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← What vaccinating vampire bats can teach us about pandemics

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Showing Revision 6 created 10/31/2019 by Oliver Friedman.

  1. The story that I'm going
    to tell you today,
  2. for me, began back in 2006.
  3. That was when I first heard
    about an outbreak of mysterious illness
  4. that was happening in the Amazon
    rainforest of Peru.
  5. The people that were getting sick
    from this illness,
  6. they had horrifying symptoms, nightmarish.
  7. They had unbelievable headaches,
  8. they couldn't eat or drink.
  9. Some of them were even hallucinating --
  10. confused and aggressive.
  11. The most tragic part of all
  12. was that many of the victims
    were children.
  13. And of all of those that got sick,
  14. none survived.
  15. It turned out that what was killing
    people was a virus,
  16. but it wasn't Ebola, it wasn't Zika,
  17. it wasn't even some new virus
    never before seen by science.
  18. These people were dying
    of an ancient killer,
  19. one that we've known about for centuries.
  20. They were dying of rabies.
  21. And what all of them had in common
    was that as they slept,
  22. they'd all been bitten by the only mammal
    that lives exclusively on a diet of blood:
  23. the vampire bat.
  24. These sorts of outbreaks
    that jump from bats into people,

  25. they've become more and more common
    in the last couple of decades.
  26. In 2003, it was SARS.
  27. It showed up in Chinese animal markets
    and spread globally.
  28. That virus, like the one from Peru,
    was eventually traced back to bats,
  29. which have probably harbored it,
    undetected, for centuries.
  30. Then, 10 years later, we see Ebola
    showing up in West Africa,
  31. and that surprised just about everybody
  32. because, according
    to the science at the time,
  33. Ebola wasn't really supposed
    to be in West Africa.
  34. That ended up causing the largest
    and most widespread Ebola outbreak
  35. in history.
  36. So there's a disturbing trend here, right?

  37. Deadly viruses are appearing in places
    where we can't really expect them,
  38. and as a global health community,
  39. we're caught on our heels.
  40. We're constantly chasing
    after the next viral emergency
  41. in this perpetual cycle,
  42. always trying to extinguish epidemics
    after they've already started.
  43. So with new diseases appearing every year,
  44. now is really the time
  45. that we need to start thinking
    about what we can do about it.
  46. If we just wait for the next
    Ebola to happen,
  47. we might not be so lucky next time.
  48. We might face a different virus,
  49. one that's more deadly,
  50. one that spreads better among people,
  51. or maybe one that just completely
    outwits our vaccines,
  52. leaving us defenseless.
  53. So can we anticipate pandemics?

  54. Can we stop them?
  55. Those are really hard questions to answer,
  56. and the reason is that the pandemics --
  57. the ones that spread globally,
  58. the ones that we really
    want to anticipate --
  59. they're actually really rare events.
  60. And for us as a species
    that is a good thing --
  61. that's why we're all here.
  62. But from a scientific standpoint,
    it's a little bit of a problem.
  63. That's because if something
    happens just once or twice,
  64. that's really not enough
    to find any patterns.
  65. Patterns that could tell us when
    or where the next pandemic might strike.
  66. So what do we do?
  67. Well, I think one of the solutions
    we may have is to study some viruses
  68. that routinely jump from wild
    animals into people,
  69. or into our pets, or our livestock,
  70. even if they're not the same viruses
  71. that we think are going
    to cause pandemics.
  72. If we can use
    those everyday killer viruses
  73. to work out some of the patterns
  74. of what drives that initial, crucial jump
    from one species to the next,
  75. and, potentially, how we might stop it,
  76. then we're going to end up better prepared
  77. for those viruses that jump
    between species more rarely
  78. but pose a greater threat of pandemics.
  79. Now, rabies, as terrible as it is,

