At the beginning of last October, minks on a fur farm in Spain suddenly started falling ill. He stopped eating and started drooling profusely. They became clumsy, experienced tremors and developed bloody snouts.
At first, experts suspected that the coronavirus might be to blame. This was a reasonable assumption; Since the start of the COVID-19 pandemic, the virus has repeatedly found its way onto mink farms, sparking large animal outbreaks, triggering massive mink culls and temporarily halting mink farming.
But it was not the coronavirus that had infiltrated the Spanish mink farm, scientists soon discovered. It was H5N1, a highly pathogenic strain of avian influenza.
Over the past few years, a new strain of H5N1 has spread widely through wild and domestic bird populations around the world. It has taken an unusually heavy toll on wild birds and has repeatedly spread to mammals, such as foxes, raccoons and bears, that may feed on infected birds.
But the mink farm outbreak was a new and troubling development, the scientists said. In Spain, the virus appeared to be spreading from mink to mink. It also contained an unusual mutation that may be a sign of adaptation to mammals, the scientists reported recently in a paper in the journal Eurosurveillance.
Dr Thijs Kuiken, a veterinary specialist at the Erasmus University Medical Center in the Netherlands, said the outbreak “confirmed a fear I had” that the virus could spread efficiently among mammals.
There is no evidence that the mink, which were all killed, transmitted the virus to humans, and experts insisted the outbreak was not cause for panic. But it is a reminder of some of the risks posed by mink farms — places in which large numbers of susceptible animals are kept in facilities with porous boundaries to the outside world — and highlights the need for more active disease surveillance and other precautions. , the experts said.
“Should we be concerned about this? No,” says Dr. John, a veterinary pathologist at the College of Veterinary Medicine at Washington State University. Chrissy Ekstrand said. “But should we be on the alert and prepared? I think absolutely we should.
mink mortality
In Spain, the first signs of trouble came during the first week of October, when mortality rates increased on a mink farm in Caral. First, the deaths were confined to a subset of the farm’s barns, which collectively housed more than 50,000 minks. But in the weeks that followed, the outbreak spread across the farm.
“The mechanism of transmission inside the farm is still unknown, but it is clear that the virus was able to move,” said Dr Isabella Monne. A veterinarian at the European Union Reference Laboratory for Avian Influenza and Newcastle Disease, and author of the Eurosurveillance paper.
Laboratory testing revealed that the mink were infected with H5N1, and all the animals were subsequently culled.
Exactly how the virus got into the mink is unknown. Farmed mink, including Spanish farms, are often fed raw poultry, which presents a potential risk.
“If they are fed poultry and poultry byproducts infected with an avian influenza strain, those minks can get avian influenza,” Dr. Casey Barton Behravesh, who directs the One Health Office at the Centers for Disease Control and Prevention.
But in this case, there was no evidence that poultry farms that supplied feed to mink farms had experienced outbreaks of avian influenza, and scientists said the most likely source of the virus was a wild bird.
In the weeks prior to the mink farm outbreak, the virus had been detected in wild birds in the area. And the minks on the Spanish farm were kept in barns that didn’t completely close over the sides. This is a common feature of mink barns, which are usually left partially open to improve air flow, said Dr. Kuiken, who has studied the coronavirus between wild animals and farmed minks on Dutch mink farms. The possibility of transmission has been studied.
“It was really disturbing for us to see how open they were to the environment,” Dr Kuiken said, “and how easy it was for both mammals and wild birds to visit these mink farms and interact with the mink Was.”
Experts said wild birds and other animals may be particularly attracted to mink food, a meaty pulp or paste that is usually spread on top of the animals’ wire cages.
“It’s like a free buffet for these animals to come and eat,” said Dr. Barton Behravesh.
(Dr. Monne stressed that wild birds were also “victims” of the virus, however, and should not be blamed or targeted.)
animal restraint
Minks are usually kept in high densities, with their cages close together. This habitat arrangement, combined with a lack of genetic diversity among farmed minks, could make it easier for a virus to find its way into minks, the scientists said.
And once a virus begins to spread, it begins to pick up new mutations and adapt to its new hosts. Indeed, the researchers found that the flu virus isolated from mink in Spain had several mutations that distinguished it from sequences isolated from birds. One of these mutations, in particular, has previously been shown to help influenza better replicate in mammalian cells.
Still, the significance of some of the mutations is unknown, and researchers cannot rule out the possibility that they were present in the virus before finding their way into form, the scientists cautioned.
Globally, the H5N1 variant that is circulating in birds has caused fewer than 10 known cases in people since December 2021, and there are no documented instances of human-to-human transmission, according to the CDC.
“The H5 virus is not well adapted to humans,” said veterinarian Dr. Jim Lowe of the College of Veterinary Medicine at the University of Illinois at Urbana-Champaign.
The fact that the virus showed up on a mink farm is not particularly surprising, he said, and is not necessarily a cause for alarm. “It is not, to my mind, a particularly worrying situation for human health,” Dr Lowe said. “Obviously it’s not great for the mink.”
But a mink-adapted version of the virus may present a greater potential risk to people. “It is more likely that such viruses would spread efficiently between humans more easily,” Dr. Kuiken said.
Eleven farm workers had contact with minks; Dr. Monne and his colleagues reported that all tested negative for the virus. The fact is “reassuring,” said Dr. Monne. “But clearly, the worrying thing is that this virus is spreading everywhere.” This means mink and other mammals will have more opportunities to become infected and potentially spread the virus.
The permeability of mink farms also means that a virus spreading in mink can make its way through the farm. Scientists have found that mink sometimes escape from farms, and that dogs and cats on mink farms with coronavirus outbreaks have also been infected with the virus.
These animals could potentially act as intermediate hosts, passing the mutated mink version of the virus onto humans or wild animals. In a recent study, Dr. Barton Behravesh and colleagues used GPS collars to track the movements of free-roaming cats living on or near several Utah mink farms experiencing coronavirus outbreaks. Did. The researchers found that the cats roamed widely.
“They made frequent visits to the mink shed, freely moved around the affected farms, visited surrounding residential properties and neighbourhoods,” Dr Barton Behrwesch said.
To date, highly pathogenic avian influenza has not been detected on any mink farm in the United States, said Lindsay Cole, spokeswoman for the Animal and Plant Health Inspection Service. US Department of Agriculture.
But with the virus being so widespread, more active influenza surveillance — including regularly sampling animals for asymptomatic infections — is needed on mink farms, the scientists said.
Dr. Barton Behrwesch said, the mink “is definitely an animal that warrants an increase.”
Experts said that ensuring mink have clean food and water sources and that farm workers follow basic sanitation and hygiene practices can help reduce the risk on mink farms.
But Dr. Kuiken said more sweeping changes may be needed. “You also have to think first whether you want a mink farm,” he said. “We need to think more about our human activities in a way that tries to prevent the problems we’re seeing, for example, with the emergence of infectious diseases, to mitigate them or to prevent them after they occur.” Instead of trying to solve” we have appeared.”