A mutant form of coronavirus found in Denmark mink farms have made an appearance previously, scientists say.
The mutant virus which appears to have spread from animals to humans in Denmark, has been detected retrospectively at a mink farm in the Netherlands, according to a leading Dutch expert.
The mink were culled and the mutation did not infect humans there, he said.
Six countries have reported coronavirus outbreaks at mink farms. They include the Netherlands, Denmark, Spain, Sweden, Italy and the US.
Mink are known to be susceptible to Sars-CoV-2, the virus that causes Covid-19, which can spread rapidly from animal to animal in conditions where thousands of animals are kept in close proximity.
The farmed weasel-like animals have become infected by farm workers during the pandemic, and have occasionally passed the virus on to humans, raising the risk of the virus acquiring mutations.
Danish scientists are worried that genetic changes in a mink-related form of the virus, infecting a dozen people, has the potential to make future vaccines less effective.
The genetic change is in the spike protein of the virus, which is important in the body’s immune response, and a key target for vaccines.
The Danish genome sequences released recently on a public database, allowing scientists in other countries to look for evidence of the mutation.
Prof Wim van der Poel, a veterinary expert at Wageningen University, said analysis of genetic data from the Netherlands revealed one previous case of the mutation at a mink farm there in early May.
The Netherlands launched a widespread cull of mink after signs, in a small number of cases, that humans had picked up coronavirus from mink.
A number of animals have caught the virus from humans, but mink appear particularly susceptible.
Prof Dirk Pfeiffer, of the Royal Veterinary College in London, said while mutations in viruses happen all the time as they spread, the question is whether these change the characteristics of the virus.
“At this stage, it seems to be that there may be issues with vaccine effectiveness, but this is still unclear,” he said.
Effective surveillance is needed to detect emergence of new pathogens early, and then have an effective way of responding, he added.
In Sweden, there have been outbreaks at mink farms in the south-east part of the country. Scientists reported that the genetic mutation found in Danish mink had not been detected so far.