  80. turns out to be a pretty nice
    virus in this case.
  81. You see, rabies is a scary, deadly virus.
  82. It has 100 percent fatality.
  83. That means if you get infected with rabies
    and you don't get treated early,
  84. there's nothing that can be done.
  85. There is no cure.
  86. You will die.
  87. And rabies is not just
    a problem of the past either.
  88. Even today, rabies still kills
    50 to 60,000 people every year.
  89. Just put that number in some perspective.
  90. Imagine the whole West African
    Ebola outbreak --
  91. about two-and-a-half years;
  92. you condense all the people
    that died in that outbreak
  93. into just a single year.
  94. That's pretty bad.
  95. But then, you multiply it by four,
  96. and that's what happens
    with rabies every single year.
  97. So what sets rabies apart
    from a virus like Ebola

  98. is that when people get it,
  99. they tend not to spread it onward.
  100. That means that every single time
    a person gets rabies,
  101. it's because they were bitten
    by a rabid animal,
  102. and usually, that's a dog or a bat.
  103. But it also means that those jumps
    between species,
  104. which are so important to understand,
    but so rare for most viruses,
  105. for rabies, they're actually
    happening by the thousands.
  106. So in a way, rabies
    is almost like the fruit fly
  107. or the lab mouse of deadly viruses.
  108. This is a virus that we can use
    and study to find patterns
  109. and potentially test out new solutions.
  110. And so, when I first heard
    about that outbreak of rabies
  111. in the Peruvian Amazon,
  112. it struck me as something
    potentially powerful
  113. because this was a virus that was jumping
    from bats into other animals
  114. often enough that we might
    be able to anticipate it ...
  115. Maybe even stop it.
  116. So as a first-year graduate student

  117. with a vague memory
    of my high school Spanish class,
  118. I jumped onto a plane
    and flew off to Peru,
  119. looking for vampire bats.
  120. And the first couple of years
    of this project were really tough.
  121. I had no shortage of ambitious plans
    to rid Latin America of rabies,
  122. but at the same time,
  123. there seemed to be an equally endless
    supply of mudslides and flat tires,
  124. power outages, stomach bugs
    all stopping me.
  125. But that was kind of par for the course,
  126. working in South America,
  127. and to me, it was part of the adventure.
  128. But what kept me going
  129. was the knowledge that for the first time,
  130. the work that I was doing
    might actually have some real impact
  131. on people's lives in the short term.
  132. And that struck me the most
  133. when we actually went out to the Amazon
  134. and were trying to catch vampire bats.
  135. You see, all we had to do was show up
    at a village and ask around.
  136. "Who's been getting bitten
    by a bat lately?"
  137. And people raised their hands,
  138. because in these communities,
  139. getting bitten by a bat
    is an everyday occurrence,
  140. happens every day.
  141. And so all we had to do
    was go to the right house,
  142. open up a net
  143. and show up at night,
  144. and wait until the bats tried
    to fly in and feed on human blood.
  145. So to me, seeing a child with a bite wound
    on his head or blood stains on his sheets,
  146. that was more than enough motivation
  147. to get past whatever logistical
    or physical headache
  148. I happened to be feeling on that day.
  149. Since we were working
    all night long, though,

  150. I had plenty of time to think about
    how I might actually solve this problem,
  151. and it stood out to me
    that there were two burning questions.
  152. The first was that we know
    that people are bitten all the time,
  153. but rabies outbreaks
    aren't happening all the time --
  154. every couple of years,
    maybe even every decade,
  155. you get a rabies outbreak.
  156. So if we could somehow anticipate
    when and where the next outbreak would be,
  157. that would be a real opportunity,
  158. meaning we could vaccinate
    people ahead of time,
  159. before anybody starts dying.
  160. But the other side of that coin
  161. is that vaccination
    is really just a Band-Aid.
  162. It's kind of a strategy of damage control.
  163. Of course it's lifesaving and important
    and we have to do it,
  164. but at the end of the day,
  165. no matter how many cows,
    how many people we vaccinate,
  166. we're still going to have exactly the same
    amount of rabies up there in the bats.
  167. The actual risk of getting bitten
    hasn't changed at all.
  168. So my second question was this:
  169. Could we somehow
    cut the virus off at its source?
  170. If we could somehow reduce the amount
    of rabies in the bats themselves,
  171. then that would be a real game changer.
  172. We'd been talking about shifting

