The disease first emerged in the city of Wuhan towards the end of last year – but much is yet to be discovered about the mechanism by which it did so. Last week a 57-year-old trader at Huanan seafood market was tentatively identified as the first person there to contract the illness, on December 10. However, she suggested she did so by using toilet facilities shared with wild meat sellers, meaning the search for Patient Zero – the first person infected after COVID-19 jumped species – continues.
The study, published in the scientific journal Nature, and co-authored by Yi Guan from the University of Hong Kong and Yan-Ling Hu from Guangxi Medical University in China, seeks to shed light on the mystery.
They write: “Although bats are likely reservoir hosts for SARS-CoV-2, the identity of any intermediate host that might have facilitated transfer to humans is unknown.”
Their research had identified COVID-19-related coronaviruses in Malayan pangolins (Manis javanica) which had been seized in anti-smuggling operations in southern China.
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Strikingly, a strain similar to the one which is now rampaging through the human population appears to have been present in five out of a total of 18 Malayan pangolins obtained from anti-smuggling operations in southern China between August 2017 and January 2018.
Additionally, they detected similar coronaviruses in three out of 12 additional animals seized in another Chinese province in 2018, and in another animal in a third province from which a sample was taken in 2019.
The viruses isolated have a sequence similarity of between 85 and 92 percent to SARS-CoV-2, the scientific name for the coronavirus which causes COVID-19.
One sample showed strong similarities in a region which encodes the “spike” of the virus, thereby facilitating entry into host cells.
None of the pangolin coronaviruses identified so far have a specific alternation in their sequences which is seen in human SARS-VoV-2, meaning the role the animals have playing in the transmission of the illness to humans remains unclear.
Nevertheless, the study authors highlight pangolins as the only mammals other than bats to date which have been found to be infected with a SARS-CoV-2-related coronavirus, suggesting they play an important role in the “ecology of coronaviruses”.
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Their report concludes: “The discovery of multiple lineages of pangolin coronavirus and their similarity to SARS-CoV-2 suggests that pangolins should be considered as possible hosts in the emergence of novel coronaviruses and should be removed from wet markets to prevent zoonotic transmission.”
Co-researcher Prof Edward Holmes of the University of Sydney added: “The role that pangolins play in the emergence of Sars-CoV-2 is still unclear.
“However, it is striking that the pangolin viruses contain some genomic regions that are very closely related to the human virus.
“The most important of these is the receptor-binding domain that dictates how the virus is able to attach and infect human cells.”
The pangolin is heavily hunted in China, both for its meat, and its skin and scales, which are used in traditional medicine.
Epidemiologists are keen to identify Patient Zero, the discovery of whom would offer vital clues about the origins of the outbreak and the way in which it has spread.
While the World Health Organization’s first press release about the subject, issued on January 5, indicated it first became aware of the illness on December 30, leaked Chinese Government data has suggested the first case was identified on November 17 at the latest, and possibly significantly earlier.
The study’s findings, specifically the confirmation that a strain closely related to SARS-CoV-2 was spotted in 2017, raises the possibility of the illness being in circulation significantly longer than previously believed.
Johns Hopkins University in the US put the total number of COVID-19 cases worldwide at 678,720 as of 12.50pm this afternoon, with 31,700 deaths.
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