In early October last year, a mink on a fur farm in Spain suddenly started getting sick. They stopped eating and started salivating excessively. They became clumsy, began to experience tremors, and developed bloody noses.
Initially, experts suspected the coronavirus was the cause. It was a reasonable assumption. Since the beginning of the Covid-19 pandemic, the virus has repeatedly invaded mink farms, causing large animal outbreaks and causing the disposal of large numbers of mink, prompting a temporary moratorium on mink farming.
But scientists quickly discovered that it wasn’t coronavirus that invaded the Spanish mink farms. It was H5N1, a highly pathogenic strain of bird flu.
In recent years, new subspecies of H5N1 have spread widely in wild and poultry populations worldwide. It is disproportionately damaging to wild birds and has repeatedly affected mammals such as foxes, raccoons and bears that may prey on infected birds.
But the mink farm outbreak was a new and troubling development, scientists say. In Spain, the virus appears to have spread from mink to mink.It also contained an unusual mutation that could be a sign of adaptation to mammals, scientists report. in a recent paper In the journal Eurosurveillance.
Dr Thijs Kuiken, a veterinary pathologist at Erasmus University Medical Center in the Netherlands, said it “confirmed the fears I had” that the virus could spread efficiently between mammals.
There is no evidence that all-culled minks transmitted the virus to humans, and experts stressed that the outbreak was not the cause of the panic. However, this is a reminder of some of the risks mink farms pose, where large numbers of susceptible animals are housed in facilities with open boundaries to the outside world, and where more aggressive disease can occur. Experts said it underscores the need for surveillance and other precautions. .
“Should I be alarmed about this? No,” says Dr. Chrissy Eckstrand, a veterinary pathologist at the Washington State University College of Veterinary Medicine. “But should we stay vigilant and prepared? I definitely think we should.”
mink mortality
In Spain, the first signs of trouble appeared in the first week of October, when mortality soared on mink farms in Caral. Initially, carcasses were confined to a subset of the farm’s barns, which housed over 50,000 minks. But in the weeks that followed, the outbreak spread across the farm.
“While we don’t yet know the mechanism of transmission within the farm, it is clear that the virus was able to travel. He is a Veterinarian at the European Union Reference Institute for Avian Influenza and Newcastle Disease and author of the Eurosurveillance paper.
Laboratory tests revealed that the minks were infected with H5N1, after which all animals were culled.
It is not known exactly how the virus entered the mink. Farmed mink, including those from Spanish farms, are often fed raw poultry, a potential risk.
“These minks can potentially become infected with avian influenza if they are fed poultry or poultry byproducts infected with an avian influenza strain,” said Casey, director of the Centers for Disease Control and Prevention’s One Health Office. Dr. Barton Behravesh said.
However, in this case, there was no evidence that avian influenza occurred on the poultry farms that fed the mink farms, and scientists said wild birds were the most likely source of the virus.
The virus was detected in wild birds in the area weeks before the mink farm outbreak. Also, Spanish farm minks were housed in barns that were not fully enclosed on the sides. This is a common feature of mink barns, which are commonly left partially open to improve airflow, said Dr Kuiken, who studies possible coronavirus transmission. rice field. Between Wildlife and Farmed Mink On a Dutch mink farm.
“It was very disturbing for us to see how open they were to the environment,” said Dr Kuiken.
Wild birds and other animals may be particularly attracted to mink food, a meat-like mash or paste that is usually applied to the top of the animal’s wire cage, experts say.
“It’s like a free buffet for these animals to come and eat,” said Dr. Burton Belavesh.
(However, Monne emphasized that wild birds are also “victims” of the virus and should not be blamed or targeted.)
biological containment
Minks are usually densely housed in tightly packed cages. This housing arrangement, combined with the lack of genetic diversity in farmed mink, may facilitate the rapid spread of viruses that enter the mink throughout the farm, scientists say.
And as the virus begins to spread, it acquires new mutations and begins to adapt to new hosts. In fact, the researchers found that influenza viruses isolated from Spanish mink had multiple mutations that differed from the sequences isolated from birds. Notably, one of these mutations has previously been shown to help improve influenza replication in mammalian cells.
Still, the significance of some mutations remains unknown, and researchers caution that they cannot rule out the possibility that they were present in the virus before it invaded farms.
Globally, the H5N1 variant circulating in birds has fewer than 10 known human cases since December 2021. No documented instances According to the CDC, human-to-human transmission
“The H5 virus is not well adapted to humans,” said Dr. Jim Lowe, a veterinarian at the University of Illinois at Urbana-Champaign’s School of Veterinary Medicine.
The fact that the virus has appeared on mink farms is not particularly surprising and not necessarily alarming. “Obviously not very good for minks.”
But a mink-adapted version of the virus could pose a greater potential risk to people. Dr. Kuiken said.
Eleven farm workers had contact with mink. All had tested negative for the virus, Dr. Monne and her colleagues reported. That fact is “reassuring,” she said, Dr. Monne. “But what’s obviously worrisome is that this virus is spreading everywhere.” That means the virus has more chances to infect and spread to mink and other mammals.
The permeability of mink farms also means that viruses that begin to spread in mink can escape outside the farm. Mink farm dogs and cats With the coronavirus outbreak, scientists discovered that we are also infected with viruses.
These animals could potentially act as intermediate hosts and pass mutated mink versions of the virus to humans and wildlife.of a recent studyDr. Barton Behravesh and her colleagues used GPS collars to track the movements of free-roaming cats living on or around several Utah mink farms that have experienced coronavirus outbreaks. the researchers found.
“They frequented the mink hut, roamed freely around the affected farms, and visited the surrounding residential areas and neighborhoods many times,” said Dr Burton Veravesh.
Highly pathogenic avian influenza has not been detected on U.S. mink farms to date, said Lindsey Cole, a spokeswoman for the Animal and Plant Health Inspection Service. US Department of Agriculture.
But because the virus is so prevalent, mink farms need more aggressive flu surveillance, including regular sampling of animals with asymptomatic infections, scientists say.
Mink “is definitely a remarkable animal,” said Dr. Burton Belavesh.
Ensuring minks have clean food and water sources and farm workers adhering to basic hygiene and hygiene practices also help reduce risks on mink farms, experts say.
But Kuiken said more drastic changes may be needed. “You also have to consider whether you want to have a mink farm in the first place,” he said. “We need to think more about human activity in ways that try to prevent the problems we see, for example, the emergence of infectious diseases, rather than try to mitigate or solve them.” bottom. ”
