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  • If this bat were a human, she'd be in deep trouble.

  • She's infected with several deadly viruses, including ones that cause rabies, SARS, and Ebola.

  • But while her diagnosis would be lethal for other mammals, this winged wonder is totally unfazed.

  • In fact, she may even spend the next 30 years living as if this were totally normalbecause for bats, it is.

  • So what's protecting her from these dangerous infections?

  • To answer this question, we first need to understand the relationship between viruses and their hosts.

  • Every virus has evolved to infect specific species within a class of creatures.

  • This is why humans are unlikely to be infected by plant viruses, and why bees don't catch the flu.

  • However, viruses do sometimes jump across closely related species.

  • And because the new host has no established immune defenses, the unknown virus presents a potentially lethal challenge.

  • This is actually bad news for the virus as well.

  • Their ideal host provides a steady stream of resources and comes into contact with new parties to infecttwo criteria that are best met by living hosts.

  • All this to say that successful viruses don't typically evolve adaptations that kill their hostsincluding the viruses that have infected our flying friend.

  • The deadly effects of these viruses aren't caused by the pathogens directly, but rather, by their host's uncontrolled immune response.

  • Infections like Ebola or certain types of flu have evolved to strain the immune system of their mammalian host by sending it into overdrive.

  • The body sends hordes of white blood cells, antibodies and inflammatory molecules to kill the foreign invader.

  • But if the infection has progressed to high enough levels, an assault by the immune system can lead to serious tissue damage.

  • In particularly virulent cases, this damage can be lethal.

  • And even when it's not, the site is left vulnerable to secondary infection.

  • But unlike other mammals, bats have been in an evolutionary arms race with these viruses for millennia, and they've adapted to limit this kind of self-damage.

  • Their immune system has a very low inflammatory response; an adaptation likely developed alongside the other trait that sets them apart from other mammals: self-powered flight.

  • This energy-intensive process can raise a bat's body temperature to over 40ºC.

  • Such a high metabolic rate comes at a cost; flight produces waste molecules called Reactive Oxygen Species that damage and break off fragments of DNA.

  • In other mammals, this loose DNA would be attacked by the immune system as a foreign invader.

  • But if bats produce these molecules as often as researchers believe, they may have evolved a dampened immune response to their own damaged DNA.

  • In fact, certain genes associated with sensing broken DNA and deploying inflammatory molecules are absent from the bat genome.

  • The result is a controlled low-level inflammatory response that allows bats to coexist with the viruses in their systems.

  • Even more impressive, bats are able to host these viruses for decades without any negative health consequences.

  • According to a 2013 study, bats have evolved efficient repair genes o counteract the frequent DNA damage they sustain.

  • These repair genes may also contribute to their long lives.

  • Animal chromosomes end with a DNA sequence called a telomere.

  • These sequences shorten over time in a process that many believe contributes to cell aging.

  • But bat telomeres shorten much more slowly than their mammalian cousinsgranting them lifespans as long as 41 years.

  • Of course, bats aren't totally invincible to disease, whether caused by bacteria, unfamiliar viruses, or even fungi.

  • Bat populations have been ravaged by a fungal infection called white-nose syndrome, which can fatally disrupt hibernation and deteriorate wing tissue.

  • These conditions prevent bats from performing critical roles in their ecosystems, like helping with pollination and seed dispersal, and consuming pests and insects.

  • To protect these animals from harm, and ourselves from infection, humans need to stop encroaching on bat habitats and ecosystems.

  • Hopefully, preserving these populations will allow scientists to better understand bats' unique antiviral defense systems.

  • And maybe one day, this research will help our own viral immunity take flight.

  • From plant pollination to pest control, bats are an essential part of our ecosystems.

  • So why are they known as nature's villains? Find out more about these misunderstood animals with this video.

If this bat were a human, she'd be in deep trouble.

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B2 TED-Ed bat immune dna inflammatory immune system

Why bats don't get sick - Arinjay Banerjee

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    林宜悉 posted on 2021/10/24
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