Mumbai: While the origins of the pandemic-causing SARS-CoV-2 virus are still hotly debated, a group of Indian scientists is certain rodents played a role in “creating” Omicron, the last COVID-19 variant to emerge 17 months ago.
A paper in this regard by India’s senior virologist Dr T Jacob John, formerly at Christian Medical College in Vellore, and Dr Dhanya Dharmapalan from Apollo Hospital in Nerul was published in ‘Current Science’, a peer-reviewed journal published by the Indian Academy of Sciences, on Monday.
The reason for focusing on the Omicron variant is simple, it is the ‘longest running’ COVID variant, with 1,100 sub-variants and recombinants. “This variant behaves like a new virus subtype, and the infections caused are so different (from the original Wuhan variant) that it deserves to be called COVID-21,” said the doctors.
When Omicron emerged in Botswana and South Africa in November 2021, scientists felt it was due to persistent COVID infection of seven to nine months in persons with immune-compromised state (say, HIV). “But a British study in HIV-positive persons showed the rate of mutations was fairly low,” Dr John told.
Omicron had more mutations on the spike protein gene (that allow viruses to penetrate host cells) than other variants. Within a few weeks of its emergence, South African doctors noted it had “high efficiency” in transmission, could evade vaccines, but caused a mild disease and fewer deaths.
Dr John favours the rodent theory because of Omicron’s different structure as well as the fact that mutations could occur faster in another animal than humans. “Chinese researchers have previously investigated and reported that rodents were the animal hosts,” he said. The theory is that reverse zoonosis (when a disease is transmitted from humans to animals) took place and a mutated variant returned to infect humans. A paper from Finland showed the house mouse was susceptible to the Beta variant of SARS-CoV-2, spread by the “nasal route”, and could spread it to all cage mates.
Dr Dharmapalan said one research paper showed hamsters (another type of rodents) imported from the Netherlands by a pet store in Hong Kong were tested after its owner was diagnosed with the Delta variant. “On further investigation, other visitors to the pet shop were also found to have Delta. Therefore, it is inferred that reverse zoonosis with SARS-CoV-2 infection had occurred in this hamster colony in the Netherlands, followed by hamster-to-hamster spread and subsequently zoonotic spread from them to human subjects,’’ said Dr John.
The doctors said Omicron’s high transmissibility is possibly due to its preference for a different pathway than other variants to infect cells. This way it has a 70-fold potential to infect bronchial cells than alveolar cells of lungs.
The doctors ruled out another COVID wave. Omicron established ‘herd immunity’ as it infected over 90 per cent of the population in many countries, and brought the pandemic to an end in India in February 2022.
However, in the future, Omicron’s sub-variants will continue to cause a surge in cases from time to time. “We expect Omicron as the sole survivor of the endemic SARS-CoV-2 infection and consequent disease,’’ said Dr John, advising vaccination.
Is there a possibility of eradicating SARS-CoV-2? “With the emergence of Omicron illustrating that SARS-CoV-2 is no longer exclusively human, the probability of eradication is rated very low.”