What we know about H5N1 avian flu and the risk to humans

Over the last few months, Canadians have been hearing about the spread of H5N1 avian flu as it takes an enormous toll on poultry farms across the country. It’s a virus that has also gained a global foothold. The World Health Organization says although H5N1 has “spread widely in wild birds and poultry for 25 years,” there are now several international reports of spillover infections to mammals—including minks, otters, foxes and sea lions. That has sparked concerns that humans could be next and the WHO is urging countries to “strengthen surveillance in settings where humans and farmed or wild animals interact.” “For the moment, WHO assesses the risk to humans as low, Dr. Tedros Adhanom Ghebreyesus, the organization’s director-general, said at a news briefing on Feb. 8. “Since H5N1 first emerged in 1996 we have only seen rare and non-sustained transmission of H5N1 to and between humans, but we cannot assume that will remain the case and we must prepare for any change in the status quo.” Dr. Syra Madad, an infectious disease epidemiologist at the Harvard Kennedy Belfer Center for Science and International Affairs in Cambridge, Mass, agrees. “I don’t think there’s a need to cause a significant alarm, but it’s a time to be cautious,” Dr. Madad said. “When you talk about a highly pathogenic avian influenza virus . . . it’s something to take seriously,” she said. “It’s something where we need to ensure that we are preparing for the potential of human cases.” What is H5N1? H5N1 is a large family of Influenza A viruses, said Dr. Shayan Sharif, acting dean of the Ontario Veterinary College at the University of Guelph. Some are highly pathogenic and some have low pathogenicity—meaning the capacity to kill or severely sicken birds. The concern right now centres on the highly pathogenic H5N1 circulating worldwide. It’s called “avian flu” or “bird flu” because it has mainly infected birds. Why are we hearing about H5N1 now? “Unfortunately it seems that the virus is gaining a little bit more momentum in terms of what it has done so far and what we are predicting it could be doing in the next short while,” Sharif said. “Over the last several months or so it’s been going all around the globe,” he said. “It has criss-crossed our country a couple of times over.” He’s concerned about both the multiple cases of mammal infections around the world and the implications that has for the virus spreading widely to humans. “When you have mammals dying of a highly pathogenic avian influenza virus, it’s not a good sign. It is a sign that I would take very seriously, extremely seriously.” In Canada, there have been some “one-off” transmissions to non-avian animals, including mammals, Sharif said, but there has been no sign of mammal-to-mammal transmission in this country. Has H5N1 spread to humans? Yes—but human cases are “quite rare” and have happened when people were directly exposed to infected animals, the WHO says. Worldwide, humans have rarely transmitted the virus to another human “unless they have very, very close contact or a very specific condition for transmission,” Dr. Sylvie Briand, WHO’s director for epidemic and pandemic preparedness and prevention, said at the Feb. 8 news briefing. In Canada, there was one “travel-related” human case reported in early 2014, the Public Health Agency of Canada said in an email on Friday. “It was the first and only H5N1 case reported in Canada to date,” the email said. How sick do humans get with H5N1? H5N1 is “not very transmissible” between humans because it’s a “zoonotic virus and therefore the virus is very adapted to animals and not to humans,” Briand said. But when humans have been infected, “they are more likely to have severe disease,” she said, and people have died 30% to 50% of the time. There were a total of about 860 reported human cases of H5N1 around the world between 2003 and 2021, said Dr. Madad. Although the fatality rate seems scary, she cautions that “we just don’t know” if that rate is accurate because most cases were likely identified when the patient was sick enough to be hospitalized. That means many non-fatal cases could have been missed because they were never tested, Dr. Madad said, and there may have been people who were asymptomatic. What are the symptoms for humans? “People who become infected with avian influenza (H5N1) can become seriously ill quickly,” says an information page on the Public Health Agency of Canada’s website. Symptoms begin like other flu illnesses and can include high fever, cough, aching muscles and sore throat. Other possible symptoms include stomach pain, chest pain and diarrhea. “The infection may progress quickly to: severe respiratory illness, which can include difficulty breathing; pneumonia; Acute Respiratory Distress Syndrome; (and/or) neurologic changes (changed mental state or seizures),” the webpage says. How can people protect themselves? The people at risk right now are those who have close contact with birds, said Dr. Madad, whether they work on a commercial farm, keep chickens in their backyards or interact with wild birds. “It’s important that they understand that there is obviously a very large outbreak happening,” she said. “If they come across a sick bird, they should be very cautious.” The Public Health Agency of Canada recommends that people wear personal protective equipment including a mask, gloves, goggles and boots. They should also avoid touching their mouth, nose or eyes before thoroughly washing their hands, Dr. Madad said People should consider taking those precautions whenever they handle birds, even if none of them appear to be ill, she suggested. When it comes to birds out in the wild, “members of the public should not handle sick or dead wild birds or other wildlife,” the Public Health Agency of Canada website says. “Pets should also be kept away from sick or dead wildlife.”

What we know about H5N1 avian flu and the risk to humans

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