world to pursue and achieve your own dreams. >> announcer: the following is a cnn special report. bats throughout human history seem to have this image as evil, dark and dangerous. they seem to have got this bad impression in our cultures. there's definitely something odd about them. but just because they're odd doesn't mean they're bad. bats are actually quite fascinating animals. the more you get to know them, the more fascinating they are. the more social creatures you see them become. and some of them are really beautiful. but bats do carry the viruses

they carry, and unfortunately, right now, it's very strange. we've probably got a bat virus that's killing people. ♪ good evening. i'm anderson cooper. when covid-19 first surfaced at the end of 2019, scientists around the world wanted to know where it came from and how this deadly virus ended up in humans. although answers are not certain, it seems likely the coronavirus originated in bats. bats are diverse and ancient creatures, and they've been on earth longer than we have. despite that, there is still a lot we don't know. tonight we take a look at this enigmatic animal and dig into the mystery of covid-19.

in the last 20 years, some of the deadliest virus outbreaks have come from bats. sars, marburg, ebola. so what is it about these creatures and the way they spread pathogens that can be so dangerous? >> the fact that bats are carrying viruses is not in and of itself extraordinary. every animal has its normal suite of viruses and bacteria that it normally carries. people do as well. we carry viruses, we carry bacteria, the majority of which are benign or beneficial, some of which cause disease. it's the fact that bats do tend to carry a higher proportion of viruses that have the ability to infect people. the question is really why we see some of these incredibly bad viruses coming out of bats? >> it was 7:00 p.m. on december

30th, 2019, when a package arrived at the wuhan institute of virology. in it, medical samples from a local infectious disease hospital. several patients were suffering from atypical pneumonia. doctors suspected a possible novel coronavirus. dr. shi zhengli's cell phone rang shortly after. >> she got a call from her boss who said, drop whatever you're doing and come back to the lab right now. >> dr. shi is known in china as the bat woman. she's one of the leading experts on bat-borne diseases. >> she's the director at the center for emerging diseases at the wuhan institute of virology. >> it as biological level 4 facility. biological safety 4 refusal research is the highest level of containment that exists for studying pat ining path conveni viruses.

>> doctors feared the cluster of atypical pneumonia patients in wuhan might be infected with the same family of viruses that caused the outbreak of sars acute respiratory syndrome. >> more and more people were getting infected. we started to see on chinese social media in particular, the concern was growing. >> in new york, ecohealth alliance, a nonprofit organization devoted to tracking emerging diseases, began to take notice. >> we started to get our first inkling that something unusual was happening by looking to social media in china. they mentioned there was an unusual cluster of respiratory disease going on. and i remember talking to peter daszak that this might be another sars-like event. >> peter daszak is the president of ecohealth alliance. he has worked closely with the wuhan institute of virology and dr. shi. their collaboration was crucial in discovering the origin of the 2003 sars outbreak. the world health organization assembled a team including daszak, shi, and wang,

considered one of the world's top emerging disease experts, to find the source of the deadly outbreak. these virus hunters were pursuing a theory that bats could be the origin of sars. the team headed to the hunan region of southern china to try to solve the mystery of sars. >> shi and other researchers started exploring caves in southern china, looking for bats that could have been the origin of that first sars outbreak. >> dr. john epstein was a researcher on that expedition. >> when we go into an environment like a bat cave to catch bats, we have to protect ourselves. that includes gloves, we wear a respirator, like a mask. and we'll wear eye protection. >> we're walking into caves that could carry the next pandemic. that's a risky thing. what we do is we go in during the day to scope out where the bats are and try and work out

what species are in there. then what we do is set up nets outside and catch bats as they fly out in the evening and go back in the morning. >> we do everything we can to ensure the safety and well-being of the animals and we have a basic set of samples we collect. oral swabs, fecal pellets, blood. and we take measurements. >> over the course of eight months, they sampled caves all over southern china and then they took all these samples back to the lab. >> it really took the better part of eight years of consistent and persistent sampling, testing, different horseshoe bat populations around until we finally found the missing link we were looking for. >> that link was a bat virus genetically connected to sars and capable of jumping directly from bats to humans. >> that was the nail in the coffin for us in terms of this coming from bats. >> dr. shi told us bat-borne coronaviruses will cause more outbreaks. we need to find them before they

