China’s secrecy, delay in reporting the outbreak in Wuhan, reluctance to allow quick and free access to the WHO team investigating virus origin, and the delay in finding the natural host or the intermediary has further fuelled the lab spillover hypothesis even in the absence of any compelling evidence.
Over 17 months after the World Health Organization first reported a cluster of cases of pneumonia of unknown cause in Wuhan, China, scientists are yet to determine with certainty how the SARS-CoV-2 virus, which is driving the pandemic, emerged.
Much like other viruses, SARS-CoV-2 too could have a natural origin after it jumped from animals to humans or could have somehow escaped from the coronavirus research lab located in Wuhan, the epicentre of the 2019 COVID-19 outbreak. While no hard scientific evidence is currently available to confirm the lab leak hypothesis, there are some scientific leads that support a natural origin.
If it is a zoonotic spillover, the virus could have either directly crossed over from bats to humans or through an intermediate host. But till date, neither the bat species that hosts the SARS-CoV-2 virus nor the intermediate host has been found. China’s secrecy, delay in reporting the outbreak in Wuhan, reluctance to allow quick and free access to the WHO team investigating virus origin, and the delay in finding the natural host or the intermediary has further fuelled the lab spillover hypothesis even in the absence of any compelling evidence.
Finding the host animal can be daunting. While the civet cat and dromedary camel were quickly identified to be the intermediate hosts of SARS and MERS, respectively, it took years to identify the horseshoe bat that harbours SARS virus strains. To date, a complete Ebola virus has never been isolated from an animal source.
If the virus had been bioengineered in a lab, the genome sequence would carry tell-tale signs of this. But till date, scientists have not found any signature of genetic manipulation. While a particular site (furin cleavage) on the SARS-CoV-2 spike protein that allows the virus to infect the cells has been cited as evidence of bioengineering, the fact is that it is not unique to SARS-CoV-2; other coronaviruses, including the one that cause common cold, have such a site.
A combination of nucleotides in the furin cleavage site that encode for a particular amino acid, another feature that is forwarded as supporting laboratory manipulation of the virus, too has been shown to be not unique. For instance, the nucleotide combination encoding for the amino acid is present in other sites of SARS-CoV-2 virus and in 2003 SARS virus. The possibility of SARS-CoV-2 evolving via cell culture appears bleak as scientists have found the virus losing features key to transmission and virulence unless cultured using new methods.
Reports of three researchers from the Wuhan lab falling ill in November 2019 by itself does not prove a lab leak hypothesis. There is no evidence so far that the researchers were infected with SARS-CoV-2 virus, and even if they were, it is necessary to prove that infection happened from inside the lab. In the absence of any conclusive evidence to support either hypothesis so far, a thorough investigation into both possibilities is needed.
While the inquiry by U.S. intelligence agencies might help provide vital clues, a scientific investigation is more likely to help reach closure; China’s cooperation, therefore, becomes vital and politicising the virus origin is not going to help.
Science Chronicle 