hi INDiA Copyright 2020
Coronavirus has a natural origin, says study
The study was published in the journal- Nature Medicine.
The analysis of public genome sequence data from SARS-Cov-2 and related viruses found no evidence that the virus was made in laboratory or otherwise engineered.
“By comparing the available genome sequence data for know coronavirus strains, we can firmly determine that SARS-CoV-2 originated through natural processes,” said the lead researcher Kristian Andersen.
In addition to Andersen, authors on the paper, “The proximal origin of SARS-CoV-s”, include Robert F. Garry of Tulane University, Edward Holmes, of the University of Sydney, Andrew Rambaut of University of Edinburg and W. Ian Lipkin of Columbia University.
Coronaviruses are a large family of viruses that can cause illnesses ranging widely in severity.
The first known severe illness caused by a coronaviruses emerged with the 2003 Severe Acute Respiratory Syndrome (SARS) epidemic in China. A second outbreak of severe illness began in 2012 in Saudi Arabia with the Middle East Respiratory Syndrome (MERS).
On December 31 last year, Chinese authorities alerted the World Health Organization (WHO) of an outbreak of a noval strain of coronavirus causing severe illness, which was subsequently named SARS-CoV-2.
As of February 20, 2020 nearly 167,400 COVID-19 cases have beed documented, although many more mild cases have likely gone undiagonsed. The virus has killed over 6,600 people.
Shortly after the epidemic began, Chinese scientists sequenced the genome of SARS-CoV-2 and made the data available to researchers worldwide.
The resulting genomic sequence data has shown that the Chinese authorities rapid detected the epidemic and that the number of COVID-10 cases have been increasing because of human to human transmission after a single introduction into the human population.
Andersen and collaborators at several other research institutions used this sequencing data to explore the origins and evolution of SARS-CoV-2 focusing in on several tell-tale features of the virus.
The scientists analyzed the genetic teemplate for spike proteins, srmatures on the outside fo human cells called ACE2, a receptor involved in regulating blood pressure.
The SARS-CoV-2 spike protein was so effective to binding the human cells in the fact, the scientists concluded that it was the result of natural selection and not the product of genetic engineering.
This evidence for natural evolution was supported by data on SARS-CoV-2’s backbone- its overall molecular structure. If someone where seeking to engineer a new coronavirus as a pathogen, they would have constructed it from the backbone of a virus known to cause illness.
But the scientists found that the SARS-CoV-s backbone differed subsstantially from those of already known coronaviruses and mostly resembled related viruses found in bats and pangolins.
“These two features of the virus, the mutations in the RBD portion of the spike protein and its distinct backbone, rule out laboratory manipulation as a potential origin for SARS-CoV-2,” said Anderson.
Josie Golding, PhD, epidemics lead at UK-based Wellcome Trust, said that the findings by Andersen and his colleagues are “crucially important to bring an evidence-based view to the rumours that have been circulating about the origins of the virus (SARS-CoV-2) causing COVID-19.”
‘They conclude that the virud is the product of natural evolution ending any speculation about deliberate genetic engineering,” Goluding added.
Based on their genomic sequencing analysis, Andersen and his collaborators concluded that the most likely origins for SARS-CoV-2 followed one of two possible scenarios.
In one scenario, the virus evolved to its current pathogenic state through natural selection in a non-human host and than jumped to humans.
This is how previous coronavirus outbreaks have emerged, with humans contracting the virus after direct exposure to civets (SARS) and camels (MERS).
The researchers proposed bats as the most likely resevoir for SARS-CoV-2 as it very similar to a bat coronavirus. There are no documented cases of direct bat-human transmission, howerever, suggesting that an intermediate host ws likely involved between bats and humans.
In this scenario, both of the distinctive feature of SARS-CoV-2’s spike protein-the RBO portion that binds to cells and the cleavage site that opens the virus up would have evolved to their current state prior to entering humans.
In this case, the current epidemic would be probably have emerged rapidly as soon as humans were infected, as the virus would have already evolved the features that make it pathogenic and able to spread between people.
In the other proposed scenario, a non-pathogenic version of the virus jumped from an animal host into humans and then evolved to its current pathogenic state withing the human population.
For instance, some coronovariuses from pangolins, armadillo-like mammals found in Asia nd Africa, have an RBD structure very similar to that of SARS-CoV-2. A coronavirus from a pangolin could possibly have been transmitted to a human, either directly or through an intermediary host such as civets or ferrets.
Then the other distinct spike protein characteristic of SARS-CoV-2 the cleavage site, could have evolved within ahuman host, possibly via limited undetected.
The researchers found that the SARS-CoV-2 cleavage site appears similar to the cleavagae sites of strains of bird flu that have been shown to transmit easily between people.
SARS-CoV-2 could have evolved such a virulent cleavage site in human cells and soon kicked off the current epidemic, as the coronavirus would possibly have become far more capable of spreading between people.
Study co-author ANdrew Rambaut cautioned that it is difficult if not impossible to know at this point which of the scenarios is most likely.
If the SARS-CoV-2 entered humans in its current pathogenic form from an animal source, it raises the probabiliyt of future outbreks, as the illness-causing strain of the virus coule sitll be circulating in the animal population and might once again jump into humans.
The chances are lower of a non-pathogenic coronavirus entering human population and then evolving properties similar to SARS-CoV-2