find us. >> that original sars coronavirus in 2003 started in guandong province, china. spread to hong kong, taiwan, and then the rest of the world, causing 8,000 cases and 800 deaths. >> that same year, the chinese government approved construction of the level 4 lab, the first in china. it opened in 2015 and is rated to study the world's deadliest viruses. >> translator: this p-4 laboratory will mainly be used for research on highly pathgenic infectious diseases and for which there are currently no medicines or vaccines. >> flash forward to the end of 2019, that's when the team in wuhan began to investigate the strange new virus. the genetic sequence of the virus was mapped fairly quickly. dr. shi compared it to a database of 500 new coronaviruses previously identified by ecohealth alliance.

there was a match. its official name became sars cov 2. the virus that calls covid-19. called covid-19 because it emerged in 2019. the new coronavirus was 96.2% similar to a virus taken from a horseshoe bat in 2013. so what does that mean exactly? >> well, 96% is a different virus. so it's a bit like the difference between us and chimpanzees. a different species of virus. but what it tells us, where the virus probably came from. it means that sars covid 2 probably came from bats, and probably in southern china. >> wuhan is 1,000 miles away from the southern subtropical regions of hunan province, where dr. shi says the coronaviruses have the greatest risk of jumping from animals to humans. >> most of the coronaviruses shi had studied had been in southern china, and wuhan is in central china. when shi first found out there was a coronavirus outbreak in

wuhan, she did firmly wonder, is there some chance that it could have come from her lab? >> the wuhan institute of virology is just a few miles from where many of the first cases were reported. >> dr. shi was facing this mounting pressure. that's very alarming, particularly for those who work within that lab. >> shi and her colleagues immediately isolated the virus, sequenced it, tested its behavior, and she was very relieved when she discovered that it didn't come from their laboratory. this virus has never been seen anywhere in the world. >> as her team raced to find answers, the disease was spreading fast. >> when the chinese minister of health announced that community spread was rampant in wuhan, and that asymptomatic spread was occurring, that meant the disease was out of control. >> the chinese government said they traced the source of the new virus to the western edge of a seafood market in wuhan where wild animals were being sold and

slaughtered for food and medicine. >> i can't think of a better place to be a virus than a wet market. >> 16 years before the wuhan outbreak, animal traders at guangdong caught the original sars virus also in a wildlife market. >> the viruses take hold, they swap around, and then people come and breathe it in and get exposed to it. that's how viruses spill over. >> in wuhan, the initial cluster of 41 cases of severe pneumonia, about half those patients had been to that market or worked in that market or had some degree of contact with it. >> the chinese government shut down the market. and early on tried to keep information from spreading, communicating little about the early cases. >> not only was it shut down, it was also cordoned off. you had police at nearly every corner. >> months later, the chinese

centers for disease control and prevention announced that while the new virus was found in several locations in the wuhan market, all the animals they sampled tested negative. since then, other theories about the possible source of the virus have emerged. >> one of the theories that circulated was that this originated from a wildlife trapper. somebody that has brought in one of these wild creatures into the market for sale. >> the only information we have from the investigation of the market was that environmental samples were collected, and of about 580 samples collected, about 37 of them came back positive for sars cov-2, this virus. >> dr. epstein says the jury is still out on whether the wuhan market is ground zero for covid-19. but he agrees that wildlife markets are breeding grounds for the next bio disaster waiting to happen. >> why wouldn't china just shut

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scientists believe covid-19 may have had its roots in a community of horseshoe bats in southeastern china. these particular bats represent a very small subset of horseshoe bats all named for the shape of their noses. there are actually dozens of varieties of horseshoe bats living in a number places, including the temperate and tropical regions of central europe, africa and asia. in fact, there's incredible diversity among bat species. bats can be found living all around the world, on every continent except antarctica. however, the diversity and unique abilities of bats is also what makes them tough to contend with when it comes to disease. they're the only mammal capable of actually flying, so they can easily spread viruss to other animals and communities.

