The bacterium that causes leprosy is genetically stable, which makes curing the disease easier, a Swiss-led research team says.

The project, headed by Stewart Cole of the Federal Institute of Technology in Lausanne, found samples of mycobacterium leprae from around the world, Swissinfo reported. The oldest was found in an Egyptian mummy buried about 2,400 years ago.

There are four strains of the bacterium -- European, Indian and East and West African -- with only small genetic differences among them.

"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," Cole said. "This is very good news in terms of treatment."

While an antibiotic cure for leprosy has been available for 30 years and is free, about 700,000 people worldwide are infected with the disease. The World Health Organization said 250,000 new cases were diagnosed in 2008.