THEmikron puzzles the researchers. The genetic makeup of the new virus variant has changed so much that there is a large gap in the pathogen’s family tree: Despite the almost six million SARS-CoV-2 genomes that are now available, there are no intermediate levels.
Omikron has accumulated more than fifty mutations compared to the original SARS-CoV-2. There are currently three hypotheses about the origin of the new variant: The virus could have developed unnoticed for a year. It could have originated in an immunocompromised person or in animals. That would mean that SARS-CoV-2, which originally probably jumped from bats into humans via an intermediate host, would have jumped into another animal, would have adapted to the new host in order to get back into humans from there.
What sounds quite adventurous has already become reality: In April of last year, it became known that mink had been infected with SARS-CoV-2 through people in the Netherlands. Such cases were later reported in Denmark, Sweden, Italy, Spain, and the United States. The virus found ideal conditions in fur farms – a lot of animals in a confined space – and multiplied explosively. It was later proven that it jumped back into humans: SARS-CoV-2 had developed new mutations in the minks. Many fur farms had even developed their own genomic signature.
“This is worrying because there is a risk that new reservoirs will arise,” says virologist Marion Koopmans from the Erasmus MC in Rotterdam. “This can lead to an evolution of the virus that runs parallel to that in humans.” Over time, this could lead to deviant strains, which themselves become a new threat because they undermine the effectiveness of the vaccines. To prevent this risk, almost three million mink were culled in the Netherlands alone.
Several other animals have also been infected with SARS-CoV-2: The World Organization for Animal Health (OIE) had documented almost 600 transmissions in 14 types by the end of October. Including cats, dogs, hamsters, rabbits and many zoo animals, mainly big cats and great apes. in the Lincoln Children’s Zoo in Nebraska, three rare snow leopards died of Covid-19 in early November, and two hippos recently fell ill in Antwerp. The zookeeper noticed a thick nasal discharge.
Zoos are already vaccinating animals against Covid
Some animals can pass the virus on to one another; it is not known how often it can be transmitted back to humans. “The only confirmed retransmission is that from mink to humans,” says evolutionary biologist Sarah Otto from the University of British Columbia in Vancouver. “Possibly these are very rare occurrences.” According to a recent study, they became infected in 2020 a good four percent of domestic cats with SARS-CoV-2. As announced by the University of Veterinary Medicine Hannover, a total of 2160 blood samples from cats from Germany, the United Kingdom, Italy and Spain were examined. At this early stage of the pandemic, humans were the only possible source of infection. Cats rarely get sick, but they can shed the virus. According to the researchers, however, there is no evidence that cats contribute to the spread and infect humans again.
“SARS-CoV-2 can easily jump over the species barriers”, says veterinarian Fabian Leendertz, director of the newly founded Helmholtz Institute for One Health in Greifswald. “The question is, where does it happen and in what way.” Two hippos in the zoo are easy to isolate. Some zoos in the United States have already started vaccinating their animals against Covid-19. Zoetis, a company spun off from Pfizer, has developed a vaccine specifically for animals.
But if SARS-CoV-2 spreads in large animal populations living close together, things will look different. Then the pathogen would have other hosts in addition to humans, in which it can multiply en masse, which increases the risk of virus variants. “In this case, diversity poses a danger,” says Leendertz.