Mink-Coronavirus “Cluster-5”: Why Experts Want to Quickly Eradicate It
Explaining why coronavirus evolution in minks poses a threat, leading to the decision to cull 17 million minks in Denmark.
Denmark has decided to slaughter all farmed minks — 17 million of them — due to a mutated SARS-CoV-2 found circulating in over 200 mink farms. The mink-coronavirus first infected 12 workers and 200 more humans later, although the workers did not seem to show worse Covid-19. About 400 farms were already culled. Owing to the mink-coronavirus outbreak, the U.K. has just banned travelers from Denmark.
And the WHO is aware of the situation, naming the mink-coronavirus “cluster-5” variant with a set of mutations not previously seen. “Preliminary findings indicate that this particular mink-associated variant identified in both minks and the 12 human cases has moderately decreased sensitivity to neutralizing antibodies,” the WHO stated, but also mentioned that more data is needed.
Culling to eradicate mink-coronavirus
The Danish government reported that the mink-coronavirus has several mutations in the spike protein — the virus component that binds to the ACE2 receptor on human cells — making it more resistant to human antibodies than usual. As vaccines mainly target the spike protein, there’s a risk of future vaccines not working against mink-coronavirus if it becomes widespread in humans. And this might lead to another Covid-19 (or mink-Covid) pandemic.
So, “it is necessary to kill all mink,” said Mette Frederiksen, Denmark’s prime minister. “This is extremely serious, and a threat to the entire world,” she added. Kare Molbak, professor and director of State Serum Institute of infectious diseases, agreed, “The worst-case scenario is a new pandemic, starting all over again out of Denmark.”
“There is always a balance of risk. In this case … you need to act in time instead [of] waiting [to] get all the evidence. You need to act in time and stop transmission.”
The Denmark situation is not entirely new. A million minks — many with symptoms of Covid-19 — were previously gassed to death in Spain and the Netherlands. SARS-CoV-2 outbreak in farmed minks had also occurred in Sweden, Italy, and the U.S. That makes six countries in total.
To wait vs. to take action?
A few experts are hesitant, suggesting that the decision to mass slaughter minks may be too rushed. The full genome of the mink-coronavirus is not yet released. And scientists know nothing about how the mink-coronavirus behave in experimental settings or its biological properties.
“We need to wait and see what the implications are, but I don’t think we should come to any conclusions about whether this particular mutation is going to impact vaccine efficacy,” agreed Soumya Swaminathan, the WHO’s chief scientist. “We don’t have any evidence at the moment that it would.”
Francois Balloux, professor and director at the University College London Genetics Institute, believed that it’s ‘idiotic’ that vaccine-resistant SARS-CoV-2 would arise from minks. Instead, it might arise when vaccines administration becomes widespread as the selection pressure would be greater. For instance, antibiotic-resistant bacteria dominate as antibiotics usage increases.
“This variant can develop further, so that it becomes completely resistant, and then a vaccine does not matter. Therefore, we need to take [the mutation] out of the equation. So it’s serious.”
While the Danish government admitted that they have no foolproof evidence to back their decision, they rather err on the safe side. As Tyra Grove Krause, MD, Ph.D., infectious disease epidemiologist at the State Serum research institute, said, “There is always a balance of risk. In this case…you need to act in time instead [of] waiting [to] get all the evidence. You need to act in time and stop transmission.”
The reason for the mass culling of minks
First, let’s recall how the pandemic started. The closest known relative of SARS-CoV-2 is the bat coronavirus called RaTG13 that shares 96% genomic identity. And the 4% genomic differences reflect decades of evolution gap. This indicates that an intermediate host facilitating coronavirus evolution is involved, as was the case with SARS and MERS.
Regardless, the important concept is that evolution accelerates in a different host. A different host brings a distinct biological system that the coronavirus — or any viruses for that matter — has to adapt to. The pressure to survive is greater. And mutation rates will soar, which happened when MERS and SARS first adapt to humans. (But such rapid evolution did not happen with SARS-CoV-2 at the start of the pandemic, implying that SARS-CoV-2 might have been circulating in humans before December 2019; more details here.)
If the rapid evolution continues, a new coronavirus strain might emerge, and here lies an unknown future.
The accelerated evolution could explain the mutated spike protein of mink-coronavirus. SARS-CoV-2 probably had to adapt to the mink ACE2 receptor, thereby changing its spike protein and evolving into mink-coronavirus, theorized Ian Jones, a virologist professor at the University of Reading. If the rapid evolution continues, a new coronavirus strain might emerge, and here lies an unknown future.
“A large virus reservoir in mink increases the risk of new virus mutations occurring again, which vaccines may not provide optimal protection against,” the State Serum Institute in Denmark cautioned. “This variant can develop further so that it becomes completely resistant, and then a vaccine does not matter,” agreed Allan Randrup Thomsen, professor of virology at the University of Copenhagen. “Therefore, we need to take [the mutation] out of the equation. So it’s serious.”
While the present mink-coronavirus could infect humans, there is also a chance that it may lose the ability as it evolves. “Of course, the mink version may not transmit well to man, so it’s a theoretical risk,” Prof. Jones added. “But Denmark is clearly taking a precautionary stance in aiming to eradicate the mink version so that this possibility is avoided or made much less likely.”
In Denmark, a new mutated SARS-CoV-2 in minks had infected over 200 humans and was less susceptible to antibodies. The WHO called the mink-coronavirus the “cluster 5” variant. Denmark then decided to cull all 17 million minks, a decision a few experts questioned, especially when the mink-coronavirus genome is not yet released or studied for its biological functions. Yet Denmark decided to act first despite insufficient evidence to avoid the possibility that mink-coronavirus may lead to vaccine resistance and, worse, another pandemic. This rationale may be justified considering that coronavirus evolution and mutation accelerates in a different host.