When the Danish government learned that a mutated strain of coronavirus was spreading through the country’s farmed mink population, it initially planned to cull 15 million of the creatures. But while the scheme is now mired in legal and political controversy, it has raised wider questions about animals’ ability to pass mutated versions of the virus back to humans, potentially undermining any vaccine, and how conditions in intensive farming could be fuelling this risk.
Coronavirus, like all viruses, can mutate as it replicates. Hundreds of thousands of people are infected with Sars-CoV-19 daily, and there are documented cases of it passing to animals, including pets such as cats and dogs. The more often the virus replicates, the higher the likelihood of a mutation.
Most of these minute changes have no effect on the disease itself, particularly because they do not involve the virus jumping from one species to another. But if a virus does cross the species barrier, that newly infected species can become a reservoir of the virus, said the University of Bath’s Samuel Sheppard, who has studied zoonoses (pathogens that begin in animals before spreading to humans).
In crowded conditions, such as on a mink farm, a disease like coronavirus can spread rapidly, mutating as it replicates. The mutated virus may then jump back to humans, potentially rendering existing treatments ineffective. Mink are especially worrying as they seem to be one of the few animals that can transmit coronavirus back to humans. “When you have a large population of viruses that comes from having a large population of animals, such as farmed mink – that is when more mutations arise,” Sheppard said.
The Statens Serum Institut (SSI), a Copenhagen-based research institute studying infectious diseases, says that one mutation of coronavirus linked to mink farms, named Cluster 5, is of particular concern. The SSI’s recommendations led to the decision to cull the country’s mink population after 12 cases of coronavirus in humans were determined to emanate from the Cluster 5 strain. However, the cull order was criticised by opposition politicians who cast doubt on its scientific basis and questioned whether a full cull was a proportionate response to the risk posed. It has since been suspended pending legal approval.
Concern revolves around the virus’s spike protein, which the coronavirus uses to penetrate a cell. After humans are infected with coronavirus, they develop antibodies to the spike protein, which most Covid-19 vaccine candidates depend on replicating. The Pfizer vaccine, which has been shown to be 90 per cent effective in preliminary results of phase three trials, uses mRNA technology to produce the spike protein, which in turn teaches the body to produce antibodies.
The SSI fears that antibodies against the non-mutated virus would be less effective against the Cluster 5 variation, opening up the possibility of reinfection and existing vaccines being ineffective against the new strain. In the worst-case scenario, some scientists are concerned that, left unchecked, the Danish variation could kickstart a new pandemic entirely.
The SSI warned that maintaining operating mink farms increased the likelihood of further mutations. “The SSI believes that continued mink breeding would entail a significant risk of recurrence of a large spread of infection among mink and humans,” the institute wrote in a statement.
[See also: How Covid-19 exposed the meat industry’s abuses]
Millions of mink have already been culled this year in countries including the Netherlands and Spain. Regardless of the individual approach taken by different nations, the Cluster 5 mutation has brought into ever greater focus the effect intensive animal farming can have on epidemics.
Economic pressures, which encourage farmers to pack many animals in as small a space as possible, are often at odds with good practice preventing the mergence of pathogens, Sheppard said. “With more responsible farming practices, the probability of these sorts of events occurring would be greatly reduced.”
A more responsible attitude to animal farming would likely not only help safeguard the success of new Covid-19 vaccines, but also reduce the likelihood of the next pandemic emerging at all.