  173. from a strategy of damage control
    to one based on prevention.
  174. So, how do we begin to do that?
  175. Well, the first thing
    we needed to understand
  176. was how this virus actually works
    in its natural host --
  177. in the bats.
  178. And that is a tall order
    for any infectious disease,
  179. particularly one in a reclusive
    species like bats,
  180. but we had to start somewhere.
  181. So the way we started
    was looking at some historical data.
  182. When and where had these outbreaks
    happened in the past?
  183. And it became clear
    that rabies was a virus
  184. that just had to be on the move.
  185. It couldn't sit still.
  186. The virus might circulate in one area
    for a year, maybe two,
  187. but unless it found a new group of bats
    to infect somewhere else,
  188. it was pretty much bound to go extinct.
  189. So with that, we solved one key part
    of the rabies transmission challenge.
  190. We knew we were dealing
    with a virus on the move,
  191. but we still couldn't say
    where it was going.
  192. Essentially, what I wanted was
    more of a Google Maps-style prediction,

  193. which is, "What's
    the destination of the virus?
  194. What's the route it's going
    to take to get there?
  195. How fast will it move?"
  196. To do that, I turned
    to the genomes of rabies.
  197. You see, rabies, like many other viruses,
    has a tiny little genome,
  198. but one that evolves
    really, really quickly.
  199. So quickly that by the time the virus
    has moved from one point to the next,
  200. it's going to have picked up
    a couple of new mutations.
  201. And so all we have to do
    is kind of connect the dots
  202. across an evolutionary tree,
  203. and that's going to tell us
    where the virus has been in the past
  204. and how it spread across the landscape.
  205. So, I went out and I collected cow brains,
  206. because that's where
    you get rabies viruses.
  207. And from genome sequences that we got
    from the viruses in those cow brains,
  208. I was able to work out
  209. that this is a virus that spreads
    between 10 and 20 miles each year.
  210. OK, so that means we do now have
    the speed limit of the virus,

  211. but still missing that other key part
    of where is it going in the first place.
  212. For that, I needed to think
    a little bit more like a bat,
  213. because rabies is a virus --
  214. it doesn't move by itself,
  215. it has to be moved around by its bat host,
  216. so I needed to think about
    how far to fly and how often to fly.
  217. My imagination didn't get me
    all that far with this
  218. and neither did little digital trackers
    that we first tried putting on bats.
  219. We just couldn't get
    the information we needed.
  220. So instead, we turned
    to the mating patterns of bats.
  221. We could look at certain parts
    of the bat genome,
  222. and they were telling us that some
    groups of bats were mating with each other
  223. and others were more isolated.
  224. And the virus was basically following
    the trail laid out by the bat genomes.
  225. Yet one of those trails stood out
    as being a little bit surprising --
  226. hard to believe.
  227. That was one that seemed to cross
    straight over the Peruvian Andes,
  228. crossing from the Amazon
    to the Pacific coast,
  229. and that was kind of hard to believe,
  230. as I said,
  231. because the Andes are really tall --
    about 22,000 feet,
  232. and that's way too high
    for a vampire to fly.
  233. Yet --
  234. (Laughter)

  235. when we looked more closely,

  236. we saw, in the northern part of Peru,
  237. a network of valley systems
    that was not quite too tall
  238. for the bats on either side
    to be mating with each other.
  239. And we looked a little bit more closely --
  240. sure enough, there's rabies
    spreading through those valleys,
  241. just about 10 miles each year.
  242. Basically, exactly as our evolutionary
    models had predicated it would be.
  243. What I didn't tell you

  244. is that that's actually
    kind of an important thing
  245. because rabies had never been seen before
    on the western slopes of the Andes,
  246. or on the whole Pacific coast
    of South America,
  247. so we were actually witnessing,
    in real time, a historical first invasion
  248. into a pretty big part of South America,
  249. which raises the key question:
  250. "What are we going to do about that?"
  251. Well, the obvious short-term
    thing we can do is tell people:

