Scientists say they have taken a major step towards the development of a vaccine for a neglected tropical disease that affects an estimated 17 million people globally.

Experiments have identified three potential vaccine compounds that could offer protection against river blindness, also known as onchocerciasis.

The condition is caused by infection with a parasitic worm and is spread by black flies that breed in rivers, with more than 90% of cases occurring in west and central Africa.

Around 10% of those infected develop eye conditions, 1% become blind and 70% develop severe skin diseases.

Researchers hope to take at least one of the potential vaccines to safety trials by 2020 and trials to test its effectiveness by 2025.

Lead researcher Professor David Taylor, from the University of Edinburgh's division of infection and pathway medicine, began work on the causes of river blindness in 1981.

He said: "New knowledge of the way nematode parasites regulate people's immune responses has guided formulation of experimental vaccines.

"A vaccine against river blindness would complement and augment existing treatment and significantly improve the prospects for eliminating this disease from Africa."

It is hoped that the vaccine will be used initially to protect vulnerable children in affected areas.

The research initiative, The Onchocerciasis Vaccine for Africa (Tova), was launched as a response to the London Declaration on Neglected Tropical Diseases which called for river blindness to be eliminated from Africa.

It builds on more than 30 years of research by Edinburgh academics and researchers in Africa, Europe and the US, and involves 15 organisations across five countries.