>> some migrate thousands of miles, and hence the viruses that they carry traffic along those migratory routes. >> and though some of the pathogens bats play host to can make them sick, like rabies, they also have the unique ability to host and withstand some viruses without getting sick. >> understanding how bats co-exist with diseases is very critical. bats have a very unique relationship with pathogens generally. they have a unique biology, and it allows them to coexist with pathogens in different ways. >> there are various theories about why that is. it might have to do with how long bats have been around. >> bats are ancient species. they have been on planet earth a long time, and that means they've had a long history of being exposed and adapting to viruses in nature. >> another theory involves their body temperatures. >> a lot of people have come up with these sort of armchair solutions.

like maybe it's because they fly, and when they fly their body temperature gets a little higher, so it's like a fever and that gives them the ability to handle more viruses than other kinds of animals would. >> dan riskin is an evolutionary biologist and tv host who did his ph.d. work on bats. >> when a virus gets into a human and a human responds by getting a fever which is effective against a lot of viruses, it doesn't work on the bat ones because they're used to these warm temperatures anyway. >> so if a virus is already used to a high temperature because of bats, that rising of the fever in the human may not be effective to kill off this virus? >> exactly. >> some bats have the ability to drop their body temperatures very low in the winter. so perhaps that also helps their unique immune systems. normally, the pathogens stay hidden in bats' bodies and they don't make the jump to humans. so how do humans get infected? that's what is known as zoonotic

spillover, when diseases cross from animals to people. sometimes that spillover occurs between an animal and a human, and then transmission going forward is human to human. that's called community spread. >> perhaps the best example of that would be hiv. the transmission happened from primates to humans many years ago, and now it transmits in human-to-human transmission. >> covid-19 is another example. but you can also have a disease that stays in a particular type of animal which then acts as a reservoir. in that case, humans are usually infected by an animal, not another person, like with rabies. >> sometimes viruses are carried by mosquitos. a mosquito might bite an animal that carries that virus and then bite a person and transmit it. they're like flying syringes. >> no matter how a disease makes the transition from wildlife to

humans, one thing is consistent. there has to be contact. >> oftentimes it's through indirect or accidental exposure. an animal that's infected may contaminate food or water people are eating and that's how they get exposed. >> with these big open markets, there's a lot of people, so there's a -- it's a very conductive environment for virus cross-species transmission events. >> it's an opportunity for animals that might have never have contact with each other in the wild, being artificially being brought into a highly dense, congested, and highly unhygienic situation. >> how do things spread from bats to either humans or other animals? just through droppings or -- >> it probably varies from any one case to another. >> typically, bats shed viruses the same way humans do. in saliva, urine and feces. if a bat is highly stressed and sick, does it shed more virus? >> yeah, absolutely. that's one of the issues with these wet markets.

for bats, they have coronaviruses that they've adapted to, and they're totally fine. but you put them in a wet market situation, they get sick, they get stressed. they succumb, just like if you've worked too hard and you suddenly come down with that flu, the bats get overworked. >> sometimes with zoonotic spillover, there can also be an intermediary animal. so bats transmit to another species, then that species transmits to humans. in the case of covid-19, as of now, no one can say for sure how it ended up in people. >> all the evidence we have suggests this was a virus that originated in bats and made its way into people through a natural process. >> but at this point, the greatest risk of getting covid-19 is from other humans, not bats. >> really, what matters is the way that we interact with bats. most epidemics are driven by human behavior. it doesn't matter that these viruses are happily existing in a wild animal in the middle of a forest. when people encroach on that

environment, we're creating opportunity for a bat virus to get into people. ♪ ♪ be it discovering talent in different continents... and entirely different sports, or discovering a smoother whisky by double-aging, sometimes, it's just better to stay curious. dewar's the only thing a disaster can't destroy is hope.

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they account for approximately 20% of all the world's mammal species. how many species of bats are there? >> 1,421 is the latest count, but we add at least 20 new species every year. >> so there are still species of bats that have never been -- >> oh, yeah. >> -- discovered? >> oh, yeah, absolutely.

