Several weeks ago, we reported on the latest academic research regarding the coronavirus pandemic that claimed the virus had originated in the local bat population and was transferred to snakes, as an intermediary species, before being passed onto humans. Now, new research is claiming that the intermediary animal in the bat-human virus transmission pathway was not snakes, instead being the small and scaly, anteater-like Malayan pangolin.
At the time of writing, 614,000 people have tested positive for COVID-19 and the disease has claimed over 28,000 lives. Understanding the virus’ origins and genetic makeup is one of the most important avenues for scientists in both determining control measures and discovering effective treatments. The consensus in the scientific community is that bats are the natural reservoir of SARS-CoV-2 (the name of the specific virus from the coronavirus family which causes COVID-19) and that there was an intermediate host who had contracted the virus from bats before transferring it to the local human population in Wuhan.
Only a fortnight previous, genetic analysis and comparison of the virus’ DNA to a variety of species suggested that this intermediary animal was snakes; however, after several mistakes were discovered in the initial study, new research claims that the most likely intermediary host is the Malayan pangolin (Manis javanica).
In contrast to the previous research, this recent investigation utilised significantly larger animal DNA data sets and newer, more accurate bioinformatic methods to analyse the SARS-CoV-2 genome. The scientists found that protein sequences in the lungs of sick pangolins were 91% identical to the virus’ proteins in the lungs of human patients.
Furthermore, there were only five amino acid differences between the binding receptors of pangolins and humans, compared to the 19 differences between bats and humans –indicating that the virus resided in pangolins for a period of time before the recent coronavirus pandemic began.
This research greatly improves our understanding of the virus’ origins; however, we should consider that it is also possible that there may be other intermediary species for this disease. Coronaviruses are known to have multiple intermediate hosts, for example the 2003 outbreak of SARS-CoV had the palm civet (Paguma larvata), raccoon dog (Nyctereutes procyonoides) and ferret badger (Melogale moschata) as potential hosts. Additionally, although these protein sequences are 91% identical, this is not high enough to be considered as the same viral species – meaning that, at the least, they are evolutionary relatives rather than direct lineages of each other.
Whilst public health officials have praised this study for correcting faults in the scientific literature, arguably the most important part of this work is that it mitigates the time and resources that would have been wasted researching control measures and treatment that would have been based on incorrect knowledge of the intermediary species.
Chengxin Zhang, Wei Zheng, Xiaoqiang Huang, Eric W. Bell, Xiaogen Zhou, Yang Zhang. Protein Structure and Sequence Reanalysis of 2019-nCoV Genome Refutes Snakes as Its Intermediate Host and the Unique Similarity between Its Spike Protein Insertions and HIV-1. Journal of Proteome Research, 2020; DOI: 10.1021/acs.jproteome.0c00129
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