Avian flu is, at this point, somewhat of a misnomer. The virus, which primarily affects birds, is spreading uncontrollably across much of the world, devastating not only birds, but large swaths of the animal kingdom. Foxes, cats and pigs have fallen ill. Bears have become blind. Marine creatures, including seals and sea lions, died in great numbers.
But none of the sick animals caused such anxiety as the mink. In October, an outbreak of avian influenza occurred on a Spanish mink farm, killing thousands of animals before culling the rest. It later became clear that the virus had spread among animals, picking up a mutation that helped it thrive in mammals. This is likely the first time that a mammal-to-mammalian spread has led to a major outbreak of avian influenza. Since mink is known to spread certain viruses to humans, there was a fear that disease could be transmitted from mink to humans. No humans became ill from the outbreak in Spain, but other mink infections have spread to humans before: In 2020, a COVID outbreak in Danish mink farms led to new mink-associated variants spreading to a small number of humans.
As mammals, we have good reason to be concerned. An outbreak of disease in crowded mink farms is the perfect scenario for avian influenza to mutate. If, in doing so, he captures the potential to spread among humans, another global pandemic could potentially start. “There are many reasons to worry about mink,” Tom Peacock, an influenza researcher at Imperial College London, told me. At the moment, mink is a problem that we cannot ignore.
For an animal with two very different body types, mink and humans have some unusual similarities. Research indicates that we share similar receptors for COVID, bird flu, and human flu, through which these viruses can enter our bodies. The numerous outbreaks of COVID on mink farms during the early pandemic, and the outbreak of avian influenza in Spain, seriously illustrate this point. James Lowe, a professor of veterinary medicine at the University of Illinois at Urbana-Champaign, told me that it’s “not surprising” that mink can contract these respiratory illnesses. Mink is closely related to rodents, which are well known to be susceptible to human influenza, making them the preferred model for influenza research.
Minks wouldn’t get sick as much, and it wouldn’t be much of a problem for humans, if we didn’t continue to farm them for fur in the ideal conditions for an outbreak. Many pens used for mink breeding are partially outdoors, allowing injured wild birds to come into contact with the animals, not just air but potential food as well. Mink farms are also notoriously tight: a Spanish farm, for example, kept tens of thousands of mink in about 30 pens. Transmission of the virus would be assured in these conditions, but animals are particularly vulnerable. Minks are typically solitary creatures, Angela Bosco-Luth, professor of biomedical sciences at Colorado State University, told me that they face great stress in crowded pens, which can make them more susceptible to disease. And since they often breed so that their coats look alike, the entire population may share a similar genetic susceptibility to disease. The frequency of outbreaks among mink, Bosco-Lauth said, “may actually have less to do with the animals and more to do with the fact that we’re raising them the same way…we’re going to have intensive cattle or chicken farming.”
So far, there is no evidence that mink from the Spanish farm spread avian influenza to humans: none of the workers tested positive for the virus, and since then, no other mink farm has reported an outbreak. “We’re not very susceptible to bird flu,” Lowe said. Our bird flu receptors are embedded deep in our lungs, but when we’re exposed, most of the virus is picked up in our nose, throat, and other parts of our upper respiratory tract. This is why avian influenza infection is less common in people but is often at the level of pneumonia when it does occur. In fact, very few humans got sick and died from bird flu in the 27 years that the current strain of bird flu, known as H5N1, has been around. This month, a girl in Cambodia died from the virus after encountering a sick bird. The more the virus spreads in the environment, the higher the chances of a person becoming infected. “It’s a potion thing,” Lowe said.
But our susceptibility to bird flu can change. Another outbreak of mink plants may give the virus more opportunities to continue mutating. The concern is that this could create a new variant that is better at binding to human influenza receptors in our upper respiratory tract, Stephanie Seifert, a professor at Washington State University who studies zoonotic pathogens, told me. Peacock, of Imperial College London, said that if the virus gained the ability to infect the nose and throat, it would be better for its spread. These mutations “would worry us more.” Fortunately, the mutts raised in the Spanish mink farm “were not as bad as many of us feel,” he added, “but that doesn’t mean that the next time this happens, that will be the case, too.”
Because minks carry receptors for both avian and human influenza, the researchers wrote in 2021, they can act as “mixing vessels” for viruses. Influenza viruses can switch parts of their genome, resulting in a type of Frankenstein disease pathogen. Although viruses remixed in this way are not necessarily more dangerous, they may be, and this is not a risk worth taking. “The three previous influenza epidemics arose due to mixing between avian and human influenza viruses,” said the peacock.
While there are good reasons to be concerned about mink, it’s hard to gauge how worried we should be — especially given what we still don’t know about this variant virus. After the death of the little girl in Cambodia, the World Health Organization calls the global bird flu situation “alarming,” while the CDC maintains that the risk to the public is low. “It’s definitely not a huge risk” for bird flu to pass on to humans, Lowe said, but it’s worth keeping an eye on. He added that H5N1 bird flu is not new, and has not affected people en masse yet. But the virus has already changed in ways that make it better at infecting wild birds, and as it spreads into the wild, it may continue to change to better infect mammals, including humans. “We don’t understand enough to make robust predictions of public health risk,” Jonathan Ranstadler, a professor of infectious diseases at Tufts University, told me.
As bird flu continues to circulate among birds and in populations of domestic and wild animals, it will become more difficult to control. The virus, which is officially seasonal, is already present year-round in parts of Europe and Asia, and is poised to do the same in the Americas. Breaking the chain of transmission is vital to preventing another pandemic. An important step is to avoid situations where humans, mink, or any other animal could be infected with human and avian influenza at the same time.
Since the outbreak of COVID, mink farms in general have stepped up their biosecurity: Farm workers are often required to wear masks and protective equipment, such as disposable clothing. To reduce the risk of mink — and other susceptible hosts — farms need to reduce their size and density, reduce contact between mink and wild birds, and monitor the virus, Ranstadler said. Some countries, including Mexico and Ecuador, have recently adopted avian influenza vaccines for poultry in light of the outbreak. H5N1 vaccines are also available for humans, although not as readily available. However, one of the most obvious options is to close mink farms. “Maybe we should have done that after SARS-CoV-2,” said Bosco Louth of Colorado State. However, doing so is controversial, because the global mink industry is valuable, and has a huge market in China. Denmark, which produces up to 40 percent of the world’s mink skins, temporarily banned mink breeding in 2020 after the wave of the coronavirus outbreak, but the ban ended last month, and farms have returned, albeit in a limited capacity.
Mink is not the only animal that poses a risk of avian influenza to humans. “Honestly, with what we’re seeing with other wildlife species, there really aren’t any mammals that I can rule out at this point in time,” Bosco-Lauth said. Any type of mammal that frequently catches the virus is a potential risk, including marine mammals, such as seals. But Ranstadler said we should be more concerned about people who come into contact with them a lot, especially animals raised at high density, such as pigs. Not only is this a public health concern for humans, he said, but the potential for “environmental disruption”. Avian influenza can be a devastating disease for wildlife, killing animals quickly and ruthlessly.
Whether or not avian influenza passes to humans, it won’t be the last virus to threaten us – or mink. The era we live in has come to be known as a “pandemic,” as my colleague Ed Young called it, an era defined by the regular spread of viruses in humans, due to our disruption of the natural pathways of viral movement in nature. Minks may not transmit avian influenza to us. But that doesn’t mean they won’t be at risk the next time a new influenza virus or coronavirus appears. Doing nothing about mink is basically choosing luck as a public health strategy. Sooner or later, it will run out.
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