>> nancy simmons is the curator in charge of mammalogy at the american museum of natural history. >> why are bats nocturnal? >> well, the thought is that actually, the ancestors of all mammals were probably nocturnal. small animals sort of scurrying around in the age of dinosaurs. it gave them access to resources that other animals like dinosaurs couldn't use. so bats basically never gave up that lifestyle. whereas the ancestors of us, primates, at some point gave up the nocturnal lifestyle to be diurnal. >> but working at night, it helps the bats how? >> if you think about what the animals are that are active in the air during the day, it's birds. and by being active at night, bats are not competing directly with birds. so the bats basically fulfill all the same ecological roles that birds do, only they do it

at night. >> bats are unique mammals. though structurally in some ways they're similar to humans. so bats have four limbs, two of them are attached to the wings. >> two of them are the wings. >> are the wings, okay. >> yes. they have all the same bones that humans do. in the upper arm, the forearm, there's two bones, wrist bones. then the bones that support the end of the wing are long finger and hand bones. >> bats' living and eating habits vary widely across the 1,421 species that exist. there's some that roost in trees, others under leaves, some in caves. some bats eat insects, others fruit, or even fish and frogs. these species, some of them are living right next to each other. >> oh, absolutely. one square mile of rain forest in, for instance, the brazilian

amazon, could have 100 species of bat. >> the smallest bat in the world, it's this tiny thing in thailand that weighs less than a penny. the biggest bat in the world has more than a six-foot wing span. there's a bat that lives in the cloud forests of ecuador that has the longest tongue of any mammal. this thing has a tongue that is 1 1/2 times the length of its body. if you stick your arm straight out in front of you and imagine your tongue could touch your fingers, it's three times that long, so it can get into a flower to pollinate. >> wait a minute. so relative to its body size, if i stick my arm out, if my tongue could go to the end of my arm this bat's tongue would go two more arms? >> that's right. >> there are a number of cute bats including one dubbed the panda bat.

and another, the tube-nosed bat, discovered in 2017 which made news for its resemblance to the former hairstyle of nsync's lance bass. >> there's the honduran white bat which looks like a cotton ball. you have your flying foxes that look like puppies but then you have some really ugly bats like wrinkle face bats. i like the ugly bats more than the cute bats. >> a bat that only a mother and dan riskin can love. >> blood-feeding bats, or vampire bats, do exist. but they're only about .2% of all bat species. they live in central and south america and prey on the blood of birds, pigs and cattle. >> vampire bats are super weird among bats. they sneak up on a cow. they put their face up against the cow. they've got heat sensors on their nose to tell where the blood is close to the skin. they shave the area with their teeth before they cut. they lick the area to clean it,

then they make a little divot with their front teeth, and they put their jaw up against that hole, and they lick and they drink and they bee. it's completely creepy. who else does that? >> i'll tell you who else. a serial killer does that. however, vampire bats don't kill their victims. they just act like a mammal-sized parasite. i've heard you say that the weirdness of bats was scientifically interesting to you. >> the faces of bats is a perfect example of that. if you take a bat that has a weird flap on its nose, you think that's a strange-looking adornment, it turns out a lot of bats have food in their mouths when they're trying to echolocate and it is hard to shout when you have food in your mouth. so they hum that echolocation. that weird flap actually points echolocation sound where they want it to go. >> most bats navigate and hunt for food in the dark using echolocation in which they emit

sound from their nose or mouth and then listen for the echo that bounces back to create a mind map of their surroundings. their often oversize ears also help. some species of bats have such sensitive hearing, they can detect the sound of an insect landing on a leaf. are bats social animals? >> it depends on the species. some bats spend their whole lives pretty much alone. other bats will mate for life. you have some species where there's a male and a harem of females, where he gets to mate with all of them. but they have their own likings in mind, so they'll sometimes cheat with nearby males from other colonies. there's like a whole soap opera going on with bats when it comes to mating. by the way, bat mothers are excellent mothers. imagine having a baby that weighed a quarter of what you weighed, and then the baby holds on to the mother's nipple with its teeth while she flies around. so i weigh about 200 pounds. the equivalent would be if i

took a 50-pound weight and put it on my nipple with a jumper cable and just went for a run. it's just incredible what these mothers do. >> wow. uh -- that's a visual that's going to be with me for a while, dan. ongest lasting aa battery... (music) energizer ultimate lithium backed by science. matched by no one. ♪ come on! ♪ over here! ♪

