Over 17 months after WHO 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 emerged. Much like other viruses, SARS-CoV-2 too could have a natural origin or somehow escaped from the coronavirus research lab in Wuhan, the epicentre of the COVID-19 outbreak. With no hard scientific evidence 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 and delay in reporting the Wuhan outbreak and in finding the natural host or the intermediary have further fuelled the lab spillover hypothesis. 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, the genome sequence would carry tell-tale signs. But 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. 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 — too has been shown to be not unique. For instance, the nucleotide combination encoding for the amino acid is present in other sites of the SARS-CoV-2 virus and in the 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 Wuhan lab researchers falling ill in November 2019 by itself does not prove a lab leak hypothesis. There is no evidence that they were infected with the SARS-CoV-2 virus, and even if they were, it is necessary to prove that it happened from inside the lab. In the absence of conclusive evidence to support either hypothesis so far, a thorough investigation is needed. While the inquiry by the U.S. intelligence might provide 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.