Why Do Bats Not Get Sick?

Bats Immune System

A newly published paper suggests that this virus’s source was bats, like SARS. Scientists sequenced its genome and compared it to other coronaviruses living inside horseshoe bats in 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 Ebola, Hendra, Marburg, Nipah, MERS, and Coronavirus. However, bats have widely misunderstood creatures with their somewhat ghoulish appearance and creepy associations.

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. Also, they passed 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. If specific bat components are somewhat human-like, that ability to virus across is much easier. A virus-like living in a bat may also be like living in us.

Why don’t bats 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 much 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, which has impacted their 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.

Here are a few reasons why bats, as a group, have a relatively high resistance to certain diseases:

Flight and High Metabolic Rate: Bats have a high metabolic rate due to their ability to fly. This high metabolic rate allows them to maintain a higher body temperature, which can inhibit the growth and replication of some pathogens. Additionally, the increased energy expenditure during flight may enhance immune system function.

Robust Immune System: Bats possess a diverse and highly adaptive immune system that helps them respond effectively to various pathogens. Their unique antiviral immune response allows them to tolerate viral infections without experiencing severe symptoms. Bats also exhibit a rapid immune response, enabling them to control and clear infections more efficiently.

Longevity and Slow Aging: Bats are known for their exceptional longevity relative to their body size. They have a slower aging process than other mammals, which may be linked to their ability to maintain a healthy immune system for extended periods. This prolonged immune competence helps them fight off infections and reduce the impact of age-related immune decline.

Coevolution with Viruses: Bats have coexisted with various viruses for millions of years, leading to coevolutionary dynamics. This long-term association has likely influenced the bats’ immune system, enabling them to tolerate viruses without developing severe disease symptoms. Some researchers suggest that bats’ immune systems have evolved to balance controlling viral infections and minimizing inflammatory responses.

Batwings are incredible, and not only because of the varying sizes. The bone structure of bat wings is incredibly flexible. They have four elongated digits that can flex and 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. That might mean certain death for some animals, but not for bats. Researchers seem to think these stressors built the bat’s superpower immune system. A bat’s immune system responds differently from humans 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 suggests 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, negatively impacting their health.

So to prevent these bats, they have evolved mechanisms to lessen their immune response, resulting in them 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 world members, 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. That allows mammalian cells to trigger an inflammatory response when detecting a virus. So essentially, by flying, bats constantly battle 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 through damaged 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. Most mammals have similar interferon proteins that kick in at varying degrees when they detect infection. But studies show that most bats have activated interferon-alpha genes, 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 coexistence with bat immune systems. It means they can become stronger and more resistant, 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 put 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 use bats to pollinate or spread seeds.

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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).

Julia Rose

My name is Julia Rose. I'm a registered clinical therapist, researcher, and coach. I'm the author of this blog. There are also two authors: Dr. Monica Ciagne, a registered psychologist and motivational coach, and Douglas Jones, a university lecturer & science researcher.I would love to hear your opinion, question, suggestions, please let me know. We will try to help you.

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