Image copyright Louise Gubb for the Carter Cente Image caption Former president Jimmy Carter comforts six-year-old Ruhama Issah at Savelugu (Ghana) Hospital as she is treated for Guinea worm.

There were just 22 cases of the devastating Guinea worm disease in 2015, according to a human rights organisation.

The Carter Centre, which was set up by former President Jimmy Carter, said that represented a 83% drop from the 126 cases reported last year.

Guinea worm isn't deadly, but it is extremely painful and stops people in some of the world's poorest areas from going to work or school for months.

The former president said he wants it eradicated "next year or sooner after".

Guinea worm is particularly nasty.

It's carried by tiny water flies which sit in stagnant water. When people drink that water the Guinea worm larvae enters the body and starts maturing into a worm.

After about a year, when it's grown to around a meter long, it starts burrowing through the body and eventually causes a painful blister on the skin's surface.

Image copyright Louise Gubb for the Carter Cente

Image copyright Carter Center Image caption Guinea worms in a jar

It can then take a few days or weeks to fully emerge from the body, usually through the victim's leg or foot.

The Carter Centre has led the international effort against the disease, and the end game is very much in sight.

"This is a very exciting, challenging and sometimes frustrating experience for us," he said.

The former president made it his mission to wipe out the disease back in 1986.

Since then he said the number of countries reporting cases have gone from 21, to just four: Chad, Ethiopia, Mali and South Sudan.

Getting to Zero

"We hope this year we won't have any new cases, but if we do we'll just have to concentrate on those communities," said Mr Carter.

The former president said across those countries still affected there were actually only 20 villages and communities in the world which have cases of Guinea worm, although teams are still monitoring around 4,500 communities to ensure the disease doesn't come back.

"One person who goes into the water with a Guinea worm emerging can start the whole epidemic all over again," he said.

How to stop Guinea worm

Educate communities on not using water supplies to sooth Guinea worm blisters

Provide a clean water source

Filter water before drinking

Treat water with chemicals that kill the larvae

If the campaign is successful, Guinea worm will become only the second disease to ever be completely wiped out.

Smallpox was officially eradicated in 1980. Polio is also on the verge of being made extinct.

The British government has pledged another £4.5 million to efforts to finally end Guinea worm.

UK International Development Minister Nick Hurd said: "Guinea worm is a truly horrendous disease.

"The fact that we are now so close to eradicating it is one of the great public health success stories of modern times."

Mr Carter said around 88 million cases have been avoided in the last 30 years, meaning it's cost around $3 (£2) to prevent each case.

"Once we get rid of it, we'll never have to spend another dollar on the disease," he said.

One of the biggest threats to Guinea worm eradication is conflict, which stops health workers being able to go in and help affected communities.

Image copyright Louise Gubb for the Carter Cente Image caption Sadia Mesuna, 6, was successfully treated for Guinea worm at the Carter Center in Savelugu, Ghana

Mr Carter said another concern is dogs becoming infected and releasing larvae into water sources, which communities can then drink from, triggering a new cluster of cases.

The 39th president of the United States said achieving the eradication of Guinea worm would be his "most gratifying experience".

While emerging viruses such as Zika and before that Ebola have been causing a lot of concern, this is a timely reminder that complex and frightening diseases, can be beaten. The world is not there yet, but it is extremely close.

Mr Carter is already setting his sights on the next debilitating disease he wants to wipe out.

It's another neglected tropical disease called river blindness, spread by the bites of infected flies that breed in rapidly flowing rivers and can cause people to lose their sight.

He says eradication is possible. Watch this space.