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The story that I'm going to tell you today,
for me, began back in 2006.
That was when I first heard about an outbreak of mysterious illness
that was happening in the Amazon rainforest of Peru.
The people that were getting sick from this illness,
they had horrifying symptoms, nightmarish.
They had unbelievable headaches,
they couldn't eat or drink.
Some of them were even hallucinating --
confused and aggressive.
The most tragic part of all
was that many of the victims were children.
And of all of those that got sick,
none survived.
It turned out that what was killing people was a virus,
but it wasn't Ebola, it wasn't Zika,
it wasn't even some new virus never before seen by science.
These people were dying of an ancient killer,
one that we've known about for centuries.
They were dying of rabies.
And what all of them had in common was that as they slept,
they'd all been bitten by the only mammal that lives exclusively on a diet of blood:
the vampire bat.
These sorts of outbreaks that jump from bats into people,
they've become more and more common in the last couple of decades.
In 2003, it was SARS.
It showed up in Chinese animal markets and spread globally.
That virus, like the one from Peru, was eventually traced back to bats,
which have probably harbored it, undetected, for centuries.
Then, 10 years later, we see Ebola showing up in West Africa,
and that surprised just about everybody
because, according to the science at the time,
Ebola wasn't really supposed to be in West Africa.
That ended up causing the largest and most widespread Ebola outbreak
in history.
So there's a disturbing trend here, right?
Deadly viruses are appearing in places where we can't really expect them,
and as a global health community,
we're caught on our heels.
We're constantly chasing after the next viral emergency
in this perpetual cycle,
always trying to extinguish epidemics after they've already started.
So with new diseases appearing every year,
now is really the time
that we need to start thinking about what we can do about it.
If we just wait for the next Ebola to happen,
we might not be so lucky next time.
We might face a different virus,
one that's more deadly,
one that spreads better among people,
or maybe one that just completely outwits our vaccines,
leaving us defenseless.
So can we anticipate pandemics?
Can we stop them?
Those are really hard questions to answer,
and the reason is that the pandemics --
the ones that spread globally,
the ones that we really want to anticipate --
they're actually really rare events.
And for us as a species that is a good thing --
that's why we're all here.
But from a scientific standpoint, it's a little bit of a problem.
That's because if something happens just once or twice,
that's really not enough to find any patterns.
Patterns that could tell us when or where the next pandemic might strike.
So what do we do?
Well, I think one of the solutions we may have is to study some viruses
that routinely jump from wild animals into people,
or into our pets, or our livestock,
even if they're not the same viruses
that we think are going to cause pandemics.
If we can use those everyday killer viruses
to work out some of the patterns
of what drives that initial, crucial jump from one species to the next,
and, potentially, how we might stop it,
then we're going to end up better prepared
for those viruses that jump between species more rarely
but pose a greater threat of pandemics.
Now, rabies, as terrible as it is,
turns out to be a pretty nice virus in this case.
You see, rabies is a scary, deadly virus.
It has 100 percent fatality.
That means if you get infected with rabies and you don't get treated early,
there's nothing that can be done.
There is no cure.
You will die.
And rabies is not just a problem of the past either.
Even today, rabies still kills 50 to 60,000 people every year.
Just put that number in some perspective.
Imagine the whole West African Ebola outbreak --
about two-and-a-half years;
you condense all the people that died in that outbreak
into just a single year.
That's pretty bad.
But then, you multiply it by four,
and that's what happens with rabies every single year.
So what sets rabies apart from a virus like Ebola
is that when people get it,
they tend not to spread it onward.
That means that every single time a person gets rabies,
it's because they were bitten by a rabid animal,
and usually, that's a dog or a bat.
But it also means that those jumps between species,
which are so important to understand, but so rare for most viruses,
for rabies, they're actually happening by the thousands.
So in a way, rabies is almost like the fruit fly
or the lab mouse of deadly viruses.
This is a virus that we can use and study to find patterns
and potentially test out new solutions.
And so, when I first heard about that outbreak of rabies
in the Peruvian Amazon,
it struck me as something potentially powerful
because this was a virus that was jumping from bats into other animals
often enough that we might be able to anticipate it ...
Maybe even stop it.
