Desi expert traces ‘great grandpa’ of SARS-CoV-2

The effort to trace the origins of SARSCoV-2, which causes Covid-19, would not have been as exacting had ‘patient zero’ been found by now. In January, the WHO said we might “never find who patient zero was”. But there was a way to identify the ancestor of the virus, a molecular epidemiologist from India found by “predicting” history with data. The ancestor, or progenitor genome, it turned out, had been around since at least October 2019 and survived till March 2020.


The progenitor is the genome of the coronavirus found in that one person who spread it to others, and then everyone else got descendants of that coronavirus. “Everyone was curious about new strains after December 24, 2019 (when the first case was reported). We wanted to know which strain came first, the progenitor,” Dr Sudhir Kumar, director of the Institute for Genomics and Evolutionary Medicine, Temple University, told TOI. “We can tell you the time of the ancestor’s origin was around or before October 2019.” Two months before the first case, predating by a wide margin the reference genome sequence that is being used now.



But the progenitor did not die. “We found it was still going around after the offspring started spreading. It was present in China in January 2020 and US in March 2020,” said Kumar, who is originally from Delhi. So, the ancestor virus didn’t need a mutation to spread. “It was ready to go on its own. SARSCoV-2 is its great-grandkid, three mutations away.”

To arrive at this, Kumar and his team adapted a process called mutation order analysis, often used to study mutations in tumours. The findings were published in the Oxford Academic journal ‘Molecular Biology and Evolution.