In a pandemic that has so far affected 635 million people and killed 6.6 million, the origin of the Covid 19 pathogen continues to be of great interest. However, science is still hunting in the dark: According to the latest research results, SARS-CoV-2 viruses and bat viruses may have shared a common ancestor only a few years ago. But the details of the development remain in the dark, the British scientific journal “Nature” has now reported.
The 7th World One Health Congress was held in Singapore recently (November 8). There was also talk of the emergence of a pandemic that has been plaguing the world for more than two and a half years. Since at least the beginning of 2020, many teams of scientists—one hotspot being labs in Southeast Asia—have been busy sequencing the genetic material of more and more coronaviruses from different mammal species. In addition, there is deep-frozen tissue material with coronaviruses from years or decades past. Ultimately, this should create a family tree from which the origin of SARS-CoV-2 can be deduced without any doubt, and at the same time it would refute the repeatedly occurring and so far not verifiable speculations about the “escape” of SARS-CoV-2 from the laboratory.
A final solution is awaited
So far, science has put together many pieces of the puzzle about the origin of the Covid 19 pathogen, but the final solution is still missing. Australian author of the book “Nature” Smriti Malapaty, referring to research results presented at a conference in Singapore: “More than a dozen viruses closely related to SARS-CoV-2 have so far been isolated from bats and pangolins. To determine their genetic proximity to SARS-CoV-2 , often comparing whole genomes, each around 30,000 base pairs long. Using this method, researchers used a bat virus from Laos called BANAL-52 and a bat virus called RaTG13 from Yunnan in southern China to identify the closest relatives so far. The BANAL-52 genome is from 96.8 percent identical to SARS-CoV-2, the RATG13 genome of 96.1 percent.The difference of three to four percent indicates that the two viruses shared a common ancestor 40 to 70 years ago.
However, comparing the composition of complete genomes has one drawback: it does not take into account the rapid recombination with the exchange of individual sections of the genome between different types of viruses. That’s why evolutionary virologist Spyros Lytras and his team at the University of Glasgow analyzed 18 bat and pangolin viruses that are closely related to SARS-CoV-2, each in 27 parts. These genome fragments were each several hundred to several hundred thousand base pairs long. Each segment would have a different evolutionary history, Lytras pointed out.
“This analysis showed that some segments shared a common ancestor with SARS-CoV-2 several years ago. Most of these fragments pointed to a common origin around 2007. But a small segment of the genome of only 250 base pairs could point to a common ancestor.” ancestors in 2016, another 550-nucleotide fragment points to one in 2015. That would be three to four years before the emergence of SARS-CoV-2 in humans,” the Nature author wrote. Lytras would emphasize that primarily due to migration bats – with their harmless viruses – the occurrence of Covid 19 pathogens in southern China and Southeast Asia can be assumed.
However, whether the direct origin of SARS-CoV-2 will ever be determined remains controversial among virologists who study pathogen evolution. The recombination between viruses that takes place all the time in host organisms blurs the picture very quickly. Edward Holmes, a virologist at the University of Sydney: “The chances of this happening are almost nil. This steamer has left.” (a.p.a.)