By the ninth installment in this series we’ve moved away from our familiar domestic animals, but there are still a few species worth highlighting.
Bats aren’t actually one species though, they’re a diverse group of over 1400 unique species. Some eat insects, some eat fruit, some eat small critters like frogs, and some eat blood (yes, vampire bats do exist, but no, they don’t die if they’re exposed to garlic or sunlight). One thing they have in common is they are all flying mammals that live in large groups.
Bats are obviously a concern when it comes to SARS-CoV-2 because this virus (as well as its close relatives, the original SARS virus and the MERS virus) likely originated in bats. Bats can be little coronavirus factories, but remember that there are huge differences between bat species. We shouldn’t talk about “bats” as the source of SARS-CoV-2, because we’re really talking about one particular species, Chinese horseshoe bats (Rhinolophus sinicus), as the likely source.
Just because a virus can infect one species of bat, it doesn’t mean it can infect them all. That’s important because bats are incredibly widespread internationally, and often travel long distances (and obviously aren’t stopped by international borders). We don’t want SARS-CoV-2 to spread to other bat populations. The more we can keep this a human disease, the better, since it’s easier to control a pathogen in one species versus many (especially when some of them can fly). That’s one reason field research involving bats has been curtailed or suspended in many areas during the pandemic. We don’t want people getting near bats, as more person-to-bat contact increases the risk of exposing the bats to, and potentially infecting them with, SARS-CoV-2. The odds of such transmission are pretty low to start, given the small number of people who do that type of work and their limited direct contact with bats; however, it’s a small risk with potentially very big implications, so curtailing field research for now is logical.
We also don’t know the potential range of bat species that might be susceptible to SARS-CoV-2. Predictive studies based on ACE2 receptors suggest that most bat species are probably not susceptible. However, many still might be susceptible. We have to be very careful with these types of studies, as they’re useful but far from definitive. As you can see from the figure below from one ACE2 receptor study, it actually predicted horseshoe bats aren’t susceptible to SARS-CoV-2, despite the fact they are a leading candidate for being the initial source of the virus.Experimental studies are one way to sort this out, but they aren’t common because they’re expensive and difficult to do with bats (let alone when you toss a dangerous virus into the mix).
One experimental study from earlier this year looked at susceptibility of Egyptian fruit bats (Rousettus aegypticus) and found that 7/9 bats exposed to SARS-CoV-2 developed a transient infection. One of three bats that were placed in contact with those bats also became infected. That’s a bit concerning, since this species can be found in parts of Africa, Asia and around the Mediterranean.
Research involving other common bat species is lacking. So, prudence would dictate that we treat all bats as potentially susceptible until we know they are not. There are a number of other reasons to avoid direct contact with bats as well (rabies being a big one), but keeping bats away from people and people away from bat habitats is particularly wise now.
To finish off… yes, bats can carry lots of potentially harmful viruses. But, they also do a lot of good things ecologically, like eating tonnes of mosquitoes (which are important disease vectors too). Don’t blame this all on bats. We (people) are the ones who got it from the bats and then spread it all over the world.
Image: Horseshoe bat (source: http://www.bio.bris.ac.uk/research/bats/China%20bats/rhinolophussinicus.htm)