The avian flu virus that is killing millions of animals worldwide has been found to spread ‘efficiently’ among ferrets in a laboratory, raising concerns about whether the virus could pass to humans.
In a new preprint, scientists in Canada have shown that H5N1 samples taken from a red-tailed hawk spread efficiently among ferrets, the main ‘animal model’ used by scientists in experiments to analyze how respiratory viruses can an impact on people.
It is the first study to clearly confirm that the virus can spread from mammal to mammal, although recent deaths of many animals, including sea lions, have previously suggested this. Analysis of an outbreak in a mink farm in Spain and in seals in New England also indicated mammalian spread.
But the findings from Canada suggest that some H5N1 strains with “some adaptations that allow for a higher degree of replication, pathogenicity and transmission” could be spreading.
Over the past 18 months, bird flu has devastated wild and farmed bird populations around the world. But there has also been growing alarm over cases in mammals including foxes, sea lions, dolphins and even domestic cats.
This has created unprecedented opportunities for the virus to move and reassort, a process where different strains of the same pathogen combine into something new.
“The risk [for humans] it’s increasing, meaning there’s a lot of virus in poultry and wild birds,” Professor Munir Iqbal, a member of the UK government’s modeling group for avian flu, recently told the Telegraph.
“The virus can change at any moment, and therefore the risk is greater when there is more of it in the environment. This does not mean [a human epidemic] it’s imminent… but no one is in control of the virus,” he said.
‘We have to be alert’
So far, cases in people have been sporadic and health agencies have kept the threat low.
But the latest study points to the “potential for this virus to infect and transmit among mammals, including humans,” according to researchers from organizations including the Public Health Agency of Canada.
Professor Marion Koopmans, a Dutch virologist who was not involved in the research, said the preprint, which has yet to be peer-reviewed, was a reminder of the threat posed when combining slightly different H5N1 strains.
“[The] The more important message here is: Let’s not assume we know “the” properties of the viruses that are spreading so widely,” he told the Telegraph on Monday.
“With widespread spread among wild birds, we see mixtures of viruses arising, where some of the internal genes are derived from other avian influenza viruses. This can happen if you see co-infections of cells in one individual (bird) with two viruses.
He added: “We have also seen this happen in Asia and Europe. What the study adds is that this evolution can lead to strains with very different traits. In this case, it’s about gravity and transmission capacity in an animal model. There’s no airborne evidence that would raise a large flag, but it’s not very comforting either.
“To me it says: We really need to stay alert and improve our surveillance, even in mammals like mink and pigs.”
The Chilean case shows adaptation
The latest preprint comes after a sample taken from a Chilean man who contracted H5N1 last month had two genetic mutations that indicate mammalian adaptation, according to the US Centers for Disease Control and Prevention.
The gene, called PB2, has previously been shown to help the virus replicate within – and thus spread between – mammals.
Yet the scientists pointed out that previous studies, including in ferrets, have concluded that H5N1 needs to undergo more changes to effectively spread to humans on a large scale.
“There are three main categories of changes that we think H5 needs to go through to go from being an avian virus to being a human virus,” Richard J. Webby, a bird flu expert at St. Jude’s, told the New York Times. Children’s Research Hospital. .
“The sequences of the person in Chile have one of those classes of changes. But we also know that of these three sets of changes, this is the easiest for the virus to make.”
If such changes occur, the results could be harmful, which is why experts including Sir Jeremy Farrar, the World Health Organization’s principal scientist, have urged governments to urgently step up efforts to develop human flu vaccines flu.
“Because there is little or no H5-specific immunity at the population level, if an H5N1 isolate capable of sustained transmission were to cause a species jump in humans, this would likely represent a destructive infection in the immunologically naïve population,” Canadian scientists warned.
Professor Ian Brown, director of scientific services at the UK’s Animal and Plant Health Agency, who was not involved in the study, added the findings were ‘important but not entirely unexpected’.
“The study did not unequivocally demonstrate airborne transmission which could be important in a mammalian context if sustained population-level transmission were to occur,” he said. “The work highlights the importance of sharing global intelligence to track and monitor these viruses as they spread more widely and potentially across species.”
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