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in north america alone there are 46 different species of bats.

most of which are small insect-eating varieties like the big brown bat and the little brown bat. but in the southeastern parts of the united states, in particular in texas, there's an abundance of one species. the mexican free-tailed bat. the bracken cave outside san antonio is believed to be home to the single largest colony of bats in the world. >> every year during the spring and summer, i think there are something like 30 million bats in this cave in the summer. >> in the cave? >> in the cave in the summer. there are so many bats that the local weather stations use their doppler radar. they can see the cloud of bats coming out and spreading out over the landscape to catch insects. >> really? >> it takes hours for them, because there's so many of them commuting, basically, from wherever they're sleeping during the day to where their food is. >> and they go the same way each time, usually? >> yes. >> in an ecosystem, what role do bats have?

>> yes. they're really a critical, key component. for instance, insect-eating bats, because they consume so many insects, they play a large role in controlling insect populations. >> a normal-size bat can eat up to 500 to 1,000 mosquitos in an hour. mosquitos that might be carrying diseases like zika, dengue, or malaria. if you're in an area where there are a lot of mosquitoes and you see bats at night, you should be thankful for those bats. >> absolutely. >> and all that insect eating translates into big money saved for agriculture. the mexican free-tailed bat of texas, for example, eat huge numbers of moths, protecting the corn crops of the region. >> people have estimated the financial impact of bats on the u.s. economy is that they're worth well over $1 billion every single year. >> really? >> yes. in terms of how many pesticides we don't need to use. >> but pest control isn't the

only contribution to the ecosyst ecosystem. the droppings of fruit-eating bats, particularly in rain forests, help disperse seeds and regenerate trees and plants previously cut down. and that's not the only benefit. >> bat droppings are full of nitrogen so they're good for crops. and there are all kinds of stories about these caves in the united states being harvested for fertilizer, then for explosive for the civil war. >> there are also bats that serve as the only pollinators of particular types of bananas, mangos, and even cacti. the muzzles on these long-nose bats are designed to fit perfectly inside these cactus blossoms, blossoms that only open at night. >> agave which is used for tequila, that is pollinated by bats. >> exactly. who doesn't love tequila, right? just right there, that should be reason enough for people to love bats. >> despite the millions of bats in bracken cave, in north

america, over the last decade and a half, bat populations have been plummeting all because of an outbreak they've been fighting of a disease called white nose syndrome. >> it's a cold-loving fungus that grows on the bat when the bats are hibernating in the wintertime. and unfortunately, this has affected something on the order of a dozen different species of north american bats. in some cases, populations have declined over 90%. >> really? that's huge. >> it's huge, yes. it's a terrible threat to bats. and ironically, it's a disease that we brought to bats. the fungus that causes this disease is identical to fungus that naturally occurs in europe. the thought is it was simply brought over by people, it was accidentally introduced into bat caves. >> so while we're fighting a virus that potentially came to us from bats, bats are fighting a disease that potentially came to them from us. in fact, no north american bats are known to have covid-19.

among bat researchers, there is a concern that humans will give covid-19 to bats. >> emerging infectious diseases can go both ways. right? we do know that some other animals can get covid-19. for instance, the tigers at the bronx zoo. >> for now, most research involving handling of bats across the u.s. has been put on hold, because currently humans are potentially the bigger threat to bats. want to sell the best burger in every zip code?

