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].
“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,” he said.
Most human cases of avian H5N1 occur in people working closely with birds. This was the case with duck keeper Alan Gosling, who caught the virus last year at his home in Devon.
He remains the UK’s only confirmed case to date, although all workers on infected UK poultry farms are being offered antivirals and are carefully tested.
However, the transmission of the virus among mammals in the UK will certainly ring alarm bells. On Thursday, the Animal and Plant Health Agency (APHA) said nine otters and foxes had recently tested positive for H5N1.
It is believed they had fed on dead or sick wild birds infected with the virus.
The animals were found to have a mutation of the virus that could make it easier to infect mammals, but there was no evidence of transmission between mammals. Nonetheless, such developments point to the rising dangers posed by H5N1.
Fur coats ‘not worth the risk’
At the affected mink farm in Galicia, employees wore face masks as a result of new protocols introduced in response to the Covid-19 pandemic and all came through the recent avian flu outbreak without infection.
Nevertheless, the propensity of mink to incubate and spread respiratory viruses that could transmit to humans is making scientists ask whether such farms should exist at all.
“Mink are mammals that are very good at harbouring flu virus and they are kept at close quarters so it can spread easily between them,” noted Prof Bayliss, adding that the farm in Galicia was not biosecure, with the cages kept in barns that were open at the sides.
“Wild birds could access the installation, and clearly there was an acquired mutation that allowed the virus to pass better from mammal to mammal. For the sake of fur coats this is a risk we don’t want to take.”
As of January 2021, Covid-19 had been detected in 400 mink farms across eight European Union countries.
A mutation found in the Sars-CoV-2 spike protein in some mink, even raised the possibility that the animals drive the emergence of new vaccine-resistant Covid strains.
“Mink are closely related to ferrets, which are used as a model for responses to human respiratory diseases – that really tells you everything you want to know,” said Prof Baylis.
After the detection of Covid in hundreds of its mink farms, Denmark ordered a cull of the entire population, as did the Netherlands, which closed the industry down for good.
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 just over 20 facilities, almost all in Galicia.