It’s been several years since scientists suspected the original strain of COVID-19 made the jump from bats to humans, and in that time, the virus has mutated and transformed into numerous variants.
But has it changed so much that the bats scientists believe may have served as COVID-19’s original incubator are now immune to its effects?
According to a new study published in the peer-reviewed journal Royal Society Open Science this month, the answer is no — bats are still at risk of catching COVID-19 from us.
And the possibility of transmission across many other species is still a very real, researchers say.
The study found that bats haven’t evolved defences against COVID-19, and are capable of being infected through largely the same process as humans: the spike proteins on SARS-CoV-2 (the virus that causes COVID-19) binding to specific receptors to enter host cells.
“We were hoping to see really cool adaptive evolution happening as the virus got more used to humans and less used to bats, but we actually saw that there wasn’t a whole lot of change,” Gregory Babbitt, an associate professor with the Rochester Institute of Technology and one of the authors of the study, said in a press release.
“Because this binding site has not evolved very much, there’s really not much stopping it from transmitting from humans to bats. If you look at the phylogenetic relationships of bats to humans, we’re pretty far apart on the mammalian tree. So it suggests that there would be pretty widespread cross-species infectivity, and the literature has shown there’s been a lot of evidence of that.”
In humans, the SARS-CoV-2 spike protein attaches to a receptor known as ACE2 – the very same receptor that exists in many bats of the genus Rhinolophus, also known as horseshoe bats – on the surface of cells.
However, evolving variants have developed mutations, many within the spike protein, which better allow them to evade vaccine-based immunity in humans, as well as immunity built up from previous cases.
In order to see if any of these newer variants were no longer able to infect bats, researchers ran all current variants of concern (VOC) against computer modelling of the binding receptors in these bats. These included the original strain of COVID-19, Alpha, Beta and Delta, as well as Omicron variants BA.1, BA.2 and BA.4/BA.5, among others.
“It would be dangerous to do experiments where we reinfected bats with human viral strains, so our computer-based simulations offered a much safer alternative,” Babbitt said.
Although the study found that bats could still be infected with the virus, there were differences in the way the different variants approached the body.
Researchers found that all of the VOC were better at binding to a specific type of ACE2 receptor called hACE2, compared to bACE2, while the original strain of the virus saw no difference between which of these receptors it was capable of targeting.
Omicron variants have more mutations within their spike proteins, which affected how they attached to the receptors.
The leading theory for where SARS-CoV-2 comes from is that it jumped to humans from bats, which have served as the animal intermediary for other viruses in the past.
Although the vast majority of the transmission of COVID-19 has been human-to-human transmission, we’ve seen other animals catch the virus from humans as well during the course of the pandemic, including gorillas, tigers, minks and housecats.
It may seem irrelevant to worry about bats being able to catch new strains of COVID-19 when humans are still dealing with its ravages in our communities, but understanding the potential cross-species transmission that a virus is capable of is part of trying to battle it, researchers say.
“As a result of the virus being able to infect multiple species and also being able to jump hosts, there are concerns that the introduction and circulation of new virus strains in humans could result in modifications of transmissibility or virulence and decreased treatment and vaccine efficacy,” the study stated.
“These findings provide evidence that recent human SARS-CoV-2 variants may re-infect bats and that the extensive species diversity of bats may also have profound effects on SARS-CoV-2 evolution in the future.”
The researchers added that bats are not that genetically different from us, no different than between most pets and livestock, and that bats and other mammals “could readily become host reservoirs that further promote the evolution of persistent cross-species infectivty as well.”
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