In contrast to a lab-origin, the investigation by the WHO team now strongly suggests virus origin to a natural reservoir in bats, but unlikely to have been in Wuhan. The virus jumping directly from bats to humans is highly unlikely and initial investigation too suggests the introduction into humans through an intermediary host species.
By concluding that virus leak from a lab in the Chinese city of Wuhan, where SARS-CoV-2 virus first emerged, is “extremely unlikely” and did not require further study, a 17-member WHO international team along with Chinese counterparts have put to rest conspiracy theories early during the pandemic that suggested that the virus could have been bioengineered or might have escaped from a lab.
Genome sequence data and lab origin
While many scientists had dismissed the lab-origin theory, in mid-February 2020, a group of 27 prominent scientists from outside China went a step ahead and “strongly condemned conspiracy theories” in a letter published in The Lancet. The 27 researches said scientists who had analysed the genome sequence data of the virus shared by China and multiple countries “overwhelmingly conclude” that SARS-CoV-2, like many other emerging pathogens, had originated in wildlife. Even a year since the letter was published and after nearly half a million genome submissions have been made to a public database and analysed, scientists have not found any sign of direct human influence in the genetic structure of the virus.
Bats and intermediary host
In contrast to a lab-origin, the investigation by the WHO team now strongly suggests virus origin to a natural reservoir in bats, but unlikely to have been in Wuhan. The virus jumping directly from bats to humans is highly unlikely and initial investigation too suggests the introduction into humans through an intermediary host species. Wuhan, which is miles from any natural bat habitat, also makes the direct spillover from bats unlikely. The team has not been able to confirm the intermediary host.
Virus circulation in Wuhan
While early data suggest that the virus could have been circulating in Wuhan for several weeks before it was identified in the Chinese city, it asserts that there is no evidence of large outbreaks in Wuhan prior to December 2019. Chinese media reported in early March 2020 based on unpublished government data of a Hubei resident infected with the novel virus in mid-November. Also, in a study reported in The New England Journal of Medicine, scientists from the Chinese Center for Disease Control and Prevention found evidence of human-to-human transmission as early as mid-December 2019, which again suggests virus circulation weeks before they were identified in Wuhan. The Chinese authorities officially confirmed human-to-human transmission only in mid-January.
While the possibility of transmission of the virus via frozen food, a theory embraced by Chinese officials, has not been ruled out, the possibility of such a route appears unlikely as instances of live viruses on packaging have been “rare and isolated”.
Beginning of a long endeavour
This visit is just the beginning of a long endeavour to uncover the origin of the virus. It will succeed only when scientific investigation is allowed to follow its course without being politicised.
As in the case of the early 2003 SARS outbreak, China failed to be truly transparent and forthcoming with details early during the SARS-CoV-2 outbreak. It can partially undo the damage done by now being more open and cooperative in investigating the source of the virus so that future outbreaks of related coronaviruses can be identified and contained early if not prevented.
Science Chronicle 