WHO’s scenarios about the origins of Covid-19
Shanghai – A team of experts appointed by the World Health Organisation (WHO) completed its 28-day mission to the Chinese city of Wuhan this week seeking clues about the origins of Covid-19.
The following looks at their findings:
What are the main scenarios?
Peter Ben Embarek, the WHO’s leading animal disease expert, said the team conducted scientific investigations into four main scenarios about how Sars-CoV-2, the virus that causes Covid-19, spread into humans.
In the first, a single person was exposed to Sars-CoV-2 through direct contact with the host species, the horseshoe bat. The virus could have been circulating in humans for a while before making its breakthrough in heavily populated Wuhan.
The second scenario, seen as the most likely, involves transmission to humans via an as yet unknown intermediary species. Liang Wannian, an expert with China’s National Health Commission, said pangolins were potential candidates but other animals – including mink and even cats – may also be reservoirs.
A third possibility is that Covid-19 originated under the first or second scenarios and was then transmitted via cold-chain products. Chinese experts have attributed later Covid-19 clusters to imported frozen food and have raised the possibility it might also have caused the Wuhan outbreak.
The final scenario is that Sars-CoV-2 was leaked from the Wuhan Institute of Virology, which is known to have studied captive coronaviruses.
When did outbreak begin?
The experts said that while it was unlikely there were largescale outbreaks in Wuhan or elsewhere in China before December 2019, they do not rule out that it was circulating in other regions.
A crossover either directly from bats or from an intermediary species would suggest the transmission to Wuhan could have been facilitated by wildlife trading networks.
Marion Koopmans, another member of the expert team, said wildlife on sale in the Huanan seafood market could be traced to regions that contain bat habitats known to harbour viruses closely related to Sars-CoV-2.
One such region is the southwestern Chinese province of Yunnan, but the team is also considering that the first human transmission took place across the border in Laos or Vietnam.