Thanks to rapid genome sequencing technology and the work of hundreds of dedicated virologists and wildlife biologists around the world, we now have a good idea where SARS-CoV-2, the virus causing the worldwide COVID-19 pandemic, came from. Sometime in the Fall or early Winter of 2019, a closely related bat coronavirus made the leap into a human. It may have gone through an intermediate host first, or maybe not. In either case, it managed to adapt well enough to replicate and spread to another human, a phenomenon called spillover. The rest is history.
While many researchers are working to answer the remaining questions about SARS-CoV-2’s origin story, others are studying an even more pressing issue: what happens next? A recent paper in PLOS Pathogens suggests that the future may hold an ironic twist.
The same promiscuity that allowed this bat virus to make the leap into humans has already been shown to support its movement into domesticated and semi-domesticated animals. This isn’t the first time a coronavirus has demonstrated this ability. One of the established “common cold” coronaviruses, OC43, can hop between humans and cattle.
In principle, we might eventually be able to control the virus even if it gets into our pets and livestock, but what if it also spreads into wild animals? What if we give it back to the bats, for example?
As Olival et al. show, that’s a real possibility. The researchers first looked at historic examples of introduced diseases spreading into and among North American bats, then searched the literature for evidence about coronaviruses in particular. To date, nobody has found any beta-coronaviruses, the viral group that includes SARS-CoV-2, in temperate-zone North American bats. That suggests they would have no prior immunity to this virus.
Mapping the migration routes and looking at habitats and biology of these animals, the authors conclude that many species of North American bats could be exposed to SARS-CoV-2, and would be susceptible to it. Given how poorly the US has managed its response to the pandemic, there’s no shortage of virus circulating among humans on this continent, so it may only be a matter of time before the bats start catching it from us.
While the “spillback” of the pandemic virus into wild bats may not happen anytime soon, it could have far-reaching impacts if it does. For example, many North American bat species, already decimated by white nose syndrome, are teetering on the brink of extinction. They may not be able to tolerate another introduced pathogen, and losing these bats could destabilize entire ecosystems. At the same time, a bat reservoir of SARS-CoV-2 could provide an ongoing source of new spillover events back into humans, complicating control of the virus. To address that, Olival et al. advocate stepping up efforts to track bat diseases.
The paper is a literature review. Other than a detailed visualization of bat migration routes, the authors don’t present any new data. One reason is that studies such as the ones they propose, monitoring infectious agents in wild bats, haven’t been well-funded in the past. Indeed, one of the leading global efforts to look at circulating bat viruses had its funding cut in April for no good reason. Now the bats aren’t the only ones flying blind.