Canada’s First H5N1 Human Infection Linked to D1.1 Genotype, Not the D3.13 Variant Found in American Cows

Medical News: In a recent case raising both alarm and questions, Canadian health authorities have confirmed that a teenager in British Columbia has contracted H5N1 avian influenza, commonly known as bird flu. This case is Canada’s first instance of human infection with the H5N1 virus, marking a milestone in the country’s battle against avian diseases. However, genetic sequencing has revealed an unexpected twist: the teenager’s infection was caused by the D1.1 genotype strain, which is primarily found in wild birds, rather than the D3.13 variant currently circulating in U.S. dairy cattle.


Canada’s First H5N1 Human Infection Linked to D1.1 Genotype,
Not the D3.13 Variant Found in American Cows

The individual, whose identity remains undisclosed for privacy reasons, is reportedly in critical condition and is currently in ICU. This Medical News report delves into the unique aspects of this case, including the investigation into its origins and potential implications for public health. According to the National Microbiology Laboratory in Winnipeg, the findings underscore the complexity of H5N1’s evolution and its multiple genotypes. While Canada has been actively monitoring its dairy herds for avian influenza, no cases have been reported in livestock to date, in contrast to the U.S., where the D3.13 variant has appeared in cows, with cases reportedly affecting humans but causing only mild illness.
 
A New Strain in an Old Threat
Bird flu is no stranger to the scientific community, having circulated globally for nearly three decades. The H5N1 virus has since evolved into various genotypes, leading to different levels of transmissibility and virulence. The genotype D3.13, primarily identified in American cattle, is responsible for mild human cases. The version that affected the Canadian teenager, however, belongs to the D1.1 genotype - a lineage more commonly associated with wild birds and known to have caused outbreaks among poultry in many Canadian regions.
 
Health experts are closely analyzing this case because D1.1 has shown a tendency to cause severe illness in humans. With over 950 recorded human infections worldwide, nearly half have led to fatalities. The British Columbia teenager’s case has raised red flags among health authorities, as this is only the second confirmed H5N1 case in Canada, the previous one occurring in Alberta in 2014, linked to a traveler returning from China who later succumbed to the virus.
 
The Mystery of Transmission: A Source Yet to Be Determined
British Columbia’s Provincial Health Officer, Dr. Bonnie Henry, has indicated that health authorities are currently investigating the source of the infection, but finding an answer has been challenging. Dr. Henry confirmed that the teenager, who lives in British Columbia’s Fraser Valley - a region with 26 active H5N1 outbreaks in poultry farms - had not been in direct contact with infected poultry. Despite efforts to gather information from family and friends, the patient remains too ill to communicate effectively, c omplicating efforts to pinpoint potential exposure routes.
 
Family members report the teenager had close interactions with pets, including dogs, cats, and reptiles, which led experts to conduct tests on these animals. However, none of them showed signs of infection. During a press conference, Dr. Henry cautioned the public that the source of the virus might remain unknown, emphasizing the challenges inherent in tracking zoonotic diseases, which often have elusive transmission pathways. Yet, some officials hold out hope that further genetic testing might reveal new insights, potentially linking the infection to local bird populations.
 
Concerns for Pandemic Potential in Unexplained Cases
The discovery of an H5N1 infection without a known source of exposure raises concerns about a potential shift in the virus’s behavior. While it is possible this is an isolated case, health experts are mindful of the threat H5N1 poses as a pandemic flu candidate. Unexplained cases of H5N1 are unsettling, as they can indicate silent transmission routes or unforeseen mutations. This event is eerily reminiscent of the early days of the 2009 H1N1 pandemic when isolated cases of swine flu signaled the beginning of widespread human transmission.
 
Dr. Henry expressed cautious optimism, noting that thorough testing of the teenager’s contacts has so far shown no additional cases. Close contacts are also being tested for antibodies, which might indicate asymptomatic or mild infections.
 
Genetic Analysis Offers Clues, But Questions Remain
The key to understanding this H5N1 infection may lie in its genetic makeup. Dr. Henry and her team are currently conducting genetic sequencing on the virus isolated from the teenager to compare it with strains found in regional poultry outbreaks. The H5N1 virus, while typically transmissible between birds, poses a significant threat if it adapts to spread among humans. Genetic differences between the Canadian and U.S. strains further highlight H5N1’s ability to diversify, which may contribute to both increased transmissibility and the virus’s persistence in various host species.
 
The teenager’s infection by the D1.1 genotype - distinct from the D3.13 variant in American cattle - suggests that wild bird populations remain a significant reservoir for H5N1.
https://www.canada.ca/en/public-health/news/2024/11/update-on-avian-influenza-and-risk-to-canadians.html
 
Canada has not observed D3.13 infections in domestic animals, underscoring the localized patterns of virus genotypes. Scientists warn that the ever-evolving nature of avian flu strains like H5N1 necessitates ongoing vigilance, especially as the virus’s presence in wild birds and poultry increases the chances of human exposure.
 
Managing Public Health Risks
Although health authorities consider the risk to the general public to be low, they are nonetheless implementing preventive measures. Dr. Henry advises that Canadians avoid handling sick or dead birds and report any unusual bird or animal behavior. Health officials are working closely with provincial and federal agencies to monitor H5N1’s presence in both wildlife and domestic animals to detect any potential shifts in transmission patterns. As scientists continue to track H5N1’s spread and evolution, maintaining robust surveillance and preparedness will be essential.
 
In addition to the teenager’s case, authorities are investigating several other potential avian flu exposures across British Columbia. Those in contact with poultry workers are being advised to take additional precautions to avoid infection, including wearing protective gear when handling birds and practicing rigorous hygiene measures.
 
Conclusion: A Cautionary Case for Pandemic Preparedness
The teenager’s H5N1 infection serves as a reminder of the unpredictable nature of avian influenza and the need for ongoing vigilance. While the case appears isolated, the possibility that H5N1 could evolve into a more transmissible strain among humans cannot be entirely dismissed. Public health experts emphasize the importance of continued monitoring, rapid testing, and international cooperation to mitigate the risks posed by avian influenza. As long as H5N1 circulates among wild birds and livestock, the potential for zoonotic transmission remains.
 
This case highlights how even a single infection can provide critical insights into a virus’s behavior, guiding public health efforts to control potential outbreaks. With scientists and health officials working tirelessly to study H5N1’s characteristics, Canadians are encouraged to stay informed and exercise caution around potentially infected animals.
 
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Read Also:
https://www.thailandmedical.news/news/reassorted-strain-of-h5n1-bird-flu-virus-discovered-in-cambodia
 
https://www.thailandmedical.news/news/u-s-cdc-now-reports-that-7-percent-of-tested-dairy-farmworkers-were-possibly-infected-with-the-h5n1-virus
 
https://www.thailandmedical.news/news/first-human-case-of-h5n1-bird-flu-detected-in-canada