  252. you need to vaccinate yourselves,
    vaccinate your animals;
  253. rabies is coming.
  254. But in the longer term,
  255. it would be even more powerful
    if we could use that new information
  256. to stop the virus
    from arriving altogether.
  257. Of course, we can't just tell bats,
    "Don't fly today,"
  258. but maybe we could stop the virus
    from hitching a ride along with the bat.
  259. And that brings us to the key lesson
    that we have learned

  260. from rabies-management programs
    all around the world,
  261. whether it's dogs, foxes,
    skunks, raccoons,
  262. North America, Africa, Europe.
  263. It's that vaccinating the animal source
    is the only thing that stops rabies.
  264. So, can we vaccinate bats?

  265. You hear about vaccinating dogs
    and cats all the time,
  266. but you don't hear too much
    about vaccinating bats.
  267. It might sound like a crazy question,
  268. but the good news is that we actually
    already have edible rabies vaccines
  269. that are specially designed for bats.
  270. And what's even better
  271. is that these vaccines
    can actually spread from bat to bat.
  272. All you have to do is smear it on one
  273. and let the bats' habit
    of grooming each other
  274. take care of the rest of the work for you.
  275. So that means, at the very least,
  276. we don't have to be out there vaccinating
    millions of bats one by one
  277. with tiny little syringes.
  278. (Laughter)

  279. But just because we have that tool
    doesn't mean we know how to use it.

  280. Now we have a whole laundry
    list of questions.
  281. How many bats do we need to vaccinate?
  282. What time of the year
    do we need to be vaccinating?
  283. How many times a year
    do we need to be vaccinating?
  284. All of these are questions
    that are really fundamental
  285. to rolling out any sort
    of vaccination campaign,
  286. but they're questions
    that we can't answer in the laboratory.
  287. So instead, we're taking
    a slightly more colorful approach.
  288. We're using real wild bats,
    but fake vaccines.
  289. We use edible gels that make bat hair glow
  290. and UV powders that spread between
    bats when they bump into each other,
  291. and that's letting us study
    how well a real vaccine might spread
  292. in these wild colonies of bats.
  293. We're still in the earliest
    phases of this work,
  294. but our results so far
    are incredibly encouraging.
  295. They're suggesting that using
    the vaccines that we already have,
  296. we could potentially drastically reduce
    the size of rabies outbreaks.
  297. And that matters, because as you remember,
  298. rabies is a virus that always
    has to be on the move,
  299. and so every time we reduce
    the size of an outbreak,
  300. we're also reducing the chance
  301. that the virus makes it
    onto the next colony.
  302. We're breaking a link
    in the chain of transmission.
  303. And so every time we do that,
  304. we're bringing the virus
    one step closer to extinction.
  305. And so the thought, for me,
    of a world in the not-too-distant future
  306. where we're actually talking
    about getting rid of rabies altogether,
  307. that is incredibly
    encouraging and exciting.
  308. So let me return to the original question.

  309. Can we prevent pandemics?
  310. Well, there is no silver-bullet
    solution to this problem,
  311. but my experiences with rabies
    have left me pretty optimistic about it.
  312. I think we're not too far from a future
  313. where we're going to have genomics
    to forecast outbreaks
  314. and we're going to have clever
    new technologies,
  315. like edible, self-spreading vaccines,
  316. that can get rid of these
    viruses at their source
  317. before they have a chance
    to jump into people.
  318. So when it comes to fighting pandemics,

  319. the holy grail is just to get
    one step ahead.
  320. And if you ask me,
  321. I think one of the ways
    that we can do that
  322. is using some of the problems
    that we already have now,
  323. like rabies --
  324. sort of the way an astronaut
    might use a flight simulator,
  325. figuring out what works and what doesn't,
  326. and building up our tool set
  327. so that when the stakes are high,
  328. we're not flying blind.
  329. Thank you.

  330. (Applause)