Image copyright RTI International/Louise Gubb Image caption More people are now getting treatment for lymphatic filariasis which makes limbs swell

There has been a record-breaking achievement in distributing tablets to fight neglected tropical diseases, the Bill and Melinda Gates Foundation says.

The effort has ramped up since a key meeting in London five years ago.

In 2015, one billion people worldwide were treated for at least one tropical disease. Companies have donated seven billion treatments since 2012.

The World Health Organisation said improving water and sanitation was key to driving further progress.

The London meeting resulted in a pledge to control or eliminate 10 neglected tropical diseases - including guinea worm, river blindness and trachoma - by 2020.

Some 170,000 people die from one of the illnesses every year, but their biggest impact is disabling their sufferers.

In an interview with BBC News, Bill Gates praised pharmaceutical companies for "doing their part in a great relationship" by donating treatment at "a phenomenal scale".

'Fantastic story'

Mr Gates said: "None of these diseases are getting worse. They are less neglected than they used to be.

"We're behind on some of the very ambitious goals which were set in London for 2020 - but the burden from all these diseases is getting better.

"And for some, such as lymphatic filariasis (a mosquito-borne worm which causes limbs to swell), there's been a big reduction in the population we need to treat - from 1.5 billion to one billion people.

"Guinea worm is close to the end, with only 25 cases last year - though the unrest in South Sudan is making this work harder. But it's not going to spread back in big numbers.

"And we've had huge progress on sleeping sickness (a parasitic infection which can kill) - with cases now down to under 3,000. This is a fantastic story.

"It's a hard area to explain because it's not just one disease - and there is a certain complexity to the individual diseases."

Five of the 10 diseases are tackled with big programmes to distribute multiple drugs, requiring lots of co-ordination to deliver and evaluate treatment in an efficient way.

Mr Gates was speaking from a meeting in Geneva, where new commitments worth $812m (£641m) have been made by governments, drug companies and charitable bodies.

He applauded the UK government's announcement at the weekend that it would double support for fighting neglected tropical diseases.

Mr Gates told me: "The UK is a critical donor. As somebody who's very measurement-oriented, I find that partnering with the UK on these health-related areas is a great way to spend money and lift these countries up.

"Anyone who gets to see these very tough diseases, and to see the benefit from these initiatives, would be absolutely convinced."

President Trump 'pragmatic'

Mr Gates, who had a meeting with President Trump last month, described the recent US funding cut to the United Nations Population Fund as "disappointing and unfortunate".

He added: "I feel quite confident that when Congress decides the overall aid budget, there won't be the large cuts to foreign aid that would have been implied by the President's proposed budget.

"I don't know that we'll get to a situation where there are no cuts - but I think with the support of Congress, we'll get close to where we've been in previous years.

"I talked to the President about the critical role the US has played in the great progress on HIV, malaria and reproductive health - and in terms of how strong health systems can stop pandemics.

"We got a glimpse of that with Ebola and Zika.

"I think I was able to get across the idea that global health matters even in an 'America First' framework.

"The President has proved willing to be pragmatic since he's been in office - so continued dialogue about development aid will be important."