the infectious disease that's killed more humans

than any other is malaria.

It's carried in the bites of infected mosquitos,

and it's probably our oldest scourge.

We may have had malaria since we evolved from the apes.

And to this day, malaria takes a huge toll on our species.

We've got 300 million cases a year

and over half a million deaths.

Now this really makes no sense.

We've known how to cure malaria

since the 1600s.

That's when Jesuit missionaries in Peru

discovered the bark of the cinchona tree,

and inside that bark was quinine,

still an effective cure for malaria to this day.

So we've known how to cure malaria for centuries.

We've known how to prevent malaria since 1897.

That's when the British army surgeon Ronald Ross

discovered that it was mosquitos that carried malaria,

not bad air or miasmas, as was previously thought.

So malaria should be a relatively simple disease to solve,

and yet to this day, hundreds of thousands of people

are going to die from the bite of a mosquito.

Why is that?

This is a question that's

personally intrigued me for a long time.

I grew up as the daughter of Indian immigrants

visiting my cousins in India every summer,

and because I had no immunity to the local malarias,

I was made to sleep under this hot, sweaty mosquito net every night

while my cousins, they were allowed to sleep

out on the terrace and have

this nice, cool night breeze wafting over them.

And I really hated the mosquitos for that.

But at the same time, I come from a Jain family,

and Jainism is a religion that espouses

a very extreme form of nonviolence.

So Jains are not supposed to eat meat.

We're not supposed to walk on grass,

because you could, you know,

inadvertently kill some insects when you walk on grass.

We're certainly not supposed to swat mosquitos.

So the fearsome power of this little insect

was apparent to me from a very young age,

and it's one reason why I spent five years as a journalist

trying to understand, why has malaria

been such a horrible scourge for all of us for so very long?

And I think there's three main reasons why.

Those three reasons add up to the fourth reason,

which is probably the biggest reason of all.

The first reason is certainly scientific.

This little parasite that causes malaria,

it's probably one of the most complex

and wily pathogens known to humankind.

It lives half its life inside the cold-blooded mosquito

and half its life inside the warm-blooded human.

These two environments are totally different,

but not only that, they're both utterly hostile.

So the insect is continually trying to fight off the parasite,

and so is the human body continually trying to fight it off.

This little creature survives under siege like that,

but not only does it survive, it has thrived.

It has spread. It has more ways to evade attack than we know.

It's a shape-shifter, for one thing.

Just as a caterpillar turns into a butterfly,

the malaria parasite transforms itself like that

seven times in its life cycle.

And each of those life stages not only looks totally different from each other,

they have totally different physiology.

So say you came up with some great drug

that worked against one stage of the parasite's life cycle.

It might do nothing at all to any of the other stages.

It can hide in our bodies, undetected,

unbeknownst to us, for days, for weeks,

for months, for years, in some cases even decades.

So the parasite is a very big scientific challenge to tackle,

but so is the mosquito that carries the parasite.

Only about 12 species of mosquitos

carry most of the world's malaria,

and we know quite a bit about the kinds of

watery habitats that they specialize in.

So you might think, then, well, why don't we just

avoid the places where the killer mosquitos live? Right?

We could avoid the places where the killer grizzly bears live

and we avoid the places where the killer crocodiles live.

But say you live in the tropics

and you walk outside your hut one day

and you leave some footprints in the soft dirt

around your home.

Or say your cow does, or say your pig does,

and then, say, it rains,

and that footprint fills up with a little bit of water.

That's it. You've created the perfect

malarial mosquito habitat that's right outside your door.

So it's not easy for us to extricate ourselves from these insects.

We kind of create places that they love to live

just by living our own lives.

So there's a huge scientific challenge,

but there's a huge economic challenge too.

Malaria occurs in some of the poorest

and most remote places on Earth,

and there's a reason for that.

If you're poor, you're more likely to get malaria.

If you're poor, you're more likely to live

in rudimentary housing on marginal land that's poorly drained.

These are places where mosquitos breed.

You're less likely to have door screens or window screens.

You're less likely to have electricity

and all the indoor activities that electricity makes possible,

so you're outside more.

You're getting bitten by mosquitos more.

So poverty causes malaria,

but what we also know now is that malaria itself

causes poverty.

For one thing, it strikes hardest during harvest season,

so exactly when farmers need to be out in the fields

collecting their crops, they're home sick with a fever.

But it also predisposes people to death

from all other causes.

So this has happened historically.

We've been able to take malaria out of a society.

Everything else stays the same,

so we still have bad food, bad water, bad sanitation,

all the things that make people sick.

But just if you take malaria out,

deaths from everything else go down.

And the economist Jeff Sachs has actually quantified

what this means for a society.

What it means is, if you have malaria in your society,

your economic growth is depressed

by 1.3 percent every year,

year after year after year, just this one disease alone.

So this poses a huge economic challenge,

because say you do come up with your great drug

or your great vaccine -- how do you deliver it

in a place where there's no roads,

there's no infrastructure,

there's no electricity for refrigeration to keep things cold,

there's no clinics, there's no clinicians

to deliver these things where they're needed?

So there's a huge economic challenge in taming malaria.

But along with the scientific challenge and the economic challenge,

there's also a cultural challenge,

and this is probably the part about malaria

that people don't like to talk about.

And it's the paradox that the people

who have the most malaria in the world

tend to care about it the least.

This has been the finding of medical anthropologists again and again.

They ask people in malarious parts of the world,

"What do you think about malaria?"

And they don't say, "It's a killer disease. We're scared of it."

They say, "Malaria is a normal problem of life."

And that was certainly my personal experience.

When I told my relatives in India

that I was writing a book about malaria,

they kind of looked at me like

I told them I was writing a book about warts or something.

Like, why would you write about something so boring,

so ordinary? You know?

And it's simple risk perception, really.

A child in Malawi, for example,

she might have 12 episodes of malaria before the age of two,

but if she survives,

she'll continue to get malaria throughout her life,

but she's much less likely to die of it.

And so in her lived experience,

malaria is something that comes and goes.

And that's actually true for most of the world's malaria.

Most of the world's malaria comes and goes on its own.

It's just, there's so much malaria

that this tiny fraction of cases that end in death

add up to this big, huge number.

So I think people in malarious parts of the world

must think of malaria the way

those of us who live in the temperate world

think of cold and flu. Right?

Cold and flu have a huge burden on our societies

and on our own lives,

but we don't really even take

the most rudimentary precautions against it because

we consider it normal to get cold and flu

during cold and flu season.

And so this poses a huge cultural challenge in taming malaria,

because if people think it's normal to have malaria,

then how do you get them to run to the doctor

to get diagnosed, to pick up their prescription,

to get it filled, to take the drugs,

to put on the repellents, to tuck in the bed nets?

This is a huge cultural challenge in taming this disease.

So take all that together.

We've got a disease. It's scientifically complicated,

it's economically challenging to deal with,

and it's one for which the people who stand

to benefit the most care about it the least.

And that adds up to the biggest problem of all,

which, of course, is the political problem.

How do you get a political leader to do anything

about a problem like this?

And the answer is, historically, you don't.

Most malarious societies throughout history

have simply lived with the disease.

So the main attacks on malaria have come