Avian influenza in birds worldwide is changing rapidly, and the surging number of cases seen in mammals is cause for concern.
Since first emerging in 1996, the H5N1 avian influenza virus had previously been confined to primarily seasonal outbreaks. Starting in 2005, experts began identifying key events – like new clades, new species being infected, and the spread to new areas – as the avian flu virus gained greater virulence.
While the risk to humans still remains low, according to the Centers for Disease Control and Prevention (CDC), something happened in mid-2021 that made the group of viruses much more infectious, according to Richard Webby, the head of a World Health Organization collaborating center studying influenza in animals.
During 2020, reassortment (gene-swapping) between poultry and wild bird viruses led to the emergence of HPAI H5N1 with the NA viruses with an N1 NA from wild birds. It quickly spread across Europe and into Africa, the Middle East and Asia.
By October-November 2020, the HPAI H5N8 virus was detected in several swans, seals, and a fox in the United Kingdom. Human infections, while few and far between were mild, and the result of exposure to backyard poultry.
Since then, outbreaks have lasted all year round, spreading globally to new areas and leading to mass deaths among wild birds and tens of millions of poultry being culled.
Webby, who is also a researcher at St Jude Children’s Research Hospital in the US city of Memphis, said the avian flu outbreak of 2021 was “absolutely” the largest outbreak of avian influenza the world had seen.
He led research, published this week in the journal Nature Communications, showing how the virus rapidly evolved as it spread from Europe into North America.
According to Live Science, when the scientists tested the newer avian flu strains for their ability to cause disease in mammals by infecting a ferret model, they found an unexpectedly high amount of pathogenicity.
“Some of these are really nasty viruses,” Webby said. “There’s a huge amount of the virus in the brain of infected animals. That’s the hallmark of what we saw with these flu strains — increased pathogenicity associated with high virus load in the brain. That’s not the first time we’ve seen H5 viruses in the brain, but these are probably some of the most virulent we’ve looked at over 24 years of following these viruses.”
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The biggest takeaway from this study is that while the risk is still low for humans, the virus is not remaining static. “That does increase the potential that even just by chance” the virus could “pick up genetic traits that allow it to be more of a human virus,” Webby said.
“This is not just a chicken virus now,” Webby said. “It’s also infecting other avian and mammal species in the U.S. It’s a higher exposure risk for humans and other mammals than we’ve ever had in North America. We’ve never really been exposed to this level of circulation of these highly pathogenic flu viruses.”
Here is a good piece of advice: Even though the risk of spreading infection is low, the research suggests humans should be cautious interacting with wildlife.
