This is The Guardian.

Imagine, a mysterious blister begins to form on your leg.

As it gets bigger and bigger, it gets more and more painful.

Constant agonising, burning.

And then, from its centre, a worm appears.

This is no alien creature pulled from sci-fi.

It's the guinea worm, a gruesome earthly parasite.

If you've never heard of it, that's for a good reason.

In 40 years, an eradication program has been able to bring down the annual number of infections

from 3.6 million to 10.

It's an incredible feat of public health, but the hardest challenge may lie ahead.

Getting to zero human cases is surprisingly difficult, perhaps impossible.

But why is that small jump such a big hurdle?

Today, the story of ending guinea worm,

and what it means to actually eradicate a disease.

I'm the Guardian science editor, Ian Sampal, and this is Science Weekly.

Maddie, the guinea worm.

From what I know, as internal parasites go, it's a pretty nasty one. Tell me about its

life cycle. It is nasty. So it's a nematode. That's basically round worms and eel worms. It's one of

the largest human parasitic worms. And the adult female can grow to between 60 and 80 centimetres and it starts its life cycle

in fresh water where it infects water fleas which are otherwise known as copepods and they're

basically tiny little crustaceans in the water. And people drink this water and they ingest

...