How worried should we be about avian flu?
This morning, the world woke up to some unsettling news. According to the UK Health Security Agency (UKHSA), the H5N1 “bird flu” virus – a lethal pathogen which has killed hundreds of millions of birds around the world – has turned up in mammals, including foxes and otters in Britain.
As is traditional on these shores, public health experts of the “keep calm and carry on” persuasion were quick to hit the airwaves to reassure us. “The risk of influenza A [H5N1] infection to UK residents within the UK is very low,” said official government guidance issued by the UKHSA. Only if someone you rub shoulders with caught it – “a confirmed contact” – would seven days’ medical observation be warranted, together with “urgent investigation of any new febrile or respiratory illness”.
If you feel a sense of déjà vu descending, you are not alone. We have not yet been asked to sing “Happy Birthday” twice while washing our hands, but large parts of Norfolk and Lincolnshire have been sealed off where outbreaks in poultry have been confirmed. A deadly virus jumping from one species to another is never good news. Remember when a not dissimilar H1N1 avian virus jumped from birds to swine in 2008-9, for example.
So what is the real risk here? What do the latest findings mean and how likely is it that this new strain of avian H5N1 could start to spread in humans?
The good news is that the virus has been doing the rounds for a long while in birds without mutating to spread efficiently in humans. It was first reported in the Far East almost 20 years ago and has spread to become common in farmed poultry and wild birds around the world.
“From 2003 until Nov 25 2022, 868 confirmed human cases and 457 deaths due to avian influenza had been reported to the World Health Organisation [WHO] from 21 countries,” says the UKHSA.
Importantly it adds: “The vast majority of human cases have reported contact with poultry and there is no reported evidence of sustained human-to-human transmission. No major changes have been detected in recently characterised viruses from human cases”.
That’s the encouraging part.
But what’s worrying is that the virus has now been found in mammals, together with genetic mutations which, in the cautious language of science, carry with them “public health implications”.
The foxes and otters found infected in the UK are, in themselves, probably nothing to worry about because they almost certainly became infected not by mixing with others, but by eating the carcasses of dead and infected birds. In other words, these infections almost certainly die with the animal concerned.
More worrying is what has been found and recently reported in a mink farm in Spain.
‘We are playing with fire’
The story there started early last autumn, when dead seagulls and gannets began to wash up on the coast of Galicia in the north-west of the country. Then in October, something unusual happened. At a fur farm a few miles inland, thousands of mink started to die from the same avian virus.
Scientists believe conditions at the farm, where tens of thousands of animals were kept in densely packed pens, had allowed the virus to mutate and spread between the mink.
Within weeks, more than 4 per cent of the mink had died from haemorrhagic pneumonia caused by the virus. Workers were given antiviral drugs and placed in quarantine and the remaining 50,000 animals were promptly culled. Thankfully, none of the farm workers was infected.
Experts say that what happened at the mink farm in the Galician city of A Coruña is exactly the kind of “spillover event” that could lead to the next human pandemic.
A paper published in Eurosurveillance two weeks ago said the virus found in the Spanish mink carried a mutation to the “PB2” gene – one similar to that found when avian flu jumped to pigs over a decade ago.
“Our findings also indicate that an onward transmission of the virus to other minks may have taken place in the affected farm,” wrote the authors. Ongoing fears are that such farms could act as incubators and, perhaps, reservoirs for the virus – just as they have done with Covid and other zoonotic diseases.
“It didn’t happen this time, and it may not happen, but this is one of the scenarios from which a new pandemic could originate,” said Marion Koopmans, head of the department of virology at the Erasmus Medical Centre in Rotterdam. “We are playing with fire.”
For now, most scientists think the chances of the virus mutating enough to spread efficiently in humans is unlikely. In the medium term, however, it’s a bit of a numbers game. There are hundreds of millions of birds around the world sick with the virus and there are hundreds of thousands of densely packed fur farms which could become infected and further mutate the bug – the vast majority of which are in China and south-east Asia.
‘This is something we don’t want to see’
Jeremy Farrar is director of the Wellcome Trust and was recently named as the next chief scientist at the WHO. He feels that the greatest risk of the next pandemic comes from intermediate animal species – creatures that could bridge the gap between birds and humans.
Responding to the report on the Spanish mink farm, he tweeted: “Personal view. Greatest risk [of] devastating flu pandemic is avian/animal flu that infects [an] intermediate mammal.”
According to Prof Koopmans, a member of the WHO team that was charged with tracing the origins of Covid, the global distribution of H5 bird flu viruses has changed significantly since 2020.
“Now it looks like it can spread between mammals, and this is something we don’t want to see. This means there is an opportunity for a virus from the risk list to pick up mutations which could make it transmissible between humans.”
The only human case of bird flu so far recorded in the UK was duck keeper Alan Gosling, who caught the virus last year at his home in Devon. The 79-year-old tested positive during routine swabbing after the flock of Muscovy ducks he kept at his home in Buckfastleigh, Devon, became infected.
Gosling, who survived, remains Britain’s only confirmed case to date, although all workers on infected UK poultry farms are being offered antivirals and are carefully tested.
In addition to antivirals, there are prototype human vaccines that have been developed to fight H5N1 viruses should they start to spread in humans. Some are stockpiled but in the event of a sustained human outbreak, new vaccines would have to be developed that are specific to the strain of the virus involved.
According to Matthew Baylis, the Oxendale chair of veterinary epidemiology at the University of Liverpool, the combined circumstances of a widespread bird flu outbreak and non-biosecure mink farms present a clear danger.
“We worry about influenza viruses that are a mix and affect different hosts, as we saw with H5N1 and swine flu [in 2009],” he said. “What we don’t want is this virus that is circulating massively [in birds] to get better at infecting people.
“In the end we might see one of these [mutations] that is really severe.”
The biggest risk is the continuing existence of fur farms. In 2021, 755 mink farms existed in the EU – down from a pre-pandemic figure of 2,900 – producing 27 million pelts a year.
Most of the remaining farms are in Finland, Poland, Lithuania and Greece. Spain is a tiny player with a little over 20 facilities, almost all in Galicia. China and south-east Asia present the biggest worry.
Animal rights organisations have long called for a ban on fur farming, chiefly on animal welfare grounds. Now public health experts are calling for change.
“I think the public health risk is so high, it outweighs any benefits of having such farms,” said Elisa Pérez, a virologist from Spain’s Animal Health Research Centre.
Dr Pérez, who is a specialist in zoonotic diseases, which jump from a non-human host to a person and vice versa, questioned the security of fur farms in Spain, noting that mink continue to escape on a regular basis.
She said: “Even if we make an installation biosecure, there is still the risk of transmission between the mink and human workers, so the authorities need to consider whether it is in the public interest to maintain these reservoirs of potential infection.”
Prof Koopmans said that screening of factory farms housing mink and other species such as pigs is a sensible step, offering the chance of early detection to deal with the next spillover virus.
However, she warned that the risk of a new and deadly virus emerging can never be ruled out. “Plenty of animals can move in and out of mink farms. Birds and bats fly in, cats and rats also. Even if people are very careful around these animals, nature can do the trick,” she said.
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