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Nova ScienceNOW : 15 – Pandemic flu

November 9, 2019


ROBERT KRULWICH: So not only did a woodpecker
make news last year, birds themselves were a big item, very big: the subject of international
summits, White House conferences. I’m talking, of course, about bird flu. And very particularly,
I’m talking about something that probably hasn’t happened yet, but could. And that raises
a question. So far, this new bird flu has not acquired
the ability to travel on a cough or a sneeze, through the air, from one infected person
to another. But what everybody wants to know is, could it learn how? And what are the odds? Well, if you look at a virus, any virus, you’ll
find a recipe, a genetic recipe, a lot of instructions spelled out in chemicals, abbreviated
A, C, G and U. Everything a virus knows comes from these instructions. So somewhere in the
human virus there’s an instruction that says, “When you infect a person, infect him here
in the upper respiratory tractónot in the lungs, not in the tummyójust up here, and
make the person, the host cough.” ‘Cause what gets the virus out, it’s the way the virus
transmits. It’s different in a bird. In a bird flu, the
bird virus has an instruction that says “Infect the gut, and give the bird diarrhea, so it
leaves droppings.” And mostly it’s the droppings that transmit the virus for birds. So we do it here, they do it there. The bird
virus, therefore does not need an instruction for coughing and sneezing. But here’s the bad news: back in 1918 or so,
bird flu somehow acquired the gene for coughing and sneezing. It wasn’t much use, it just
sat there in birds. But when that virus got into people, that bird fluóbecause it could
pass through the airóthat flu killed 50 million people. So you may ask, “Well, in 1918, how
did that happen?” KANTA SUBBARAO: The 1918 viruses have acquired
the necessary characteristics to infect people and transmit efficiently. ROBERT KRULWICH: By accident? KANTA SUBBARAO: Un-huh. ROBERT KRULWICH: According to Kanta Subbarao,
one of the nation’s leading flu investigators, the 1918 bird flu got its cough and sneeze
transmissibility by mistake. It was a random event that happened kind of like this: are
you familiar with the old saw that if you put an infinite number of monkeys in front
of an infinite number of typewriters, you would eventually get Hamlet? KANTA SUBBARAO: I haven’t heard that. ROBERT KRULWICH: Okay, well let me explain
it a bit. Imagine one monkey hitting a typewriter at random; he doesn’t know what he’s typing.
But now, let’s make it an infinite number of monkeys. And infinite is a whole lot of
monkeys, so many that, eventually, some monkey somewhere is going to, completely at random,
produce a perfect copy of Hamlet. Well, in a similar manner, when one bird gets
sick with bird flu, as it gets sick, inside the bird the virus is spreading, copying itself
over and over and over, maybe a hundred million times. And if you’ve got a lot of birds, like
this crowd here, that means in all these animals, altogether there could be 10 trillion viruses.
So if you’re asking, “What are the chances of a bird flu accidentally creating the ability
to travel on a cough or a sneeze?” Well, it’s kind of like the monkeys and the typewriters. If you’re looking at 10 trillion viruses and
all you need is one mistake, just one, that spells out the right recipe, that could happen.
I mean, you’ve got 10 trillion chances. But here’s the big surprise. When I said to
Dr. Subbarao, “When we look at a human virus, do we know where in this sea of letters…would
you know where this cough and sneeze ability is?” KANTA SUBBARAO: Unfortunately not. ROBERT KRULWICH: Hasn’t it occurred to people
to try and figure it out? KANTA SUBBARAO: But it’s a difficult thing
to do. ROBERT KRULWICH: So scientists don’t know
if the recipe is a few letters longó very simpleóor if it’s thousands of letters long
and very complicated. KANTA SUBBARAO: Nobody’s sure yet. ROBERT KRULWICH: What you don’t know is a
lot. KANTA SUBBARAO: That’s true. ROBERT KRULWICH: Since we don’t know the recipe,
the genetic recipe, for coughing and sneezing, we can’t figure the odds. Try it yourself. Let’s say this guy’s chickens are all sick
with bird flu, and he’s got, let’s see, one, two, three, four, five chickens, which means…so
he’s sitting next to 500 million bird flu viruses. And I ask you, “What are the chances
there’s a cough and sneeze virus right here ready to infect him?” Well, if the recipe for coughing and sneezing
is 13 letters long, if it’s very simple, and there are 500 million viruses in his chickens?
Seems likely, kind of like just one of these monkeys accidentally typing a little bit of
Shakespeare, sure. But if the recipe for coughing and sneezing is 13,000 letters long, in a
very precise order, that’s like one monkey accidentally typing the first two acts of
Hamlet perfectly. Those are very different odds. So if we don’t know the recipe, we really
can’t know the odds. And remember, even if this chicken, or it could be a duck or a goose,
has randomly created the cough and sneeze virus, that virus still somehow has to get
from this bird to this man. KANTA SUBBARAO: That’s right. That’s right.
So there is, there are all these events that probability…has to sort of all come together:
the, the, the chance of the mutations and exposure to a susceptible host. ROBERT KRULWICH: This seems like such long
odds to me: got to have the sick duck, the sick duck has to be near a person who’s vulnerable,
the person has to suck in the virus, the virus has to attach. And yet it happened. It may
sound wildly improbable, but in 1918, it did happen, so there is a danger. But since we don’t know the recipe for coughing
and sneezing, when you read stories that seem to know the odds, that say the bird flu “is
coming,” or the worldwide pandemic is “inevitable,” or it’s “overdue,” or “around the corner,”
be skeptical. We know this flu is dangerous to birds. We don’t know if it’ll be dangerous
to humans tomorrow, or next year, or decades from now. We just don’t know.

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