Photo: Fred Tanneau/AFP/Getty Images
Multiple waves of avian flu have left a trail of devastation around the world, killing and culling more than 300 million chickens, ducks and geese and an unknown number of wild birds between 2005 and 2021.
Today, in the midst of the worst outbreak recorded in parts of Europe and North America, a global group of researchers is keeping a cautious watch amid concerns over the impact of the disease on humans.
“There are concerns that it has pandemic potential,” says Wendy Blay Puryear, a molecular virologist at Tufts University. “Before Covid got on anyone’s radar, that’s what we all followed closely.”
The virus is currently considered low risk for humans, he says. “But anything that has the ability to multiply and evolve rapidly, and anything that has the ability to infect many different hosts is a borrowed time.”
Much of the focus of experts is on H5N1, a highly pathogenic avian flu that is partially fueling the worldwide increase in cases. First identified in 1996 at a goose farm in Guangdong, China, the virus has appeared in at least 63 wild bird species and has shown it can infect mammals such as bobcats, harbor seals and bears.
If it has settled in wild birds, it is much more complicated to control it and predict where it will go next.
Nichola J Hill, University of Massachusetts
Thijs Kuiken, a professor in the department of virology at Erasmus University Medical Center in Rotterdam, says the more the virus spreads, the more likely it is to spread to humans. There is concern that once the virus infects humans, it may become more adaptable to allow for human-to-human transmission.
“The chance of this happening is very low, but the impact – if it does – is huge, because that means we have a new flu epidemic at that time,” he says, pointing to the 1918 flu. As many as 50 million people associated with bird flu, as an example of an emerging avian pandemic.
As H5N1 traveled around the world, its impact on humans triggered alarms; Between 2003 and October 2022, the virus appeared in 865 people in 21 countries, resulting in 456 deaths. While most cases in Africa and Asia are linked to the handling of infected live poultry rather than human-to-human transmission, the figures show that the virus “has a high case fatality rate among infected individuals.” queen
Public health officials take little risk. In the UK, where a duck breeder tested positive for the virus after dealing with infected poultry in late 2021, the Health Safety Agency is working to develop a “ready exercise” to prepare people for an outbreak of avian flu, UKHSA an email to the Guardian with said.
In the Canadian province of British Columbia, public health officials recently warned doctors to be on the lookout for bird flu infections among patients after a spike in cases among poultry on local farms.
Ian Barr, deputy director of WHO’s Influenza Reference and Research Collaboration Center in Melbourne, says it will likely need more than one or two changes to enable human-to-human transmission of the virus.
“We’ll never know for sure about these viruses… but they’ve been with us in various forms for 18 years and they haven’t yet acquired the function of being easily transmitted to humans,” says Barr. “So, I hope the virus finds something difficult to do, but that’s something we’re not entirely aware of.”
He described it as a numbers game. “The more viruses out there, the more species they infect, the longer they stay around, the greater the chance that something will mutate, go wrong, or reappear with an unintended consequence.”
Rebecca Poulson of the University of Georgia College of Veterinary Medicine says efforts to stop the spread of this virus strain are complicated by its prevalence in wild birds.
“We know that birds travel incredibly long distances,” he says. “And if these birds are infected and shed these viruses as they move across the landscape, they can spread it quite far and wide in a really short period of time.”
Related: Bird flu ‘an urgent warning to move away from factory farming’
Nichola J Hill, a professor of biology at the University of Massachusetts in Boston, says the presence of the virus in wild birds and farmed poultry allows it to ping-pong among populations and increase its spread.
“I think we used to clung to the idea that we could control the virus in poultry, we’re ready, that’s fine,” he says. “And now we’re facing a new era because if it’s become established in wild birds, it’s much more complicated to figure out how to control it and predict where it will go next.”
What is clear, however, is the role our food system has played in getting us to this point, he says, referring to the high poultry density seen in commercial farming and the genetic similarity of most animals. “All of this corresponds to a state ripe for the virus to get a foothold and then evolve towards lethality.”