Two years after the first case of Covid-19 was recorded, scientists are still struggling to identify the original source of the virus.
Many scientists believe the virus was transmitted from a bat to a human after emerging from the wild, sparking new fears that more animal-to-human transmission could happen in the future — and unleash pandemics even more deadly than Covid.
According to the US Centers for Disease Control and Prevention, humans can spread Covid to animals during close contact but the risk of animals transmitting it to people is low.
Since Covid emerged, many types of animals have gotten infected, including pet cats, dogs and ferrets; zoo animals such as big cats, otters and non-human primates; farm-raised mink; and white-tailed deer.
“Around the world, we might have animals potentially incubating these variants even if we get (Covid-19) under control in humans,” David O’Connor, a virology expert at the University of Wisconsin-Madison, said.
“We’re probably not going to do a big giraffe immunisation program any time soon.”
Mr O'Conner is one of twenty authors who wrote a paper linking animals to the spread of the virus.
Dr Michael Worobey, an evolutionary biologist at the University of Arizona who also contributed to the paper, published a Covid-19 timeline in November, linking the first known human case to the Huanan Seafood Wholesale Market in Wuhan, China, where live animals are sold.
He said he has been looking for genetic fingerprints that might indicate whether the Omicron variant was created when the virus jumped from humans to an animal, mutated, and then leaped back to people.
He said the theory the virus was first transmitted by an animal is more likely than it being leaked from a Chinese lab which some have theorised, although he acknowledges both are viable theories.
“The lab leak idea is almost certainly a huge distraction that’s taking focus away from what actually happened,” Dr Worobey said.
He said the research made him even more confident about the animal hypothesis, which is “just way more supported by the data”.
Covid-19: The ninth documented coronavirus to infect humans
According to the study published in Cell, all previous human coronaviruses have zoonotic origins, as have the vast majority of human viruses. The paper states that Covid-19 is the ninth documented coronavirus to infect humans.
"The emergence of SARS-CoV-2 bears several signatures of these prior zoonotic events. It displays clear similarities to SARS-CoV that spilled over into humans in Foshan, Guangdong province, China in November 2002, and again in Guangzhou, Guangdong province in 2003," the study reads.
"Both these SARS-CoV emergence events were associated with markets selling live animals and involved species, particularly civets and raccoon dogs that were also sold live in Wuhan markets in 2019."
The authors of the paper said failure to look into investigating the animal origin of the virus “would leave the world vulnerable to future pandemics arising from the same human activities that have repeatedly put us on a collision course with novel viruses”.
Experts say preventing zoonotic disease will require not only cracking down on illegal wildlife sales but making progress on big global problems that increase risky human-animal contact, such as habitat destruction and climate change.
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