The three hypotheses of scientists about the origin of the omicron variant: the reverse zoonosis theory

• Covid What if omicron was the variant that science was waiting for?

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Ever since South African scientists announced that they had identified a disturbing new variant, later named

by the World Health Organization, the world has been anxiously waiting to find out how dangerous this new variant really is, what impact it will have on the pandemic and the vaccines.

But there is another question that scientists around the world are asking: where does

come from

?

For now, scholars are formulating hypotheses and it is not taken for granted that some day light will really be shed on the origin of a variant with such strange characteristics.

Evolution under the radar

It seems pretty obvious that omicron was not developed from one of the previous worrying variants, such as

or

.

In fact, omicron is very different from the millions of

genomes

that have been shared over the months.

Based on the genetic profile,

, a virologist at the University of Bern, speculates that omicron may date back to mid-2020, she writes in

.

It seems that omicron

.

"It is difficult to find a close relative of hers, it probably soon separated from the other strains", comments the virologist.

The three hypotheses

But where have omicron's predecessors been hiding for over a year?

There are three possible explanations according to the scientists.

The reverse zoonosis hypothesis

Some scientists think that the virus may have hidden in

or other animals rather than humans, and therefore suffered various

that led to new mutations before returning to humans.

Kristian Andersen

, an immunologist at the Scripps Research Institute, is among those who have hypothesized that omicron may have arisen from a

(a zoonotic event is when an animal pathogen begins to spread to humans and a reverse zoonosis is when this virus returns to an animal species).

"I know most scientists think," Andersen said, "that the variants come from immunosuppressed individuals, and this is plausible. But to be honest, I think a new zoonosis is more likely considering that many mutations are somewhat unusual and that the strain appears to have undergone early division from other

variants

. This possibility should not be ruled out. "

Adaptation to rodents

According to research by

, professor of microbiology and immunology at the Tulane School of Medicine, omicron has

.

Other variants like Alpha, for example, carry only some of these mutations.

In addition to 'rodent adaptation' genetic mutations, omicron produces a number of changes not seen in any other version of

, and many scientists see this as potential evidence that the variant arose in an animal. invited.

The case of the white-tailed deer

"It's interesting to note how incredibly different omicron is from the other variants," says evolutionary biologist

of the University of Arizona in Tucson in

, noting that 80% of

sampled in Iowa between late November 2020 and early January 2021 were carriers of Sars-CoV-2.

There may be, some scientists speculate, other animal species, in addition to the white-tailed deer, also chronically infected and this could lead to selective pressure over time.

A study published a month ago suggests that the

could become what is known as a reservoir for Sars-CoV-2: Animals can carry the virus indefinitely and periodically transmit it to humans.

"If this is the case, it would destroy any hope of eliminating or eradicating the virus in the United States and therefore the world," says

Penn State

veterinary virologist

, who co-led the study.

"It is too early to rule out any theory about the origin of omicron," says

, an evolutionary biologist at the University of Oxford, who is skeptical of the animal scenario given the high number of human infections.

"I would start to worry more about the animal reservoirs if we could kill the virus and then I could find a place to hide in the animals."

Hunting omicrones in animals

Scientists are already examining several animal species to see if they can be infected with

and looking for traces of omicron. To understand whether omicron could actually be the result of reverse zoonosis,

suggests experimenting with selected species of wild animals to see if they can become infected and, once infected, if patterns of viral evolution similar to those seen in omicron occur.

One of the distinguishing characteristics of

is that, as described by virologists, it is a promiscuous virus capable of infecting several species, including

And given the ease with which the virus appears to pass from one species to another, the list of animals capable of harboring the coronavirus is likely to grow.

The hypothesis of poor viral surveillance

Other scientists, such as

, a virologist at the Charité University Hospital in Berlin, support the theory that omicron has been circulating "dormant" for quite some time.

"I guess this new strain did not evolve in South Africa, where a lot of sequences are being produced, but somewhere else in southern Africa during the winter wave."

Andrew Rambaut, an evolutionary biologist

at the University of Edinburgh, believes that the virus is unlikely to have remained hidden in a group of people for so long: "I'm not sure there really is a place in the world isolated enough to allow this type of virus to spread, spread for a long time before it spreads in other areas. "

The chronic infection hypothesis

Instead, Rambaut and several other scientists suggest that the virus most likely developed in

, likely someone whose immune response has been compromised by another disease or drug.

When Alpha was first discovered in late 2020, it appeared to have acquired numerous mutations at the same time, leading researchers to speculate that it was the result of a chronic infection.

A case of an HIV-infected woman has been documented in South Africa.

The virus has accumulated a series of mutations observed in the variants of interest.

Immunosuppressed people could act as a "reservoir" of variants, since they can harbor the virus for several weeks, long enough to mutate.

According to the criteria of The Trust Project

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