Canadian Scientists Keep Watchful Eye on H5N1 Human Case

Now that Canada has confirmed its first human case of highly pathogenic avian influenza (HPAI) linked to H5N1, virologists and infectious disease experts are urging caution around surveillance, infection control, and the potential for spread among mammals and humans.

The patient, a teenager in British Columbia, was hospitalized on November 8 and remains in critical condition with acute respiratory distress as of this writing. Public health officials at the National Microbiology Laboratory in Winnipeg, Manitoba, Canada, confirmed that the virus strain is related to the ones circulating among poultry in British Columbia.

So far, the case appears to be isolated, and no additional infections have been detected among the teen’s family, friends, or healthcare workers. But Canadian and American scientists who have studied the genetic sequence of the virus have found mutations that could make it easier to infect humans. Even if this strain remains contained after the teen’s case resolves, the mere fact that mutations have occurred could be a cause for concern about future strains.

“HPAI is one of those diseases that scientists, public health specialists, animal health specialists, and physicians have been watching closely for 20 years due to its epidemic and pandemic potential, including impacts to agriculture, food security, and financial security,” Isaac Bogoch, MD, associate professor of medicine at the University of Toronto and infectious disease specialist with the University Health Network, Toronto, Ontario, Canada, told Medscape Medical News.

“The last couple of years have been notable in that the H5N1 outbreak among wild birds and migratory birds has been larger, and the spillover to dairy cows and humans in the US is obviously concerning,” he said. “As we see more viral reassortment and more mammals are impacted, the more opportunities there are for this to go awry.”

Current H5N1 Outlook

Canadian public health officials and virologists are still unsure how the teen in British Columbia became infected, Bogoch said. The case has prompted concern due to the disease severity and need for hospitalization, while other cases across North America have remained mild.

The United States has reported 53 human cases as of November 21, according to the Centers for Disease Control and Prevention. In all but one case, the infections occurred among dairy or poultry workers, primarily in California, Colorado, and Washington. In all these cases, patients have reported mild symptoms, including mild respiratory issues and conjunctivitis. None have been hospitalized.

In Canada, the teen was infected with a strain of the virus circulating in wild birds. This strain has also been found in poultry outbreaks in British Columbia and Washington during the past month. So far, the risk for infection remains low for the public, according to the Public Health Agency of Canada.

“This detection was picked up via hospital-based influenza surveillance, confirming that human influenza surveillance in British Columbia and Canada is effective at detecting avian influenza A (H5N1),” Theresa Tam, MD, Canada’s chief public health officer, said in a statement. “We must continue to remain vigilant in our efforts to prevent the spread of avian influenza between animals and to humans.”

For now, Canadian virologists are watching developments closely and urging caution among those who encounter wild or migratory birds but not recommending major changes overall.

“The fact that we have a first human case in Canada is not at all surprising, given what is happening in the US and Europe, as well as what is happening in domestic bird flocks in British Columbia,” said Brian Ward, MD, professor of medicine at McGill University, researcher with McGill’s J.D. MacLean Centre for Tropical Diseases, and co-director of McGill’s Vaccine Study Centre, Montreal, Quebec, Canada.

“Millions of migratory waterfowl are flying over Canada right now, many of which may be carrying or infected with the virus,” he said. “The bottom line is that increasing evidence of mammal-to-mammal spread among dairy cows, elephant seals, and mink and ermine farms is worrisome, but we don’t need to sound the sirens yet.”

Future Outbreak Measures

Looking ahead, though, the developing situation feels more threatening than benign, given the ongoing spread among dairy cattle in the United States, said Bogoch. “It’s difficult to get the genie back in the bottle. I had hoped to see the cases slow down this year, but we just haven’t seen that.”

The fact that surveillance measures such as wastewater sampling have been scaled back in some areas of Canada is cause for concern, Bogoch added.

“We have great foundations for surveillance and action; we just need to make sure they are supported adequately, that groups communicate (across too many silos), and that there are quick responses,” said Scott Weese, DVM, professor of pathobiology at the Ontario Veterinary College and director of the University of Guelph’s Centre for Public Health and Zoonoses in Guelph, Ontario, Canada.

“With cattle in the US, I think it’s highlighted what can happen if the initial response is not very aggressive. There could have been a lot more proactive response to H5N1 in dairy cattle, but there are so many competing interests and unwillingness to take necessary steps that the virus continues to spread,” he said. “Hopefully we’ve learned from that. However, as is often the case, the science is sometimes the easy part. Getting people to take the required actions is the challenge.”

On a personal level, masks and social distancing work well against influenza virus, including both seasonal and avian strains, said Ward. On a broader level, healthcare providers can monitor patients and support testing, where appropriate.

“The most important thing for people to know is that there is going to be another pandemic. It might or might not be due to a variant of H5N1, but it will come at some time,” said Allison McGeer, MD, professor of laboratory medicine and pathobiology at the University of Toronto and an infectious disease specialist with the Sinai Health System, Toronto, Ontario, Canada.

Healthcare providers should follow ongoing updates to public health guidance, support surveillance where possible, and work with hospital leadership and infection control officials to ensure that pandemic plans are in place, she said.

“They may not be needed in the next few months, but they will be needed,” McGeer said. “We know a lot more about influenza than we did about SARS-CoV-2, so we have more tools to mitigate the impact, but we need to have them ready and know how to use them effectively.”

Carolyn Crist is a health and medical journalist who reports on the latest studies for Medscape Medical News, MDedge, and WebMD.