SARS-CoV-2: Manmade Menace or Unfortunate Turn of Evolution?

A natural but an unfortunate turn of evolution, God's or mother nature's wrath, a faulty laboratory leak, or outright bioweapon – the global pandemic of COVID-19 brings about all sorts of theories. Can science offer us some answers on the origin of this virus?

From an unfortunate escape from laboratories to intentional release as a bioweapon, we all must have heard some conspiracy theories about the origin of the novel coronavirus. Many people firmly believe that the virus behind the current pandemic is anything but natural. While finding the answer to this question would hopefully satisfy the many people wondering about the origin of SARS-CoV-2, understanding the origin of the virus is vital to understand better the emergence of new pathogens and possible exposures¹.

So far, several studies have focused on the origin of the coronavirus. The very first pivotal study on this topic emerged in March 2020 in the Nature Medicine Journal². Based on the less-than-ideal interaction of SARS-CoV-2 with human ACE2 receptors, their high-affinity binding is most likely the result of a natural selection that permits another optimal binding solution to arise. Moreover, the genetic data irrefutably showed that SARS-CoV-2 is not derived from any previously used virus backbone, which would have pointed to genetic manipulation. Taken together, this was considered strong evidence that the virus is not the product of purposeful manipulation².

Another study was published a few months later, which focused on the evolutionary origins of SARS-CoV-2³. These estimates suggest that the lineage giving rise to SARS-CoV-2 has been circulating unnoticed in bats for decades. However, coronaviruses have a high recombination rate, which makes inferring reliable evolutionary histories difficult³. 

Recently, WHO published a report on the origin of SARS-CoV-2⁴. An international team of experts examined various scenarios for the introduction of the virus. They considered four scenarios – a direct zoonotic transmission to humans (animal1-human) – a spillover, introduction through an intermediate host followed by spillover (animal1-animal2-human), introduction through the cold food chain, or a laboratory incident. Based on their assessment, the most likely pathway is animal1-animal2-human, followed by a direct animal1-human way. The introduction of the virus through the cold food chain is considered a possibility; on the other hand, it is considered extremely unlikely that the emergence of the virus happed as a laboratory incident⁴.

The animal source of the virus is not clear. SARS-CoV-2 is similar to a coronavirus identified in horseshoe bats (Rhinolophus species) and to a lesser extent to a strain isolated from pangolins. However, neither of the viruses identified so far is sufficiently similar to SARS-CoV-2 to serve as its direct progenitor. The high susceptibility of mink (read more) and cats to SARS-CoV-2 suggests that additional species may act as a potential reservoir. Moreover, the presence of SARS-CoV-2 has not been identified in tested bats or wildlife, livestock, and poultry samples across China. No evidence of animal infections was found in tested animal products in the Huanan market. The Huanan market is commonly believed to be the outbreak's source, though no firm conclusion could be drawn about that either⁴.

There was also the question of the start of the outbreak - is it possible that the virus circulated long before we identified the first cases? The findings suggest that circulation of SARS-CoV-2 preceded the initial detection of cases by several weeks. However, based on the molecular sequence data, the outbreak most likely started no earlier than between mid-November and early December 2019⁴.

In conclusion, even after this vigorous investigation, there is still a lot of uncertainty about the SARS-CoV-2. Understanding the origin of the virus is essential, and because this initial study did not answer the big question, further studies are required.

So, where do we go from here? Further research plans to focus on various aspects that could help elucidate the issue. These include testing donated blood from 6 months before the first known cases, identifying wildlife farms supplying markets in Wuhan, and assessing how long the virus can persist in frozen foods that might have also been a source of transmission. Although the chances of COVID-19 having originated in a lab accident are slim, this possible route will also undergo a more comprehensive inquiry⁵. However, even with more research, we may never have a definite answer to the origin of SARS-CoV-2.

References

1. https://www.who.int/news/item/30-03-2021-who-calls-for-further-studies-data-on-origin-of-sars-cov-2-virus-reiterates-that-all-hypotheses-remain-open
2. Andersen, K.G., Rambaut, A., Lipkin, W.I. et al. The proximal origin of SARS-CoV-2. Nat Med 26, 450–452 (2020). https://doi.org/10.1038/s41591-020-0820-9
3. Boni, M.F., Lemey, P., Jiang, X. et al. Evolutionary origins of the SARS-CoV-2 sarbecovirus lineage responsible for the COVID-19 pandemic. Nat Microbiol 5, 1408–1417 (2020). https://doi.org/10.1038/s41564-020-0771-4
4. https://www.who.int/health-topics/coronavirus/origins-of-the-virus
5. Mallapaty S. After the WHO report: what's next in the search for COVID's origins. Nature. 2021 Apr;592(7854):337-338. doi: 10.1038/d41586-021-00877-4. PMID: 33790440.

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