Leprosy, the disease that causes skin lesions and eventually permanent disfigurement, was a constant threat in Medieval Europe, with as many as one in 30 people infected in some areas. But something remarkable happened around the mid 1500s — disease rates dropped sharply, according to historical records, although scientists were not quite sure why. Now an international team of researchers has uncovered DNA evidence that suggests humans rapidly evolved to fight off the disease.

The scientists came up with the theory after examining ancient human remains, scraping the bones for dead Medieval leprosy bacteria. They then managed to take bacteria and reconstruct its entire genome, or genetic map, despite the fact that there was very little genetic material left to work with (less than 0.1 percent). What they discovered was that the leprosy bacteria was similar to modern strains of the disease, which are not nearly as contagious among humans. That led the scientists to conclude that the human population adapted natural defenses against the disease relatively quickly. The results were published today in the journal Science, and may lead to better disease tracking and fighting tools. Leprosy still affects more than 200,000 people annually, scientists noted.