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This week’s decision by the Danish government to kill millions of minks due to coronavirus concerns, effectively wiping out a major domestic industry, has highlighted latent concerns among scientists and conservationists about the vulnerability of animals to the pandemic virus and what infections. among animals it could mean for humans.
The most worrying possibility is that the virus could mutate in animals and become more transmissible or more dangerous to humans. In Denmark, the virus has passed from humans to minks and back to humans, mutating in the process. Minks are the only animals known to have transmitted the coronavirus to humans, except for the initial spillover event from an unknown species. Other animals, such as cats and dogs, have been infected by exposure to humans, but there are no known cases of people being infected by exposure to their pets.
Versions of the virus that have mutated in the mink and spread to humans are no longer communicable or cause more serious disease in humans. But one of the variants, found so far in 12 people, responded less to antibodies in laboratory tests. Danish health authorities were concerned that the efficacy of vaccines under development could be diminished for this variant and decided to take all possible measures to stop its spread. This included killing every mink in the country and effectively blocking the northern part of the country, where the mutated virus was found. The UK has banned travelers from Denmark who are not UK citizens.
The World Health Organization and scientists outside of Denmark have said they have not yet seen evidence that this variant has any effect on vaccines. However, they have not criticized Denmark’s decision to cull its mink population.
Minks are not the only animals that can be infected with the coronavirus. Genetically modified dogs, cats, tigers, hamsters, monkeys, ferrets, and mice have also been infected.
Dogs and cats, including tigers, appear to suffer few ill effects. The other animals, used in laboratory experiments, have shown variable responses. However, farmed minks have died in large numbers in Europe and the United States, perhaps in part due to the crowded conditions on those ranches, which could increase the amount of exposure.
However, public health experts are concerned that any species capable of infecting it could become a reservoir that allows the virus to reappear at any time and infect people. The virus is likely to mutate in other animal species, as it has been shown to mutate in mink. Although most mutations are likely harmless, SARS-CoV-2 could possibly recombine with another coronavirus and become more dangerous. Conservation experts also worry about the effect on animal species that are already in trouble.
One approach to studying susceptibility has been to look at the genomes of animals and see which ones have a genetic sequence that encodes a protein in cells called the ACE2 receptor, which allows the virus to attach itself. A team of researchers studied the genomes of more than 400 animals. Another group did a similar study of primates, which are often infected with human respiratory viruses.
“One of the premises for doing this research was that we thought great apes would be at risk because of their close relationship with humans, genetically,” said Amanda D. Melin, an anthropologist at the University of Calgary and author of the primate study.
But, she added, she and her colleagues also wanted to consider “all other primates and their potential risk.” In addition to investigating genomes, the team also performed a computer model of the interaction of the virus’s spike protein with different ACE2 receptors.
The findings of both articles were mutually reinforcing, revealing that old world monkeys and all apes are most at risk. Both articles were published as non-peer-reviewed studies earlier this year.
Dr. Melin and her colleagues have been speaking with representatives of wildlife sanctuaries and zoos about the need for caution. Many of these facilities have greater restrictions on interactions between people and primates.
Zarin Machanda of Tufts University, who studies chimpanzee behavior at the Kibale Chimpanzee Project in Uganda, said the reserve had increased its safety precautions due to the pandemic.
“We are always wary of respiratory viruses,” he said, because those viruses are the leading cause of death in Kibale chimpanzees. Even the common human cold can be deadly.
Chimpanzees have suffered outbreaks of other coronaviruses. Normally, humans on Kibale maintain a minimum distance of two dozen feet from chimpanzees; that has been increased to 30 feet or more. Local workers have stayed on the reservation, instead of coming and going to their communities. And the project has reduced field study hours. All of these measures were led by the Ugandan government.
Tony Goldberg, a veterinarian at the University of Wisconsin, Madison, and director of the Kibale EcoHealth Project, said he has seen the devastation caused by respiratory diseases among chimpanzees. A deadly outbreak in 2013 on the reserve turned out to be the result of human rhinovirus C, the most common cause of the common cold worldwide. Until then, it had never been seen in chimpanzees.
“The last thing we need is for SARS-CoV-2 to move into an animal reservoir from which it could re-emerge,” said Dr. Goldberg.
Other researchers are studying species from beluga whales to deer mice for signs of the coronavirus. Kate Sawatzki, animal surveillance coordinator for a pet and other animal testing project at Tufts University Cummings School of Veterinary Medicine, said: “To date, we have analyzed 282 wildlife samples from 22 species, primarily bats. at rehab facilities in New England, and we are pleased to report that none have been positive. “
They have also tested 538 household pets, including those from households with people with Covid-19, and none have shown signs of an active virus. However, Dr. Sawatzki said, the lab also ran blood tests for antibodies, showing exposure, and there they found antibodies, as is common in humans. Pets appeared to be infected, but did not get sick or transmit the virus.
So far, the mink in Denmark is the only known case of the virus that infects an animal, mutates and is transferred to humans. Emma Hodcroft from the University of Basel, Switzerland, tracks various mutated versions of the coronavirus as it has spread across Europe and has reviewed scientific information released by Danish health authorities. He said he applauded the government’s decision to take swift action and sacrifice the mink: “Many countries have hesitated and waited before acting, and it can be incredibly damaging in the face of SARS-CoV-2, as we see.”
But he did not approve of the way the information was released, particularly at the government’s press conference on Wednesday, which warned of a serious threat to potential human vaccines but did not provide details on the concern. “The communication of science could have been much clearer and created fewer worries around the world,” said Dr. Hodcroft.
