According to a recent study, the continuing avian influenza outbreak that started in late 2021 in Europe and the Americas has been characterized by quick genetic mutations and significantly enhanced pathogenicity in both birds and mammals.
The new strains of the H5N1 avian virus mutated quickly and got worse as it traveled over Europe and the Americas in the previous two years, according to the peer-reviewed study that was published in Nature Communications.
A growing number of mammals have been discovered to be infected with the virus in previous weeks, with mass extinctions of seals and sea lions recorded in Russia and in America, as well as the discovery of infection in dozens of foxes, skunks, dolphins, raccoons, cats, and other animals.
Corresponding author Richard Webby stated that “We haven’t seen a virus quite like this one. In 24 years of tracing this particular H5N1 flu lineage, we haven’t seen this ability to cause disease but also be maintained in these wild bird populations.”
Before reaching Canada and then moving on to the rest of the Americas, the virus acquired a new variation of the viral protein neuraminidase, which boosted its capacity to spread between birds.
Following its arrival in Canada, the virus immediately underwent another mutation, combining with other flu viruses to become better suited to the bird population, including species that were previously less susceptible to the flu.
The virus also got worse as it reached the Americas; in February 2022, samples of the virus were taken from an infected eagle and given to ferrets, which quickly lost weight, were lethargic, and had severe neurologic symptoms like paralysis and loss of muscular function.
Webby went on to say that “Some of these are really nasty viruses. 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.”
The scientists infected ferrets with viral samples they had later discovered during the epidemic as well. The study team observed that viral samples with a higher proportion of gene segments derived from North American lineages appeared to induce more severe sickness.
Webby emphasized that this circumstance is unexpected because the viruses’ capacity to cause serious illness changed with only a few events.
The researchers emphasized that although the virus’s increasing pathogenicity is “of major concern,” it has not yet evolved to transfer between humans effectively and currently poses little harm to people.
However, the researchers did point out that just a small number of amino acid alterations in a small number of flu proteins are required to allow for persistent human-to-human transmission.
“Overall, their risk to humans is still low. But that risk does seem to be changing, and these viruses are doing things that we haven’t seen H5s do before. They’ve come into the continent’s wild bird population, they’ve reassorted, and they’ve been maintained over time. There are now many different types out there, and they’re very nasty,” Webby said.
It would take “two or three slight alterations in one protein of the viruses,” according to Ian Brown, chief of virology at the UK’s Animal and Plant Health Agency, for the bird flu to become better suited to humans.
The H5N1 avian influenza pandemic that has been ongoing in Europe and the Americas since 2021 has been dubbed “the largest-ever” outbreak on both continents.
Both birds and animals have been severely impacted by the pandemic.
Over 58 million chickens have been afflicted in the US alone, and thousands of sick wild birds have been discovered in practically every state. Additionally, about 200 instances have been found in animals across the US.
In over 24 countries in Europe, tens of thousands of domestic and wild birds were confirmed to be sick, with many marine birds being impacted.
In the US, Cambodia, Ecuador, Chile, the UK, and the US, human instances have been found.
The H5N5 subtype of avian influenza was discovered by Canadian officials in a raccoon on Prince Edward Island in May. This was the first time the virus was ever found in a mammal.
In a pre-print study published in April, Canadian researchers discovered that a strain of H5N1 isolated from a red tailed hawk could spread successfully between ferrets, inflicting fatal sickness on the animals.
The findings of the study’s researchers suggested that the red-tailed hawk may have become infected by consuming mammalian carrion since the viral sample they obtained from the bird showed symptoms of adaptation to mammals.
Its increased transmissibility in ferrets may also have been caused by its transmission via several other species.
Since ferrets may get human influenza viruses and have symptoms that are comparable to those of humans, they are used as significant animal models for studying how viruses might impact people.
Although it has been demonstrated that H5N1 can occasionally result in a fatal sickness, previous research has indicated that it is typically not readily transferred between ferrets.