So as a first-year graduate student
with a vague memory of my high school Spanish class,
I jumped onto a plane and flew off to Peru,
looking for vampire bats.
And the first couple of years of this project were really tough.
I had no shortage of ambitious plans to rid Latin America of rabies,
but at the same time,
there seemed to be an equally endless supply of mudslides and flat tires,
power outages, stomach bugs all stopping me.
But that was kind of par for the course,
working in South America,
and to me, it was part of the adventure.
But what kept me going
was the knowledge that for the first time,
the work that I was doing might actually have some real impact
on people's lives in the short term.
And that struck me the most
when we actually went out to the Amazon
and were trying to catch vampire bats.
You see, all we had to do was show up at a village and ask around.
"Who's been getting bitten by a bat lately?"
And people raised their hands,
because in these communities,
getting bitten by a bat is an everyday occurrence,
happens every day.
And so all we had to do was go to the right house,
open up a net
and show up at night,
and wait until the bats tried to fly in and feed on human blood.
So to me, seeing a child with a bite wound on his head or blood stains on his sheets,
that was more than enough motivation
to get past whatever logistical or physical headache
I happened to be feeling on that day.
Since we were working all night long, though,
I had plenty of time to think about how I might actually solve this problem,
and it stood out to me that there were two burning questions.
The first was that we know that people are bitten all the time,
but rabies outbreaks aren't happening all the time --
every couple of years, maybe even every decade,
you get a rabies outbreak.
So if we could somehow anticipate when and where the next outbreak would be,
that would be a real opportunity,
meaning we could vaccinate people ahead of time,
before anybody starts dying.
But the other side of that coin
is that vaccination is really just a Band-Aid.
It's kind of a strategy of damage control.
Of course it's lifesaving and important and we have to do it,
but at the end of the day,
no matter how many cows, how many people we vaccinate,
we're still going to have exactly the same amount of rabies up there in the bats.
The actual risk of getting bitten hasn't changed at all.
So my second question was this:
Could we somehow cut the virus off at its source?
If we could somehow reduce the amount of rabies in the bats themselves,
then that would be a real game changer.
We'd been talking about shifting
from a strategy of damage control to one based on prevention.
So, how do we begin to do that?
Well, the first thing we needed to understand
was how this virus actually works in its natural host --
in the bats.
And that is a tall order for any infectious disease,
particularly one in a reclusive species like bats,
but we had to start somewhere.
So the way we started was looking at some historical data.
When and where had these outbreaks happened in the past?
And it became clear that rabies was a virus
that just had to be on the move.
It couldn't sit still.
The virus might circulate in one area for a year, maybe two,
but unless it found a new group of bats to infect somewhere else,
it was pretty much bound to go extinct.
So with that, we solved one key part of the rabies transmission challenge.
We knew we were dealing with a virus on the move,
but we still couldn't say where it was going.
Essentially, what I wanted was more of a Google Maps-style prediction,
which is, "What's the destination of the virus?
What's the route it's going to take to get there?
How fast will it move?"
To do that, I turned to the genomes of rabies.
You see, rabies, like many other viruses, has a tiny little genome,
but one that evolves really, really quickly.
So quickly that by the time the virus has moved from one point to the next,
it's going to have picked up a couple of new mutations.
And so all we have to do is kind of connect the dots
across an evolutionary tree,
and that's going to tell us where the virus has been in the past
and how it spread across the landscape.
So, I went out and I collected cow brains,
because that's where you get rabies viruses.
And from genome sequences that we got from the viruses in those cow brains,
I was able to work out
that this is a virus that spreads between 10 and 20 miles each year.
OK, so that means we do now have the speed limit of the virus,
but still missing that other key part of where is it going in the first place.
For that, I needed to think a little bit more like a bat,
because rabies is a virus --
it doesn't move by itself,
it has to be moved around by its bat host,
so I needed to think about how far to fly and how often to fly.
My imagination didn't get me all that far with this
and neither did little digital trackers that we first tried putting on bats.
We just couldn't get the information we needed.
So instead, we turned to the mating patterns of bats.
We could look at certain parts of the bat genome,
and they were telling us that some groups of bats were mating with each other
and others were more isolated.
And the virus was basically following the trail laid out by the bat genomes.
