Bats, those mysterious creatures of the night, often find themselves in the media spotlight, but not for the reasons they truly deserve. Beyond the associations with deadly diseases like Ebola, COVID-19, and the recent Nipah virus outbreaks, bats are remarkable creatures with a lot more to offer than meets the eye.
The Fascinating Physiology of Bats
Flight and Resilience
Flying requires an incredible amount of energy. A bat in flight elevates its basal metabolic rate up to 15x. And to put that in context, a human at full speed running is only doubling their metabolic rate. And a rodent, perhaps, elevating it sevenfold. So this is more than twice the energetic expenditure... of any form of terrestrial locomotion. Their heart rates can skyrocket to over a thousand beats per minute. That's around 4 or 5 times more than their resting heart rate. But there's even more. It's honestly remarkable that when a bat takes flight it doesn't just drop dead.
So a bat in flight will elevate its body temperature up to 44 degrees centigrade. And 45 degrees centigrade is kind of the lethal limit of what mammals can tolerate. And that holds for bats as well. So when in flight they're pushing the sort of physiological limits... of thermal tolerance. And while all of this is fascinating.
you're probably wondering... what does this have to do with viruses? Well, stick with me because we are getting there.
So flight is essentially a huge stressor that resembles aging... and because it's a part of bats’ innate physiology they’ve evolved unique molecular pathways to mitigate that damage at the site of production. So essentially, bat physiology is resilient to the process of aging. You see, despite burning a ton of energy all of the time bats are shockingly long-lived.
Usually, there are trade-offs between metabolic output and lifespan and rodents are a great example of that. Typically, they only live up to a couple of years. Bats, however, are about the same size and have metabolic expenditure that exceeds that of rodents. But they're extremely long-lived. The oldest known that lives up to 40 years in the wild. So after correcting for body size bats are the longest-lived mammals on Earth.
So these special pathways that they've developed to mitigate the intense effects of flying have likely made them extremely tolerant to viruses... or at least primed them to successfully fight them off.
What happens when a virus enters the human body and in bats
When a virus enters a human, two things happen. Okay, more than two things happened. But let's focus on two, because who has the time?
Think of these like two switches that need to be turned on when a virus infects a cell... and off when the body is clear of the virus.
But there's a catch. Once that immune response switches on our bodies can sometimes start to experience some pretty severe symptoms... like a fever, body aches, and essentially inflammation... which, sure, fights the virus but also... The immune response causes widespread inflammation in the body which is and of itself highly fatal. But bats can't have their body triggering inflammation every time they experience an extreme stressor... because their entire existence as a flying mammal is an extreme stressor.
And so their switch responses to an invader work a bit differently than ours. And so their switch responses to an invader work a bit differently than ours. So in some species, their alarm switch is perpetually on. In other species, it's entirely in overdrive... which means they're sounding an alarm and releasing molecules to stop a virus from replicating before it even enters their body.
And their switch that triggers inflammation kind of has a permanent dimmer. So they don't feel these strong side effects. Bats are particularly adept at reducing viral loads to very low levels and simply tolerating whatever is remaining. Which might be part of the reason why the viruses they host are so much more dangerous to humans.
The longer a virus stays in a host, the more chances it has to replicate, mutate, jump to a new bat or animal, and ultimately become something more deadly.
Learning from Bats for Human Health
But before you start thinking about bats as these horrible, disease-ridden flying creeps... it's worth noting there is a lot we can learn from them... including how to better treat disease in humans.
So it's anti-inflammatory. And so we turn the alarm on and we dim the other switch. Of course, bats aren't invincible.
And recent studies have shown that bats under extreme stress... caused by things like rising global temperatures habitat loss and human interference... are more likely to shed and spread viruses. So I feel strongly that there is a win-win argument for bat conservation and human public health... because a healthy bat is simply less of a zoonotic threat to humans than a sick bat. While that does pose a zoonotic risk they also offer a really valuable... research source for new approaches in medicine.
Thanks for reading. And there is just so much I did not get to cover in this. Including how a broad diversity of species of bats might also contribute to why diseases they carry are so deadly... or even just the things that do affect bats... like white-nose fungus. There's a long list of topics to explore and this piece is just meant to be a primer. But hopefully, it makes you want to learn more.
I've included a bunch of links below to help you get started.
FURTHER READING (a lot of it…)
A link to Cara Brook’s lab if you’d like to follow up on her research: https://brooklab.org/cara-brook
This piece is written as a primer to help people better understand how incredible these animals are and what we stand to lose if they’re gone. Here are a few links about bat conservation and white-nose syndrome:
https://www.nps.gov/articles/what-is-white-nose-syndrome.htm
For more about bats and finding the next pandemic (and why habitat destruction makes these outbreaks more likely):
https://www.gavi.org/vaccineswork/five-reasons-why-next-pandemic-could-come-bats
https://www.reuters.com/investigates/section/global-pandemic-bats-overview/
https://www.pbs.org/newshour/science/scientists-focus-on-bats-for-clues-to-prevent-next-pandemic
https://www.propublica.org/article/australia-bats-hendra-research-pandemic-prevention