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for many of us, when we think of bats, we think of one thing. rabies. the threat of that virus is often misunderstood. >> it's not very common for americans to get rabies. >> dylan george is a former white house adviser for biological threat defense. >> in any given year there's anywhere from zero to one to two people might get infected from rabies in bats or potentially from foxes or raccoons or skunks. >> rabies has actually been around for 2,000 years. for most of that time, if you got it, it was a death sentence. without treatment, it's 99.9% deadly.

one of the big problems in europe and the u.s. used to be wild rabid dogs. >> ancient medical experts developed a lot of odd ideas about how you would cure rabies. they used to believe that one way to stop rabies from killing you was to take a hair from the tail of the rabid dog and insert it into the bite wound, and this is the origin of the phrase "hair of the dog" which we talk about in the context of hangover treatment. >> then along came louis pasteur in the mid-19th century. he'd been working on a vaccine for years and eventually decided to try it out on a young boy who had been bitten by a rabid dog. the vaccine worked. >> most of the cases in the united states do come from bats. but the risk is low. so unless you see a bat behaving very strangely, moving around during the day in a funny way, more than likely, the bat won't be a risk to an individual.

>> okay. i'm coming. i'm coming. i'm coming, guys. >> joseph d'angeli spends a lot of time answering questions about rabies. because he spends every day around bats. >> there you go. oliver, oliver is more fascinated with you all. come on, are you going to take what you want? go ahead. they all have their favorites, of course. >> known as new jersey's batman, he became fascinated with bats as a young boy. >> my father was a nightclub and restaurant and bar owner. so i was destined to be nocturnal. and i used to very often accompany my father to work. every so often i'd go outside right before sundown, and i would see these animals flying around the street lights. and my father pointed them out to me and he said, those are bats. >> he quickly became obsessed he passed many childhood days in

the bronx zoo ogling these often feared and reviled creatures. >> the stigma attached to bats was horrible and i felt like the animal that i was seeing in person was not matching the description that people were giving me. around the world, bats are a sign of good luck, fertility, growth, everything you can think of. bats are usually the opposite of what they're considered here in america. >> as an adult, the batman became the showman as the lead singer of the '80s glam metal band rocks. >> it was a very different world. although it definitely paralleled the bat world. because we were pretty much active at night and sleeping during the day. >> then in the early '90s after attending a lecture on bats, he decided to change careers. >> i just started getting more and more into the idea of doing something for something else other than myself. the rock star thing is a little megalomaniacal.

but the bat thing was, these guys need help. >> he decided to leave the rock world behind and start working as an advocate for bats. >> so when a baby bat is born, he goes to the side and clings underneath the mama's wing. >> he became a licensed -- a person who studies bats, and opened up the wildlife conservation center in new jersey. >> this is claudia. claudia is usually pretty tolerant of being handled. each bat has a different personality, different behavior, sometimes even a different look to them. >> over the last 25 years as an educator, one of his goals has been to make people less afraid of bats. because of that, he purposefully chose to feature fruit bats, native to africa, asia and australia. they're commonly known as the flying foxes. >> they are more attractive and more appealing to people. they look like my little flying chihuahuas, i call them. they just really are much easier to use as educational subjects and to get people's fears reversed.

>> when the wing is around the face like that, they're using their wings as built-in blanket. >> he's part of a larger movement that's been taking place for the last three decades in the united states, teaching people why these creatures should be protected, not feared. >> we're all here for one purpose and for one target and one direction, and that's to help these animals and to help people understand why these animals need our assistance. they're so much like us. they are different looking, different colors, different sizes, different shapes, different importances, different jobs that they do. and i keep going back to, that is really what i think, at the end of the day, makes me love them so much that they are like people. when life gets back to normal, go outside and look up and go and find some bats. 're camping s 're camping s and you get the biggest spot, and you swam in the river all day in the warm afternoon sun... that's pure gold.

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every year, we, as a species, deeper and deeper into bat habitat and those of other wild creatures. exposing ourselves to new, and dangerous, viruses. with the dramatic increase in travel, a rise in global trade, we're now capable of spreading those viruses, far and wide. scientists warn that what we've

created is the perfect storm for a new pandemic. >> we are, without a doubt, going to see more epidemics, like covid-19, or perhaps worse, unless we really change the way that we're interacting with our environment. >> the first, major epidemic of the 21st century was sars, in 2003. other outbreaks, quickly, followed. 2009, it was h1n1 or swine flu. 2012, mers, middle east respiratory syndrome. then, the large, ebola outbreak in 2014. zika virus in 2015. and now, covid-19. >> they're increasing, in frequency. they're coming quicker, they're going to spread quicker, they are going to infect more people. and they're going to cause more economic damage, because we rely on that globalized economy, more and machi