Yet one of those trails stood out as being a little bit surprising --
hard to believe.
That was one that seemed to cross straight over the Peruvian Andes,
crossing from the Amazon to the Pacific coast,
and that was kind of hard to believe,
as I said,
because the Andes are really tall -- about 22,000 feet,
and that's way too high for a vampire to fly.
Yet --
(Laughter)
when we looked more closely,
we saw, in the northern part of Peru,
a network of valley systems that was not quite too tall
for the bats on either side to be mating with each other.
And we looked a little bit more closely --
sure enough, there's rabies spreading through those valleys,
just about 10 miles each year.
Basically, exactly as our evolutionary models had predicated it would be.
What I didn't tell you
is that that's actually kind of an important thing
because rabies had never been seen before on the western slopes of the Andes,
or on the whole Pacific coast of South America,
so we were actually witnessing, in real time, a historical first invasion
into a pretty big part of South America,
which raises the key question:
"What are we going to do about that?"
Well, the obvious short-term thing we can do is tell people:
you need to vaccinate yourselves, vaccinate your animals;
rabies is coming.
But in the longer term,
it would be even more powerful if we could use that new information
to stop the virus from arriving altogether.
Of course, we can't just tell bats, "Don't fly today,"
but maybe we could stop the virus from hitching a ride along with the bat.
And that brings us to the key lesson that we have learned
from rabies-management programs all around the world,
whether it's dogs, foxes, skunks, raccoons,
North America, Africa, Europe.
It's that vaccinating the animal source is the only thing that stops rabies.
So, can we vaccinate bats?
You hear about vaccinating dogs and cats all the time,
but you don't hear too much about vaccinating bats.
It might sound like a crazy question,
but the good news is that we actually already have edible rabies vaccines
that are specially designed for bats.
And what's even better
is that these vaccines can actually spread from bat to bat.
All you have to do is smear it on one
and let the bats' habit of grooming each other
take care of the rest of the work for you.
So that means, at the very least,
we don't have to be out there vaccinating millions of bats one by one
with tiny little syringes.
(Laughter)
But just because we have that tool doesn't mean we know how to use it.
Now we have a whole laundry list of questions.
How many bats do we need to vaccinate?
What time of the year do we need to be vaccinating?
How many times a year do we need to be vaccinating?
All of these are questions that are really fundamental
to rolling out any sort of vaccination campaign,
but they're questions that we can't answer in the laboratory.
So instead, we're taking a slightly more colorful approach.
We're using real wild bats, but fake vaccines.
We use edible gels that make bat hair glow
and UV powders that spread between bats when they bump into each other,
and that's letting us study how well a real vaccine might spread
in these wild colonies of bats.
We're still in the earliest phases of this work,
but our results so far are incredibly encouraging.
They're suggesting that using the vaccines that we already have,
we could potentially drastically reduce the size of rabies outbreaks.
And that matters, because as you remember,
rabies is a virus that always has to be on the move,
and so every time we reduce the size of an outbreak,
we're also reducing the chance
that the virus makes it onto the next colony.
We're breaking a link in the chain of transmission.
And so every time we do that,
we're bringing the virus one step closer to extinction.
And so the thought, for me, of a world in the not-too-distant future
where we're actually talking about getting rid of rabies altogether,
that is incredibly encouraging and exciting.
So let me return to the original question.
Can we prevent pandemics?
Well, there is no silver-bullet solution to this problem,
but my experiences with rabies have left me pretty optimistic about it.
I think we're not too far from a future
where we're going to have genomics to forecast outbreaks
and we're going to have clever new technologies,
like edible, self-spreading vaccines,
that can get rid of these viruses at their source
before they have a chance to jump into people.
So when it comes to fighting pandemics,
the holy grail is just to get one step ahead.
And if you ask me,
I think one of the ways that we can do that
is using some of the problems that we already have now,
like rabies --
sort of the way an astronaut might use a flight simulator,
figuring out what works and what doesn't,
and building up our tool set
so that when the stakes are high,
we're not flying blind.
Thank you.
(Applause)
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【TED】What vaccinating vampire bats can teach us about pandemics | Daniel Streicker

160 タグ追加 保存
林宜悉 2019 年 11 月 24 日 に公開
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