July 13, 2023
When avian influenza (also known as bird flu) is featured in the news, it is often accompanied by alarming headlines highlighting the highly infectious nature of some strains and their ability to cause severe disease. The current outbreak of the H5N1 strain of highly pathogenic avian influenza (HPAI) virus has garnered more headlines globally, documenting its spread around the world killing scores of domestic and wild birds. H5N1 has also spread into mammals causing fatal infections in skunks, foxes, raccoons and stray cats.
The spread of H5N1 has raised concerns that the virus might continue to evolve to the point where human-to-human transmission could happen, potentially leading to outbreaks or a pandemic.
Although the risk to people remains low, scientists at the Public Health Agency of Canada’s (PHAC) National Microbiology Laboratory (NML) and partners, are closely tracking and monitoring the strains of H5N1 in Canadian wildlife. They are working to inform public health decision making and to better understand the evolution of the virus and its risk to people in Canada and around the world. Scientists are also studying H5N1 to help guide the development of tests, vaccines and treatments.
What is avian influenza?
Avian influenza is a type of flu found in birds and some strains of the virus can infect mammals, including humans. Human cases of avian influenza are rare and no domestically acquired human cases have been reported in Canada. Cases of avian influenza that have occurred in humans around the world have been as a result of direct contact with infected birds, mostly on farms. Unfortunately, the human fatality rates can be very high – over 50% with some strains of avian influenza, including H5N1.
Study shows H5N1 is increasing its ability to transmit between mammals
Scientists from the NML, along with scientists from the Canadian Food Inspection Agency’s (CFIA) National Centre for Foreign Animal Disease (NCFAD) and Sunnybrook Research Institute, recently completed a study in animal models on the severity and transmissibility of four H5N1 strains circulating in Canada. The NML and NCFAD are co-located at the Canadian Centre for Human and Animal Health in Winnipeg and both have high containment laboratories.
Dr. Darwyn Kobasa, a Senior Research Scientist at the NML, is an expert on influenza research and studying high consequence viruses such as avian influenza.
“One of the most important aspects of our role in public health is to provide early warnings about what might be happening,” says Dr. Kobasa. “It is important to be vigilant about these emerging trends, so we study how the virus is transmitted to provide some indication of how high the risk of transmission to people is.”
For this specific study, selected samples that tested positive for H5N1, from domestic and wild animals across Canada, were sent to the NCFAD for testing. They looked for markers in the samples that indicate the virus is adapting in ways that make it more likely to infect mammals.
“This collaborative study helps us to better understand how the virus changes and evolves after the spill-over from avian species to mammals,” says Dr. Yohannes Berhane, the Head of the CFIA’s Avian Diseases Unit at the NCFAD. “Some strains have already developed changes in their genome that give them an advantage to replicate in mammalian cells and spread more easily between animals. This gives scientists and public health experts clues about how to better mitigate the risks associated with the virus, and how to focus future research.”
After being tested at the NCFAD, the samples were then sent to the NML to assess the pandemic risk that these viruses might pose, by conducting further risk assessment studies in various laboratory animal models. The aim of these studies was to see how easily H5N1 can replicate in human airway cells as well as to assess the potential transmissibility of the virus through lab animals, such as ferrets. Ferrets are preferred as their respiratory systems best mimic those of humans; thus, influenza viruses show a similar progression of infection as seen in people. Researchers found that one of the strains of H5N1 studied spread easily by direct contact from mammal-to-mammal and caused severe disease in ferrets. This is the first research study showing mammal-to-mammal transmission in a laboratory setting.
“This experimental model of transmission shows the virus is increasing its ability to transmit efficiently between mammals,” says Dr. Kobasa.
One of the strains collected from a red-tailed hawk in Ontario was found to be particularly virulent and transmissible meaning it caused severe disease and spread easily to cage mates. More research will be required to understand this type of transmission in real-life settings. The study also examined the possibility of airborne transmission; however, the results were inconclusive.
While the findings of the study are noteworthy and merit heightened vigilance, the risk to the public remains low. One group of people who may be at increased risk of infection are those who are in close contact with infected birds or mammals and their environments.
Monitoring and pandemic planning
The NML has ongoing projects to evaluate whether known and novel vaccines and antiviral drugs can prevent and treat H5N1. They are also working with academic partners to test potential vaccines and treatments.
The NML and the CFIA will continue to work together to analyze samples and monitor how the virus is behaving in the wild and with domestic poultry and other animals. “We have developed complementary approaches to public health problems such as this one. Being in the same building and having established working relationships allows us to respond quickly and efficiently,” says Dr. Kobasa.
The situation in Canada and world-wide is dynamic, and scientists will continue to follow changes in H5N1, as it continues to evolve. “The global scientific community knows how important this work is and the difference it can make in being prepared for something that might happen,” says Dr. Kobasa.