SARS-CoV-2, the cause of covid-19, isn’t the only coronavirus in the world we should be keeping our eye on. Scientists appear to have just discovered a new branch of coronaviruses in Brazilian bats that could have the tools needed to spill over and infect humans.
A large team of researchers in Japan and Brazil identified the possible zoonotic threat in a preliminary study released last week. The viral relative appears to be genetically distinct from other coronaviruses yet shares a feature with SARS-CoV-2 that may allow its kind to infect human cells. The findings suggest there are plenty of native bat coronaviruses in the wild with the potential to cause new epidemics in humans.
“The high diversity of viruses in bats therefore positions them as a key taxonomic group for zoonotic disease surveillance,” the authors wrote in their paper, presented as a preprint on the website bioRxiv.
A key similarity
Even prior to the emergence of covid-19 more than five years ago, scientists had been worried about coronaviruses causing the next big pandemic. SARS-CoV-2, its earlier ancestor SARS-CoV, and MERS-CoV are coronaviruses that successfully became human pathogens over the past two decades; all three belong to the betacoronavirus genus.
According to the study researchers, however, almost everything we know about the diversity of this genus is based on data collected from Asia, Africa, and the Middle East, with little genetic sequencing of such viruses in the Americas.
To help remedy this gap in knowledge, the team analyzed gut tissue samples collected from 70 bats in three sites across Brazil between May and August 2019. They found the new virus in a Parnell’s mustached bat (Pteronotus parnellii) and completely sequenced its genome.
Based on their analysis, the virus—which they coined BRZ batCoV—is different enough genetically to represent a previously unknown subgenus of betacoronavirus. Until now, five subgenera had been identified.
But the virus also appears to have something important in common with SARS-CoV-2: a functional furin cleavage site (FCS) at the S1/S2 junction of its spike protein. In fact, the FCS in BRZ batCoV is only different by a single amino acid compared to the one in SARS-CoV-2.
How worried should we be?
The FCS in SARS-CoV-2 is one of the features that helps it to infect humans. So finding something very similar in this new virus is certainly troubling. The researchers also note that other bat betacoronaviruses are known to have an FCS in the same location, suggesting it’s relatively easy for this feature to pop up in these viruses.
Another concerning aspect is that since there’s so little surveillance of Brazil and other areas in the Americas, it’s more than possible that BRZ batCoV and similar viruses have been circulating under our noses for quite a while.
The new research hasn’t been published in a peer-reviewed journal yet, a vital part of vetting any new study. The researchers also point out that they haven’t directly examined the infectivity of BRZ batCoV, a caveat that limits how much we can know about its risk to humans.
“Hence, although the presence of an FCS is clearly significant, any discussion of the zoonotic potential of this virus should be limited,” they wrote.
That said, this sort of research should be seen as an early warning signal. While the origins of SARS-CoV-2 are still being debated—even if most virologists are in the natural camp—many human diseases do first start off as zoonotic germs that successfully jump from animals to people (case in point, the original SARS). Bats and the viruses they carry are a prime suspect for causing the next big pandemic, and it’s urgent that we better track what’s out there, the researchers say.
“Our study provides a broader understanding of the phylogenetic and functional diversity of bat coronaviruses as well as their zoonotic potential,” they wrote.
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