A Swiss-led team of international scientists hopes its study retracing the history of leprosy from ancient Egypt to today can help contribute to the elimination of the debilitating illness, which still persists among the world's poor.

The researchers examined DNA from human remains from different parts of the world, including Brazil, Madagascar, China, Europe and Egypt, where they unearthed a fourth-century BC mummy.

They identified four strains of mycobacterium leprae, the bacterium that causes leprosy: European, Indian, East African and West African, with small variations between them.

Stewart Cole, a professor from Lausanne's Federal Institute of Technology (EPFL) who led the study, described leprosy as "one of the most stable organisms" he has ever observed.

"Irrespective of the origin of the sample of mycobacterium leprae, there was a remarkably high level of similarity and the genome was extremely well conserved," he told swissinfo.ch.

"This is very good news in terms of treatment."

Only a hundred different variations exist between the DNA of two different strains, whereas with HIV or flu there may be thousands of mutations.

Frequent transformations often lead to disturbing resistances to antibiotic treatments, such as with tuberculosis. A more stable bacterium responds more efficiently to treatment, indicated the study, which was published in the latest edition of Nature Genetics journal.

Tremendous progress

In 1996 the World Health Organization (WHO) said it hoped to all but eliminate leprosy within ten years.

Overall numbers are in decline, but the disease remains a persistent health issue, with over 700,000 people infected worldwide.

"There has been tremendous progress - over 12 million patients cured," said Cole. "But there are still a lot of infectious individuals or other sources around and these need to be mopped up."

According to WHO, some 250,000 new cases in South America, Asia and Africa were diagnosed in 2008, even though a cure, which is available free, was found more than 20 years ago.

Leprosy is a relatively easy disease to cure if the patients are identified early enough and provided the patients take their treatment properly and for the full duration, said the EPFL professor.

Complicated treatment

The effective multi-drug therapy developed by WHO involves taking three antibiotics for a period of between one to two years depending on the form of leprosy.

Once a person is treated, within a few weeks he is no longer contagious but physical deformities, including damaged hands and feet, remain.

"It's a complicated treatment. Ideally, we'd like to find new drugs that act more quickly so patients don't have to be observed for such a long time and it's less onerous for them," said Cole.

But leprosy is a neglected disease, with only a few ongoing research projects due to limited funding and a greater focus on tuberculosis, he added.

Far from over

"It's important that there should be active research into leprosy, as it's far from certain that the disease will be eliminated," said Cole.

WHO spokesperson Francesco Rio agreed the fight was far from over.

"The last mile is the toughest – this has been shown with other diseases like guinea worm or polio," he told swissinfo.ch. "The end of an elimination campaign is when you need to put more effort as the cost per capita increases."

"We need to keep up the pressure on states as leprosy can come back," he said.

Simon Bradley, swissinfo.ch