Scientists Believe Animals Might Indeed Spread New Variants Back To Us


  • More than 5.7 million humans have died from COVID-19 globally, over two years.
  • The list of infected zoo animals now includes gorillas, cougars, otters, spotted hyenas, and hippos.
  • Scientists concluded that it did not derive from any of the other variants, but, rather, it seemed to have evolved along its own trajectory.

SARS-CoV-2 has been easily spread from humans to other species during the pandemic. Animals, according to some experts, may be able to spread new versions back to humans as reported by New Yorker.

Genetically diverse

Last Thanksgiving, Rilu, an eleven-year-old snow leopard and father of seven, began sneezing and wheezing.

Snow leopards are native to the Himalayas, but Rilu was born in a zoo in Oklahoma City, then moved to the Miller Park Zoo, in Illinois, in 2011, to form part of the Species Survival Plan—the zoos’ matchmaking effort to maintain a genetically diverse “insurance” population of endangered animals.

A PCR test in early December confirmed that Rilu had covid-19.

He developed pneumonia and grew weaker, despite various attempts at treatment.

On January 6th, he became the fifth captive snow leopard in the United States to die from covid-19 complications within three months.


Because ancestral sars-CoV-2 initially evolved in bats, then somehow found its way into humans, it is called a “zoonosis”—a disease that transmits from animals to us.

Roughly seventy-five per cent of all emerging infectious diseases are zoonoses.

But, as scientists learned in the early months of the pandemic, sars-CoV-2 transmits easily back to other species.

“I can’t think of any single zoonotic virus with an equivalently broad host range,” Barbara Han, a disease ecologist, told me.

First, there were pet dogs and cats, then tigers and lions at the Bronx Zoo.

The list of infected zoo animals now includes gorillas, cougars, otters, spotted hyenas, and hippos.

Sterilization program 

Most recently, on February 7th, scientists at Penn State posted a paper (not yet peer-reviewed), revealing that the Omicron variant was widespread among white-tailed deer on Staten Island. 

(The blood and nasal samples came from a sterilization program underway to control the borough’s deer population.)

Evidence from antibody analysis suggests they might even be susceptible to reinfection, which would indicate the species’ potential as a sars-CoV-2 reservoir—a distressing thought, considering that their population numbers roughly thirty million and they thrive among humans.

“The sort of hidden exposure of the virus in animals is the most alarming part of this whole process.”

“We were hoping to end this pandemic by, you know, vaccinating everybody,” Kuchipudi told me.

Other variants in humans

Reverse zoonosis might explain where Omicron came from.

After it emerged in November, in South Africa, the scientists who sequenced its genome quickly saw something strange.

Scientists concluded that it did not derive from any of the other variants, but, rather, it seemed to have evolved along its own trajectory.

In December, Wenfeng Qian, a Beijing-based scientist, and a group of his colleagues offered a possible answer: mice.

In a paper published in the Journal of Genetics and Genomics, they argued that Omicron’s mutations had been subjected to greater pressure to evolve than the other sars-CoV-2 variants, which had evolved in human hosts—indicating, perhaps, that it had evolved in a different species.

Infected mice

How infected mice might have infected people is anyone’s guess.

Trevor Bedford, a professor at Fred Hutchinson Cancer Research Center in Seattle, and a leading expert on viral evolution and surveillance said that Qian’s paper “is the most compelling case for rodent origin I’ve seen.”

But Bedford favours a more popular hypothesis—that Omicron evolved in a chronically infected, immunocompromised patient, such as someone who is H.I.V.-positive. 

“I’d place more likelihood on the chronic infection route,” he wrote in an e-mail, “but definitely not certain of this origin.”

Reverse transmission

Omicron most likely evolved to its current form in South Africa, where it was first detected, or somewhere in the wider region, where both vaccination rates and disease surveillance are low until it began rapidly infecting people in South Africa.

And yet, its geographic origin remains unclear, Marietjie Venter, a South African researcher and the chair of sago, told me.

She added that they later found that the variant was already circulating in Europe by the time her group detected it.

In any case, “at the moment,” Venter said, “the hypothesis of reverse transmission to a mouse is interesting but at this stage theoretical.”

It’s based only on the analysis of mouse strains in labs, not on the detection of Omicron in wild mice.

Disease surveillance

This could be because disease surveillance in wild animals is challenging if it happens at all.

But whether a mouse could transmit a sars-CoV-2 variant to humans is unknown. 

“Airtight evidence of that nature is typically very difficult to come by,” Han said.

Until recently, there had been only one known secondary spillover event—when sars-CoV-2 was found to have infected mink and spread like wildfire on fur farms across Europe; later, in the Netherlands, the virus was transmitted from mink back to farmers.

Thousands of mink were culled, farms were shuttered, and the fur industry was destroyed.

“With wildlife—unmonitored, mostly unseen—anything is possible.”

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Source: New Yorker


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