The oldest human disease is more than 10 million years old and it's surviving because it is a master of disguise, according to scientists at the University of Texas MD Anderson Cancer Center.

Leprosy has plagued humankind for thousands of years and despite available treatments, still affects hundreds of thousands of people worldwide each year.

It attacks a patient's skin and nerves and if left untreated it can lead to extensive skin lesions, deformities and death.

In studies going back 10 years, Texas researchers have figured out how it has survived and plan to use their findings to fight it and many other diseases.

"It has developed a parasitic adaptive quality within our body," said MD Anderson pathologist Xiang-Yang Han, who led the research. "Like a cat chasing a mouse, we chase it and it goes and hides."

Diseases carry antigens, which our immune systems use to find and kill foreign cells.

Dr. Han and his team found leprosy is five times more likely to be able to switch off the most significant antigens, eluding our immune systems to survive. 

"What we need to ask now is how did it deactivate those antigens and why? And then we can say, those antigens might be helpful to us." said Dr. Han.

The new findings also reveal current leprosy bacterias date back 10 million years, making it the oldest known disease, with ancestors dating back up to 20 million.

It first lived freely in the atmosphere before taking on human hosts among our early ancestors.  The only other species affected is armadillos, and it's thought they caught it from early American explorers.

Scientists say in concept we might be able to take this understanding to build new tools to help fight all diseases.

"The more we understand the origins of a disease, the more we understand the whole picture," said Dr. Han.