In a breakthrough, US researchers have found that an improved tuberculosis vaccine can offer strong protection against leprosy.

"This is the first study demonstrating that an improved vaccine against tuberculosis also offers cross-protection against Mycobacterium leprae, the causative agent of leprosy," said Marcus A. Horwitz, a professor of medicine and microbiology, immunology and molecular genetics from University of California Los Angeles.

That means that this vaccine has promise for better protecting against both major diseases at the same time.

"It also demonstrates that boosting a recombinant BCG vaccine further improves cross-protection against leprosy," Horwitz added.

In many parts of the world, leprosy and tuberculosis live side-by-side.

Worldwide, there are approximately 233,000 new cases of leprosy per year, with nearly all of them occurring where tuberculosis is endemic.

The currently available century-old vaccine Bacille Calmette-Guerin (BCG) provides only partial protection against both tuberculosis and leprosy.

In lab experiments over mice, researchers found that rBCG30, a recombinant variant of BCG that overexpresses a highly abundant 30 kDa protein of the tuberculosis bacterium known as Antigen 85B, is superior to BCG in protecting against tuberculosis in animal models, and also cross protects against leprosy.

In addition, they found that boosting rBCG30 with the antigen 85B protein - a protein also expressed by the leprosy bacillus - provides considerably stronger protection against leprosy.

The next step is to test the rBCG30 vaccine for efficacy in humans against TB.

"If it is effective against TB, then the next step would be to test its effectiveness in humans against leprosy," Horwitz noted in a paper published in the journal Infection and Immunity.