A newly published paper strongly suggests, like SARS, the source of this virus was bats. Scientists sequenced its genome then compared it to other coronaviruses living inside horseshoe bats from eastern China. They found a close match. Slightly different from SARS but in the same family. Most of it will come back to bats. Also, bats are super hosts thought to be the sources of the Ebola virus, Hendra virus, Marburg virus, Nipah virus, MERS, and even Coronavirus. However, with their somewhat ghoulish appearance and creepy associations, bats have widely misunderstood creatures.
Professor Scott Weese studies and treats infectious diseases in animals. He says bats live all over the world. They’re essential in pollinating fruit and eating insects. And they’ve been passing diseases to one another in their vast colonies for thousands of years. But Weese says they also have an essential trait in common with us. Bats are mammals, so they are related to us. And if specific components of that bat are somewhat human-like, it makes that ability to virus across a lot easier. Meaning a virus that likes living in a bat may also like living in us.
Why bats don’t get sick or ill?
Why are bats linked to so many deadly viruses? The short answer is well because they can fly. Flying, especially for mammals, requires a lot of energy, with some smaller bats capable of beating their wings up to 17 times a second. This exerts a lot of stress on the bat right down to the molecular level.
The question is, why don’t the viruses sicken or kill the bats? They’re the only truly flying mammal, and that’s got to have some impact on its physiology. Peter Daszak studied bats in China for 15 years. He speculates that as bats evolved to fly somehow, their immune systems changed. The chemicals that bats use within the body to regulate viruses. Maybe some of those could be used as potential drugs against some of those viruses. Flying also gave bats the ability to spread disease quickly. Their bites, urine, and feces can infect people and animals on farms and in the wild.
Batwings are incredible, and not just because of the varying sizes. The bone structure of bat wings is incredibly flexible. They have four elongated digits that can flex, bend and a thumb that remains separate with a claw. Connecting these limbs in the digits is a skin membrane called the potassium consisting of two layers of epidermis and dermis surrounding blood vessels, nerves, and tendons. This membrane is key to how bats perfect their maneuvering skills in flight.
According to the zoological society of London, the ability to fly may protect bats from becoming sick. A bat’s heartbeat can surge to over 1000 beats per minute during the flight, and its body temperature can rise to more than 39 degrees celsius. That’s over 102 degrees Fahrenheit. For some animals, that might mean certain death, but not for bats. Researchers seem to think these stressors are what built the bat’s superpower immune system. A bat’s immune system responds differently from a human to these infections, preventing the animal from falling sick.
- Since most bacteria thrive best at 98.6 degrees Fahrenheit or average body temperature, fevers heat the body to kill the infection. It is because bats have a nearly constant fever. They’re immune to the diseases they carry.
Research suggested that flight may be the reason. It’s believed that when bats evolved to fly, their energy metabolism was altered to adapt to the high energetic demands of flight. But this increased metabolic rate can eventually damage their DNA which can negatively impact their health. So to prevent these bats, they have evolved mechanisms to lessen their immune response resulting in bats not being affected by these diseases. It makes them natural disease reservoirs, and because of this, they get a bad reputation. But they’re crucial members of the world, and those little creatures need help more than ever.
- The DNA damage triggers an immune response called white blood cells to kill off any potential pathogen invasions.
However, the natural consequence of this is inflammation, and given that bats undergo this process pretty much any time they take flight. But they don’t, and that’s because they’ve evolved to dampen the activity of sting proteins which are proteins. That allows mammalian cells to trigger an inflammatory response when a virus is detected. So essentially, just by flying, bats are on a constant battle of enduring stress while their immune systems fight off inflammation. It means they are left vulnerable to actual viruses and pathogens.
- When bat immune systems are triggered, whether, through damage DNA sustained flight or actual viral infection, their cells produce a protein called Interferon-alpha.
This protein essentially walls off virus pathogens and prevents them from replicating. Now most mammals have similar interferon proteins that kick in at varying degrees when they detect infection. But studies show that most bats have their interferon-alpha genes activated all the time, effectively containing viruses. So they remain dormant within the bat.
In fact, on average most bats have about two zoonotic viruses floating around their systems at any given time, making them the most potent viral incubators in the mammal kingdom. Bats live in large roots, with hundreds, even thousands in close quarters, and fly great distances. Their viruses can spread between them and linger in colonies for long periods.
Meanwhile, surviving virus pathogens adapt to living in coexistence with bat immune systems. It means they can become stronger and more resistant, significantly as bat body temperatures easily exceed 40 degrees Celsius in standard flight. So when their natural habitats are encroached upon, they’re forced into contact with other mammals, such as in wet markets where illegal wildlife trading sometimes occurs. The ensuing stress dampens bat immune systems, and they end up releasing more fluids: urine, defecation, sweat, and saliva. It can infect other animals directly or through intermediaries such as pigs, civet cats, pangolins, and even humans.
Environmental threats like deforestation and wildlife trade are putting bat populations under enormous pressure. In turn, this puts them in danger. We continue to infringe on their world by destroying their habitat, creating more opportunities for diseases to jump from one species to another. Like most of our natural world, we need bats. They play essential roles in ecosystems. From pest controllers to pollinators, thousands of plants rely on bats for pollination or to spread seeds.
Teeling, E. C. et al. Bat biology, genomes, and the Bat1K project: to generate chromosome-level genomes for all living bat species.
Letko, M., Seifert, S. N., Olival, K. J., Plowright, R. K. & Munster, V. J. Bat-borne virus diversity, spillover, and emergence.
Irving, A. T., Ahn, M., Goh, G., Anderson, D. E. & Wang, L.-F. Lessons from the host defences of bats, a unique viral reservoir. Nature 589, 363–370 (2021).