In recent research published in Nature Microbiology, findings confirm that SARS-CoV-2, also known as the novel coronavirus, has silently been circulating in bats for several decades. The study marks bats as the ‘primary reservoirs’ of the virus, suggesting divergence from closely related bat viruses approximately 40-70 years ago. This article explores the depth of this study and challenges traditional assumptions about the origin and transmission of the virus.
Decoding the Divergence
Confirming suspicions raised by a prior Chinese study, the current research reveals the likely timeline for the divergence of SARS-CoV-2 and related bat viruses. According to the Chinese study, the virus that causes Covid-19 is closely affiliated with RaTG13, a virus discovered in a horseshoe bat from Yunnan province in 2013. The almost 96% genome identification similarity between these two viruses suggests that the genesis of Covid-19 likely stems from bats. Crucially, evidence reveals that SARS-CoV-2 did not result from recombination of any other sarbecovirus, an assertion that explicates the distinctive characteristics of this virus.
Understanding Recombination
Recombination refers to the process where fragments of DNA are broken and rearranged to produce variant gene combinations. This process cultivates genetic diversity at the gene level, reflecting variances in the DNA sequences of different organisms. Interestingly, the virus’s ability to bind to human receptors (specifically Angiotensin-Converting Enzyme 2 (ACE2)) via the spike protein developed within bats. This trait is not a recent acquisition through recombination but is shared ancestrally with bat viruses.
Uncovering A Single Lineage
The study indicates the existence of a ‘single lineage’ circulating among bats, possessing properties sufficient to infect human cells. Similar traits were also discovered in bat sarbecoviruses linked to the 2002 Severe Acute Respiratory Syndrome (SARS) lineage.
Study Methodology
Researchers analysed the evolutionary history of SARS-CoV-2 through genomic data on sarbecoviruses. Three approaches were employed to identify virus regions that had not undergone recombination, which were instrumental in tracing its evolution. The findings suggest that RaTG13 and SARS-CoV-2 share a single ancestral lineage, with an estimated genetic divergence from related bat sarbecoviruses taking place around 1948, 1969, and 1982.
Challenging Established Assumptions
The research contradicts prevailing beliefs about pangolins acting as intermediate hosts for the virus – facilitating its transition into humans. While there’s still a possibility of pangolins being a medium for transmission, no evidence has surfaced to confirm pangolin involvement in adapting the virus to affect humans. Current data aligns with the theory that the virus evolved in bats, enabling replication in the upper respiratory tracts of both humans and pangolins. Similarly, theories about snakes serving as intermediate hosts for SARS-CoV-2 have also been debunked by this study.
Raising Concerns
The lengthy divergence period signals the potential existence of other undocumented virus lineages in horseshoe bats, which could potentially leap from bats to humans. Unfortunately, due to inadequate sampling, it remains uncertain as to how many additional lineages there may be. The dynamic process of recombination amongst lineages in the bat reservoir further complicates the identification of viruses.
A Global Approach to Mitigation
To successfully identify these viruses and their respective lineages, a comprehensive global network of real-time human disease surveillance systems is paramount. Such measures would enable efficient pathogen identification and characterisation, ultimately aiding in the aversion of future pandemic situations.