In my post from 23 December 2021, I presented data that link the current COVID-19 pandemic with pangolins. I wrote that one of the ‘candidates’ that may served as a host for the SARS-CoV-2 virus to jump from bats to humans may have been Malayian pangolins (Manis javanica) also due to their closer proximity to humans. The primary study I made reference to was that of Lam et al. (2020) who demonstrated that a large percentage of trafficked pangolins contained coronaviruses. Since they are furthermore one of the most trafficked species in the world (Challender et al. 2014), it appears rather easy to put the blame on them.
Indeed, also the question of natural origin of the virus has been challenged due to problems in the applied methodology for genome sequencing. While one of the first papers published on this issue – Zhou et al. 2020 – has shown that there is a 96.2% overlap of the genome of the current coronavirus with found coronaviruses in bats, Deigin & Segreto (2021) challenge the overall findings of Zhou et al., not necessarily because they are proven wrong, but rather because there have been problems in the datasets – collection and interpretation – themselves.
Pangolins and their role in the current pandemic
As mentioned, a key paper ascribing the COVID-19 pandemic a natural origin is Zhou et al. (2020). In this paper, the authors rely on genetic data collected from bats. While the natural origins themselves are not necessarily challenged, it remains in the dark how and where some of the data was collected. At the same time, some of the sequencing, as an Addendum to the original article clarifies, was done already in 2018, meaning prior to the outbreak of the pandemic. This, as Deigin & Segreto contest, raises issues as regards the interpretability of the data.
Be that as it may – as a non-virologist this is impossible to fully comprehend – a second paper was published in 2019 which links coronaviruses with pangolins (Liu et al. 2019). As a consequence, pangolins were considered a potential threat when entering the international trade chains. This was because also other studies, such as Andersen et al. (2020) took up the findings of Liu et al. yet without noticing that the same dataset that Liu et al. referred to served as the same dataset for other studies as well, thereby establishing the pangolin as a corona-spreader even more. What added to this problem was that some elements of the dataset were altered, and published as unaltered data elsewhere (see e.g. Liu et al. 2020; Xiao et al. 2020). All of these studies were flagged as having somewhat flawed data. Especially the finding of Chan & Zhan (2021) that some of the samples stemmed from merely from two pangolins out of 13 and that this was not adequately flagged by the authors of the original studies proved to be problematic. However, after careful examination, journals such as PloS Pathogens decided that despite the utilisation of the same data in other studies, “the article’s conclusions are valid and are supported by the results, although aspects of the study were not adequately reported in the original publication” (Liu et al. 2021). Also Nature allowed for an Author Correction and an Addendum in which several of the addressed issues were seemingly cleared.
While the above refers to the genetic elements of the virus, another elements refers to the actual trade in pangolins, their potential to spread the virus even further and the role of the Wuhan market. In a study on the spread of ticks that was carried out between 2017-2019, Xiao et al. (2021) found that neither pangolins nor bats were traded on the Wuhan market. While most of the wildlife trade at the market was basically illegal, the authors are confident that given the traders’ openness there would not have been a logical reason to conceal trade in pangolins or bats. This goes somewhat hand in hand with Chan & Zhan’s finding of the characteristics of the coronavirus found in pangolins being so rare and unique that it is much more likely that they were not the immediate vectors, but rather got infected along the illegal trade chain (Chan & Zhan, 2020). This means that it is very possible that the source (or vector) of the virus is one or are several other species and that pangolins have been caught in the crossfire, so to speak.
While pangolins still remain a contender in the discussions surrounding the origin of the SARS-CoV-2 virus, the mystery is far from solved. Placing the blame on one species may cause unprecedented killings, as could be seen in the culling of 17 million minks in Denmark (e.g. BBC News, 2020) or the killing of civets in China over fears of SARS in 2004 (CBS News, 2004). From a human health perspective, a conservation perspective and an animal welfare perspective, finding the origins of the SARS-CoV-2 virus is therefore imperative. Relying on peer-reviewed studies is the only way for laypersons to gather proper information. If these studies turn out to be flawed, the trust in the scientific method becomes yet another victim of this pandemic.
- Andersen, KG, A Rambaut, WI Lipkin, EC Holmes & RF Garry. (2020). The proximal origin of SARS-CoV-2. NatureMedicine 26, 450-455. (here).
- BBC News (2020). Covid: Denmark to dig up millions of mink culled over virus. BBC News, 21 December 2020. (here)
- CBS News (2004). Civet cat slaughter to fight SARS. CBS News, 11 January 2004. (here).
- Challender, DWS., C Waterman & JEM Baillie. (2014). Scaling up pangolin conservation. IUCN SSC Pangolin Specialist Group. (here).
- Chan, AY , & Zhan, HS (2020). Single source of pangolin CoVs with a near identical Spike RBD to SARS‐CoV‐2. BioRxiv. (here).
- Deigin, Y & R Segreto (2021). SARS‐CoV‐2′s claimed natural origin is undermined by issues with genome sequences of its relative strains. Bioessays 2021. (here).
- Lam, T-Y, M H-H Shum, H-C Zhu, Y-G Tong, X-B Ni, Y-S Liao, W Wei, W Y-M Cheung, W-J Li, L-F Li, GM Leung, EC Holmes, Y-L Hu & Y Guan. (2020). Identifying SARS-CoV-2 related coronaviruses in Malayan pangolins. Nature 583, 282–285. (here).
- Liu, P , Chen, W , & Chen, JP (2019). Viral metagenomics revealed Sendai virus and coronavirus infection of Malayan Pangolins (Manis javanica). Viruses, 11(11), 979. (here).
- Liu, P, Jiang, JZ , Wan, XF , … & Chen, J (2020). Are pangolins the intermediate host of the 2019 novel coronavirus (SARS‐CoV‐2)? PLoS Pathog, 16.
- Liu, P, Jiang JZ, Wan, XF … & Chen, J (2021). Correction: Are pangolins the intermediate host of the 2019 novel coronavirus (SARS-CoV-2)? PloS Pathog. (here).
- Xiao, K , Zhai, J , Feng, Y , Zhou, N, … & Shen, Y (2020). Isolation of SARS‐CoV‐2‐related coronavirus from Malayan pangolins. Nature, 583, 286–289. (here).
- Xiao, X, C Newman, CD Buesching, DW Macdonald & Z-M Zhou (2021). Animal sales from Wuhan wet markets immediately prior to the COVID-19 pandemic. Scientific Reports 11. (here).
- Zhou, P, X-L. Yang ….Z-L Shi. (2020). A pneumonia outbreak associated with a new coronavirus of probable bat origin. Nature 579, 270–273. (here).