This a creature we are pretty familiar with. Featuring in cult legends and horror stories across several cultures, including the hugely popular Vampire folklores of Eastern Europe, this is none other than the bat, a harmless creature perhaps widely misunderstood. But is it really that harmless?
(Bats have been found to host about 137 different types of viruses, about 61 of which can be transferred to humans)
As if by a peculiar whim of nature, bats have been found to host a huge number of zoonotic viruses (viruses having the potential to infect humans or other animals from their primary host). In fact, bats are host to the most number of zoonotic viruses per species (1.8, compared to 1.48 in rodents) and have been found to carry upto 61 species of zoonotic viruses.
The fact that most of the deadliest viruses to plague humanity in recent years (be it Ebola, Zika, Nipah, SARS or the one which is wreaking havoc across the world currently, the SARS COV 2) had their origin in bats is indicative of the safe habitat these viruses have in a bat’s body. In fact, as its well known now, researchers are suspecting that the very first infections of Covid-19 occurred in a seafood market of Wuhan, China, where bats, pangolins and other wild animals were being sold and butchered for consumption. From bats, the virus may have jumped into humans, possibly taking a detour through another intermediate host, like pangolin.
If you’ve read till now, perhaps you’ve been thinking this, But what makes the bat so favourite habitat for these deadly viruses, and why do they don’t get sick with those viruses? The second part of the question has finally been answered by Peng Zhou and colleagues in a paper published in the journal Cell Host & Microbe. Zhou and scientists at the Wuhan Institute of Virology in China found that in bats, an antiviral immune pathway called the STING-interferon pathway is dampened, and bats can maintain just enough defenses against illness without triggering the immune systems from going into overdrive. In humans and other mammals, an immune-based over-response to one of these and other pathogenic viruses can trigger severe illness.
Now, the answer to the first part lies in the uniqueness of bats. Being the only mammals capable of flying, it takes a lot of energy to accomplish this feat, which increases their body temperature to about 40 degrees Celsius. This means only those viruses capable of tolerating such temperatures can live inside their body. Unfortunately for us humans, this also means these viruses can easily tolerate elevated temperatures during human fever response.
Another effect of this unique flying ability is that this generates lots of harmful chemicals (reactive radicals) in the bat’s body. To overcome these and protect their DNA from damage, bats possess sophisticated defense mechanism. This poses a unique challenge to those viruses living in their bodies which have to bypass those defenses and ramp up their replication, as shown in studies conducted by Cara Brook et al, University of California.
“When you have a higher immune response, you get these cells that are protected from infection, so the virus can actually ramp up its replication rate without causing damage to its host. But when it spills over into something like a human, we don’t have those same sorts of antiviral mechanism, and we could experience a lot of pathology.”, says Brook.
A big brown bat collected by researchers in a cave near Ely, Nev. Big brown bats can live nearly 20 years in the wild. Credit…New York Times
But does this mean bats are the new nemesis of humanity? Not at all. It’s more of us humans encroaching into their territories than they on us which is causing this viral spillover. Besides that, they’re incredibly important pollinators, and also eat mosquitoes, which cause far more diseases in humans directly or indirectly. In conclusion, hating on bats or killing such beautiful creatures won’t help. We should instead focus on diverting resources in studying these animals and their unwelcome hitchhikers so that next time such a pandemic hits, humanity would be prepared. Date: June 25, 2020
Author: Ditam Chakraborty