Dr Felix Drexler, from the Institute of Virology at the University of Bonn Medical Centre and the German Centre for Infectious Disease Research, led a session at the AMP Europe Congress 2021. This article summarises his presentation, which discussed the evolutionary origin of SARS-CoV-2 and the possible trajectory of COVID-19 in the future.
Are bats the main culprit?
The evolutionary origin of COVID-19 has been a topic of conversation across the globe for over a year now. However, it is not widely recognised that COVID-19 is just one of many coronaviruses that can infect humans. In fact, there are four ‘common cold’ coronaviruses and three emerging coronaviruses – SARS-CoV, MERS-CoV and SARS-CoV-2.
Over 60% of human pathogens are zoonotic. These are infectious diseases that can spread between a non-human animal to humans – and vice versa. Dr Drexler explained: “In terms of the origin of SARS-CoV-2, bats are the incriminated culprits. And there have been many meta-analyses to suggest that bats are ‘special’ when it comes to spreading diseases”.
Bats have been phylogenetically determined to be the evolutionary origin for many of the coronaviruses. These rodents are warm blooded, like humans. Therefore, they provide optimal ecological conditions for zoonotic virus survival. However, there are at least 1,250 bat extant species on the planet, so it is possible that bats just act as a relevant reservoir for disease due to their huge species richness.
Could there be a man-made origin of SARS-CoV-2?
Dr Drexler discussed a few aspects of the conspiracy theory relating to a man-made origin of COVID-19: “The phylogenetic evidence to suggest that the origin of SARS-CoV-2 is in bats is very convincing – probably as good as we could ever get for a human pathogen. If the infection was man-made, then it was not very well done.”
A study that compared SARS-CoV-2 with other coronaviruses evidenced that it more sensitive to human interference. Therefore, it is highly unlikely that the strain was engineered to be a deadly virus.
There has also been speculation about whether scientists could have engineered the furin cleavage site of SARS-CoV-2 – a structure that is key to the virus pathogenesis. However, again, this is highly unlikely because when SARS-CoV-2 was compared to other coronaviruses, the furin cleavage site was not unique.
In terms of SARS-CoV-2, overwhelming evidence suggests that the evolutionary origin was in Horseshoe bats (Rhinolophus). Some coronaviruses also have intermediary hosts. Dr Drexler explained: “In SARS-related coronaviruses, very early on we incriminated the pangolin. But there is no absolutely convincing phylogenetic evidence to suggest that SARS viruses in the pangolin provide answers for what became the human infection. We may never know”.
Before COVID-19, no pangolin or bat species were among animals for sale in the Wuhan wet markets. Instead, there were many carnivores. Several experimental transmissions studies showed that carnivores appear to be particularly susceptible to SARS-CoV-2. This suggests that a carnivore at the Wuhan wet market was likely to have acted as the intermediary host for COVID-19.
Dr Drexler explains the COVID-19 trajectory
Typically, viral mutation rates are one million times that of their hosts. Furthermore, coronaviruses are unique among viruses as they have a proof-reading enzyme called ‘nsp14’. Due to the extremely large genomes of coronaviruses, the nsp14 protein is necessary to prevent the virus from being rundown with disadvantageous mutations.
However, COVID-19 has a unique opportunity to advantageously adapt because of the 500,000 global transmissions of SARS-CoV-2 per day. Dr Drexler stated: “When looking at the variants of concern, intense transmission occurs in areas with hugely dense populations of poor people. Therefore, we are most likely looking at immune escape at population level”.
To conclude, Dr Drexler anticipated that, in 5-10 years from now, SARS-CoV-2 will look like a normal coronavirus: “With much of the planet immunised, COVID-19 will likely behave like any other ‘common cold’ coronavirus would.”
The Association for Molecular Pathology (AMP) aims to advance the clinical practice of molecular and genomic laboratory medicine through education and innovation – ultimately, to enable the highest quality health care. The AMP Europe Congress 2021, titled Clinical Genomics: Beyond Somatic Mutation, recently took place online, bringing together several experts in the molecular pathology field to present snippets of their cutting-edge research.
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