COVID-19: Why Is the Virus Transmitted Through Mink More Dangerous?

Denmark, the world’s leading mink farm producer, is preparing to cull all 17 million animals raised within its borders. The reason is a new COVID-19 variant that is believed to have emerged in mink and threatens the effectiveness of a future vaccine for humans. But why is the virus’s transmission through an animal reservoir so dangerous? It is no longer pangolins but mink that are in the crosshairs, after six countries—namely Denmark, the Netherlands, Spain, Sweden, Italy, and the United States, reported cases of SARS-CoV-2 in mink farms. But the real problem isn’t so much that the animals become infected by humans, but rather that they can reinfect humans. In fact, these are the first reported cases of transmission from animals to humans. As such, minks become a reservoir population for the virus, where it can proliferate and mutate with even less control than in humans. The animals are raised in confined spaces, which means the virus spreads rapidly there. This rapid replication in animals—which is less controlled than in humans—makes them an ideal breeding ground for new mutations that can then be transmitted to humans. This is what happened recently in Denmark and is likely to happen again if the infection is not brought under control in mink populations. To date, seven different mutations of the SARS-CoV-2 spike protein have been identified in mink, four of which are specific to a single SARS-CoV-2 variant. And these mutations differ from those generated by human-to-human transmission and replication. However, not all viral mutations are cause for concern. It is normal for a virus to mutate, and this does not necessarily mean the virus will behave differently. What is alarming authorities and prompting them to take such drastic measures is that one of the identified mutations is associated with reduced effectiveness of human antibodies . This does not translate into more severe effects in humans, but the virus mutated via minks could create the risk that a future vaccine will not work as it should, Prime Minister Mette Frederiksen stated during a press conference with Danish health officials. The mutated virus “does not respond as much to antibodies as the normal virus. The antibodies still have an effect, but they are not as effective ,” said Kåre Mølbak, head of the Danish Infectious Disease Control Authority (SSI). According to Health Minister Magnus Heunicke, “Research has shown that mutations could affect current COVID-19 vaccine candidates.  “This poses a threat to the development of coronavirus vaccines, which is why we must launch a national campaign ,” he emphasized. What frustrates scientists tracking the virus’s evolution, however, is the lack of transparency regarding the data. The DNA sequences of the SARS-CoV-2 variant in question have not yet been published, so it is impossible at this stage for researchers to comment on the policy decision. Determining the concrete consequences of a mutation is inherently complex. Since the changes in the spike protein have not yet been evaluated by the international scientific community, the implications are not yet clear, said James Wood, head of the Department of Veterinary Medicine at the University of Cambridge. “It is too early to say whether the changes will lead to vaccine failure or a loss of immunity ,” he said. At present, there is no evidence that animals, including mink, play a significant role in spreading the virus to humans, according to the authorities in charge. It is more likely that viral transmission among human populations is of human origin. “Culling mink cannot in itself eliminate the strain, but it can prevent other mutant strains from developing in mink,” according to Wood. And unfortunately, Danish health authorities are unwilling to take that risk. They explain that there are currently no signs that the infection on mink farms is declining over time. In the absence of vaccines, viable treatments, or ways to enforce social distancing among the animals, the only effective—albeit radical—solution known to date is to cull the animals before the risk becomes too great. Culling animals is a common practice to limit the spread of epidemics among animals. In Europe, we remember all too well the millions of animals killed to limit the spread of mad cow disease, for example. More recently, millions of pigs were culled in Asia to combat African swine fever. Mink are merely the latest victims of the lack of effective means to combat certain diseases. Humans would not be the only ones to benefit from a vaccine or effective treatment against COVID-19.