Leprosy has been feared for the entirety of the history. I know it is curable nowadays, but I have a question about the "natural" course of the disease.

I remember reading a claim that Old World populations built genetic resistance to leprosy within the historic time - that even a 1000 years ago leprosy was more dangerous than it would have been today even if the drugs treating it disappeared. Does it have any basis? Alternatively is it possible that bacteria itself became less damaging like it happens with other infections sometimes? Or it is completely baseless and 2000 years ago it has been no more virulent than it is nowadays?