Can wild animals shape people?
Sars-CoV-2: Animals could serve as a retreat for the virus
No laboratory or field study could have prepared science for what happened on the mink farms, says Linfa Wang of Duke National University in Singapore. “The virus taught us a lesson. It said: 'You cannot stop me'. "
The virus taught us a lesson. It said, 'You can't stop me'. (Linfa Wang, Duke-National University, Singapore)
An unusual cluster of mink deaths on two Dutch farms, combined with a powerful surveillance system, drew the researchers' attention to the first outbreaks in April. By the end of 2020, Sars-CoV-2 had reached 70 farms in the Netherlands, as well as farms in about a dozen other countries including Denmark, Greece, Canada and the United States.
Sawatzki describes the situation on the farms as "the perfect storm". The animals, which are susceptible to infection, are crammed together and have regular direct contact with infected farmers. On a Danish farm, around 97 percent of the mink tested had antibodies against Sars-CoV-2. Eight days earlier it was only 6 percent, says Anette Boklund, epidemiologist at the University of Copenhagen.
As the virus multiplies in infected animals, it can change slightly. This leaves traces in its genome that suggest previous hosts. By sequencing the virus genomes and trying to understand the interactions between infected humans and animals, researchers in the Netherlands confirmed in mid-2020 that two farm workers at mink had contracted Covid-19 from these animals. That was the first evidence that animals can pass the virus on to humans. So far, at least 60 people are suspected of having caught the virus in minks, says Wim van der Poel, virologist at Wageningen University & Research in Lelystad in the Netherlands.
Some researchers fear that, over time, tiny mutations in the genome of hundreds or thousands, if not millions, of mink could add up to changes that make the virus more contagious or deadly to humans. It may then be able to defy drugs or vaccines. In November 2020, researchers in Denmark isolated several virus variants from mink. One of them could not harm the antibodies of people who had already gone through Covid-19. However, this variant was only detected in a total of twelve people and not since mid-September, which indicates that none of these people passed it on.
A few weeks later, on October 1, 2020, researchers from the U.S. Department of Agriculture captured the wild, corona-positive mink from Utah.
Marion Koopmans is studying virology at the Erasmus University Medical Center in Rotterdam, the Netherlands. She says it didn't surprise her that a wild mink caught the virus. Litter and dust from the affected farms had been shown to be heavily contaminated. Sometimes minks escape from farms and settle in the wild. More than a dozen mink have already tested positive for Sars-CoV-2 RNA or antibodies in the USA and the Netherlands. While the animals were caught in the wild, they were all likely farm breakouts with active outbreaks.
Some countries have taken far-reaching measures to prevent the virus from spreading in minks. Denmark, the world's largest producer of mink fur, and the Netherlands have culled all of their mink populations. This involved a total of almost 20 million animals. Other countries are considering vaccinating their mink. The pandemic is accelerating the end of mink breeding, says Drexler.
The story with the mink and Covid-19 has confirmed the researchers' early fears. The virus can find refuge in animals in ways that are difficult to predict and hardly controllable, and then leap back to humans. Whether Sars-CoV-2 can efficiently spread among wild animal populations is still unknown, says Koopmans, who monitors wild minks in the Netherlands. “Minks tend to be loners on their own. That could be an advantage for us, ”she says.
Scientists are also wondering what is happening in China to minks and other animals bred for fur, such as the raccoon dog. Some researchers believe that the fox-like animal may have been an intermediate host for the first Sars virus. Overall, very little has so far been published on Sars-CoV-2 and animals from China, although a team from the World Health Organization (WHO) is investigating the origins of the coronavirus there. At a press conference on February 9, 2021, it said the results of tests on wild and bred animals across China had shown no evidence that the virus was circulating in these animals.
Virus researchers are on alarm around the world
Efforts to monitor infections in animals are becoming more consistent around the world. Both the OIE, the WHO and the US Centers for Disease Control and Prevention have each issued a guide. None of them recommend large-scale testing, but the WHO advocates testing animals in the vicinity of infected fur farms. The OIE meets monthly with on-site researchers to discuss the latest findings on animals in the pandemic.
At these meetings, the new variants that are circulating in humans are now also being discussed. Any change in the virus can also affect how it affects animals, says Gryseels.
Research teams have not yet studied how well the variants, which were first discovered in the UK, South Africa and Brazil and which spread faster, can infect animals. However, all new variants contain a mutation that the virus makes for laboratory mice (Mus musculus) infectious. The animals are resistant to the "normal" virus. The worldwide distribution of the new variants increases the possibility that house mice, and perhaps rats as well, infect humans through contaminated environments such as sewers, says Gryseels.
Some researchers sequence viruses isolated from infected animals and monitor them for important mutations. "We are in a risky position worldwide," says Daszak. "There will be other surprises besides the mink."
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