Bats: man’s new best friend or deadly foe?

In the Chinese zodiac, 2020 marked the Year of the Rat. However, the Bat beat the Rat in the public eye that year with the emergence of SARS-CoV-2, better known as the virus responsible for the COVID-19 pandemic.

This was not the first time that a previously unknown virus infecting humans had been associated with bats.  In fact, there have been five other such viruses discovered in the last few decades, in regions ranging from Australia, Malaysia and China, to Africa and the Middle East.

Bats’ ill-earned reputation as a major virus reservoir has prompted strong backlash from the public. A politician in Australia has even gone to the extreme of proposing to “bomb the bats” in order to control disease outbreaks. 

Before bats were discovered to be a key reservoir of zoonotic viruses in the mid-1990s, the general public mostly knew of them from popular culture in the form of Batman and vampire bats. They tend to be maligned in most cultures, except in Chinese culture, where the Chinese characters for ‘bats’ (蝠 ) and ‘fortune’ or ‘blessing’ (福) look and sound similar. 

Bats’ ability to asymptomatically harbour a large number of deadly viruses has promoted a new area of research into the species’ immune system. Although still in its infancy, bat immunology research has already attracted great interest not only from scientists, but also from funding bodies and industry. 

This has been triggered by the understanding that bats diverged from land mammals more than 60 million years ago and evolved a unique immune system to deal with the stress of flight – a feat that they alone, as mammals, have mastered. Depending on the specific species, a bat’s heart can beat up to 1,000 beats per minute and its body temperature can rise up to 42^oC during flight at night. These physiological conditions can last many hours while they fly. 

Inflammation evolution

To deal with such physiological stresses, bats have evolved an immune system with a more effective balance between immune defence and tolerance. On one hand, the expression of certain genes related to their immune defence functions are elevated to be battle-ready. On the other hand, they have evolved multiple mechanisms to ensure some tolerance and prevent over-activation of their immune responses.  

For example, bats have evolved a way to avoid over-inflammation, which is the root of many human diseases. We believe that this balanced immune defence tolerance is largely responsible for many bat-unique biological features, including an exceptionally long lifespan, lower cancer risk and the ability to harbour viruses (another form of stress) without suffering clinical diseases. 

I believe we need to invest more into bat research to achieve two beneficial outcomes. First, by studying the intricate virus-bat interaction, we can better understand the mechanism by which bats harbour viruses without triggering diseases. More importantly, we can gain insight into the conditions that cause virus levels to elevate in bats – conditions that can trigger those viruses to jump from bats to other animals (including humans) and cause an outbreak or pandemic.  Second, by studying bats’ ability to deal with various stresses and live long without suffering from cancer and other diseases, it may be possible to discover new pathways, molecules or drug targets that benefit human health in general, thus creating a new Bat Biotech industry. 

While it is clear that studying bats and viruses carry certain risks – just as studying viruses form human or other animal sources – it is worth pointing out that such a risk is on a very different scale compared to the risk of a natural spillover of viruses from wildlife to humans via animal trading or tourism.

It is equally important to stress that the recent emergence of bat-borne zoonotic viruses is not the fault of bats as they have coexisted with these viruses for millions of years without any problem. If any species is at fault, it is us, humans, as the range and impacts of our activities – from animal trading, urbanisation, global travel and global warming – have been the real driver of zoonotic virus spillovers into human populations.

To conclude, as a scientist who has studied bats for the last few decades, I believe they can be more of a friend than a foe and that increased bat research will benefit mankind in more than one way.

• Linfa Wang is a Professor with the Emerging Infectious Diseases Programme at Duke-NUS Medical School, Singapore. He played a leading role in identifying bats as the natural host of the Severe Acute Respiratory Syndrome (SARS) virus during the early 2000s.

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