Coronaviruses likely to cross species boundaries again, experts warn

There have been three significant coronavirus emergences in 17 years — Expert Advisory Group Chair

Members of the Oireachtas Special Covid-19 Response Committee were urged to look to the future so Ireland can learn lessons and be better prepared when the next pandemic occurs.

In his opening statement at this morning’s meeting, Dr Cillian De Gascun, Director of the National Virus Reference Laboratory , urged the Committee to keep an eye to the future so Ireland might be better prepared across all sections of society and the health service, when the next pandemic occurred.

The occurrence of a third significant coronavirus emergence in 17 years meant that these viruses were likely to cross species boundaries again, he told TDs.

He told TDs the likely source of SARS-CoV-2, the virus that causes Covid-19, was believed to be bats.

Following surveillance carried out after the SARS pandemic of 2003, “we know that there were hundreds of coronaviruses circulating in bats”.

While bats were regarded as the most likely natural host for the virus, Dr Gascun told this morning’s meeting of the Committee, the recombinogenic nature of coronaviruses meant it could be difficult to identify the ultimate source, as different parts of the genome would have different origins.

The precise origin of the virus itself was unknown but SARS-CoV-2 was the seventh coronavirus known to infect humans, and a member of the Sarbecovirus subgenus of the Coronaviridae family.

SARS-CoV-2 was a novel virus and there remained much that was simply not known.

This contrasted with influenza viruses, for example, which reassorted, but did not typically undergo homologous recombination within RNA segments.

In addition, Dr Gascun, who is also Chair of the National Public Health Emergency Team Advisory Group, told Committee members that the most closely related virus to SARS-CoV-2 to date had been a coronavirus identified in a Rhinolophus affinis bat sampled in the Yunnan province of China in 2013.

The interesting thing about the 2013 virus was that despite being approximately 96 per cent identical to SARS-CoV-2, the part of the genome that encoded for the protein that would allow the virus to infect humans efficiently to human cells, was actually quite different.

It was this receptor-binding domain (RBD) part of SARS-CoV-2 genome that was, in fact, more similar to coronaviruses that have been identified in Malayan pangolins, which initially had led to speculation that a pangolin could have been an intermediate host for SARS-CoV2.

However, analysis of the available sequence data suggested that the most likely divergence date of SARS-CoV-2 from its most closely related bat coronavirus ranged from 1948-1982.

This would indicate that the SARS-CoV-2 lineage had not been a recent recombinant and that, despite intensified characterisation of Sarbecoviruses since SARS, viruses closely related to SARS-CoV-2 had been circulating unnoticed in horseshoe bats for many decades.

At this morning’s session, Dr De Gascun also expressed his deepest condolences to all of those who had lost friends and family during this pandemic.

valerie.ryan@imt.ie

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