Faced with the rapid spread of the new coronavirus, scientists are racing against the clock to find clues about its epidemiology, which will help perfect both a vaccine as well as treatment and prevention pathways.
On February 7, researchers from Guangzhou, China, suggested that pangolins, long-snouted mammals, would be a very likely animal source from which the outbreak of 2019-nCoV, a new coronavirus that was detected in humans for the first time in last December in Wuhan. The proposal was based on the similarity of the genetic sequence of coronaviruses taken from animals and humans, which were 99% similar.
However, the same scientific team now rectifies. After a reexamination of the data, along with three other studies conducted on the pangolin coronavirus genome published last week, they have come to a new conclusion: Although the animal remains a contender, the mystery is far from solved.
So what was that 99% match referring to? What happened is that, in reality, the result did not refer to the entire genome, but was related only to the receptor-binding domain (RBD). The authors have explained this confusion in a new study published on February 20. In it, they attribute this misunderstanding to a serious lack of communication.
In the words of Xiao Lihua, a parasitologist at the South China Agricultural University and a co-author of the paper: “The press conference report was the result of an embarrassing lack of communication between the bioinformatics group and the study laboratory group” .
The receptor-binding domain or RBD is what allows them to latch onto and enter a cell. Therefore, it is a crucial part. But that two coronaviruses (pangolin and human) present such a high similarity does not mean that they are linked. To do this, the entire genome would have to be sequenced. There, apparently, the embarrassing misunderstanding resided.
According to Linfa Wang, a virologist at Duke National University Singapore School of Medicine, who was part of the team that discovered the origin of the SARS virus: “A 99% similarity between the RBDs of the two viruses is not necessarily enough. to link them ”.
What are scientists now saying about the pangolin as a host?
A subsequent genome-wide comparison found that the pangolin and human viruses share 90.3% of their DNA.
The three new studies on the pangolin genome published last week revealed that coronaviruses in pangolin cell samples shared between 85.5% and 92.4% of their DNA with the coronavirus found in humans.
Two other articles published on February 20, which also studied the coronavirus in pangolins, concluded that the viruses were between 90.23% 3 and 91.02% similar to the coronavirus that causes COVID-19.
A similarity that is not enough to identify the pangolin as a transmitting host and, of course, much less than the 99% reported in the February 7 study.
The example of SARS and civets
Let’s take an example of similar studies in another type of coronavirus: When the first case of SARS-CoV infection in humans was identified in 2002, scientists pointed to the civet (a carnivorous, cat-like mammal) as a transmitter of this type of coronavirus. coronavirus in humans. In this case, the SARS-CoV genome match in civets and humans was 99.8%, which is why it was considered as the host.
What do we know about the possible transmitting host of the new coronavirus?
So far, the closest match to human 2019-nCoV has been found in a bat in China’s Yunnan province. A study published on February 3 found that the bat coronavirus shared 96% of its genetic material with the virus that causes COVID-19.
Bats could have transmitted the virus to humans, but there are key differences between RBDs (allowing them to latch onto and enter a cell) in the two viruses. This suggests that the bat coronavirus did not directly infect people, but could have been transmitted through an intermediate host . For this host, a study published in January by the Journal of Medical Virology speculated on two common snakes in southeast China, the pluriband krait ( Bungarus multicinctus ) and the Chinese cobra Naja atra.
But there are no conclusive data, and this intermediate host is still unidentified.
Referencia bibliográfica:
Kangpeng Xiao, Junqiong Zhai, Yaoyu Feng, Niu Zhou, Xu Zhang, Jie-Jian Zou, Na Li, Yaqiong Guo, Xiaobing Li, Xuejuan Shen, Zhipeng Zhang, Fanfan Shu, Wanyi Huang, Yu Li, Ziding Zhang, Rui-Ai Chen, Ya-Jiang Wu, Shi-Ming Peng, Mian Huang, Wei-Jun Xie, Qin-Hui Cai, Fang-Hui Hou, Yahong Liu, Wu Chen, Lihua Xiao, View ORCID ProfileYongyi She. Isolation and Characterization of 2019- nCoV-like Coronavirus from Malayan Pangolins. Doi: https://doi.org/10.1101/2020.02.17.951335
