus that infected the Canadian teenager was a 2.3.4.4b virus of the D1.1 genotype. This version of the virus, spread by wild birds, has caused poultry outbreaks in several places, including recently in Washington state.
British Columbia currently has 26 H5N1 outbreaks at poultry farms, many of which are in the Fraser Valley in the southwestern part of the province. The infected teenager lives in that part of the province.
This individual is the first confirmed person to have contracted H5N1 in Canada. In 2014, a person in the neighboring province of Alberta was diagnosed with H5N1, but that person had recently returned to Canada from China and was believed to have been infected there. That earlier H5N1 case was fatal.
Health officials in British Columbia have so far been unable to determine how the teen contracted bird flu. He or she is too ill to answer questions, but information from family members indicates there was no exposure to infected poultry, Henry said. The teenager had contact with a number of pets – cats, dogs and reptiles – both at home and with friends. But none of those animals tested positive for the virus.
During a news conference Tuesday, Henry warned that as long as the search for the source of the infection continues, it may never be known how the teenager contracted the virus. STAT asked if this was an attempt to be cautious or an attempt to raise expectations. “A little bit of both,” Henry said.
However, comparing the genetic sequence of the teenager’s virus with that of known H5N1 outbreaks in poultry could provide further clues, she said. “I’m more confident today than I was yesterday that we might actually find it.” [source]but maybe not.”
The existence of an unexplained H5N1 case is troubling to experts who monitor this virus, which has been high on the list of possible pandemic flu viruses for years. Such a case could be a one-off, such as the recent unexplained case in Missouri, in a person with no known exposure to cows, wild birds or poultry. But also early in the 2009 A1N1 flu pandemic, two sporadic cases of swine flu infection in children in California who had had no contact with pigs or each other were the first signs that a pandemic had begun.
Henry is aware of both scenarios. “Obviously my senses went off when we first heard about this,” she said. ‘But I feel more confident that we have followed up with everyone they had close contact with during the… contagious period. We haven’t found anyone else who is sick. And we are testing.”
“So I feel more confident that it was a single exposure and a rarer event. … More cases would have come to light by now if this was an exposure event where multiple people were exposed, or if there had been person-to-person transmission, which we know is rare with H5N1.”
Allison McGeer, an infectious disease consultant at Toronto’s Sinai Health, and a professor at the University of Toronto, shares Henry’s optimism that this may be a once-in-a-lifetime event.
“You would think that if this was the start of something, we would have seen other cases by now,” McGeer said. “Any day we don’t hear from BC is a good day.”
Henry said British Columbia is taking blood samples from people who had close contact with the teen to see if antibodies against the virus had been developed. But doing that kind of work will take some time, because it takes about two weeks for people to develop antibodies against a pathogen after exposure. She suggested some results could be available next week.