and more each year. >> in a lab, researchers in berkeley, california, are looking for clues on how to help humans fight viruses like covid-19. >> there is actually a lot we can learn from bats. this group of animals that's been around for millions of years. how can we look at their history with viruses and take that knowledge, and think about therapeutics and treatments for ourselves? >> what is it about bats that allows some of them to host these viruses, without showing any illness? >> that's the question that cara brooke is trying to answer. brooke is a disease ecologist who began studying bats in madagascar, in 2012. she and her colleagues are investigating how the bats' immunity keeps them safe from harm. >> i have always been fascinated by bats, as host sources of infectious diseases that transmit to humans. in the case of certain bat

species, they appear to be perpetually primed to fight viral infection. >> reporter: scientists believe that, understanding a bat's immune system can help develop a human battle plan for fighting these diseases, on a global scale. >> it's an opportunity. what is it about the bats' metabolism, immunity, or physiology, that they've got that we could use? >> that might actually hold an answer for treating virus? >> if bats can handle thousands of different viruses at a much higher load than humans can, let's find out why and use that. >> brooke and her team infected the cells of two bat species with different viruses. then, they watched as the virus is spread and the bat cells mounted a strong defense. different than what would happen with humans. >> when a virus infects a cell, your immune response will recruit immune cells to the site to try and clear that infection.

>> and the signal to all sorts of cells that have not become infected. a virus is here. turn on your defense system. >> and typically, this manifests as inflammation. >> in humans, inflammation, oftentimes in the form of fever or swelling, helps fight infection. but too much, or inflammation that goes on for too long, can do more harm than good. it can even cause death. >> typically, more than half of the damage that results in disease tends to be the damage of the immune system attacking the host, itself. and we call that immunopathology. >> that's actually how the disease starts. >> but, bats' immune systems don't respond the same way as humans. >> it seems that bats are able to mount robust, immune responses, but not experience that inflammation. >> some bat species are actually missing the genes that we, and other mammals, have that trigger the inflammatory process.

>> the same adaptation, also, favor them to carry virus. >> it doesn't appear that they get sick, or very sick, when they are carrying viruses that can be deadly in other people and animals. >> so, could studying bat immunology help us, humans, create possible treatments to fight this current and future pandemics? what do you think is the greatest challenge in terms of finding a treatment or cure for these viruses? >> well, to my mind, the greatest challenge is the number of unknown viruses that are out there. i mean, we think there are about 1.7 million unknown viruses of the type that can get into people. and we got to get ready for these. find out what they are out there, get vaccines, not just the ones we know about, but the ones we are discovering right now. >> bats already contribute enormously to research that could, one day, be helpful to humans. they are being studied to see how they combat aging because

they tend to live longer than other mammals their size. research on bats is, also, helping the fight against cancer. scientists are trying to understand why bats don't develop tumors, like other mammals. and now, the possibility that they could help us fight current and future coronaviruses. >> people are working on vaccines. they're working on drugs. that's the -- that's what we're looking for. and i see it as an opportunity. >> many people are surprised by the physiological similarities between bats and humans and the information we may be able to extract from that. in addition to the anti-aging and cancer-research studies, scientists have also been looking into the saliva of vampire bats. it's got special, blood-thinning agents, which helps them syphon off their victim's blood. to see if there could be blood-thinning insights that could be helpful for humans. in the meantime, researchers agree it's our job to protect

these extraordinary creatures and their habitats because as we learned from the covid-19 pandemic, if we don't protect them, we're actually putting ourselves at risk. thanks for watching. good night. hello and welcome to our viewers in the united states and all around the world. i'm michael holmes. appreciate your company. coming up, here on cnn "newsroom." major developments on the christmas-day bombing in nashville. investigators focus on a new theory behind the cause of the explosion. with more americans dying from covid-19 this month than any other, president trump let the clock strike midnight on that relief package. and that means millions could now be without unemployment benefits. plus, the rush