@Uilebheist The sad thing is, he'll probably attach it to racism in some way.
The reasons for the downturn of leprosy in Europe a couple of centuries ago — well before the development of penicillin — are stil debated by the sort of scientists who study this stuff, but one of the leading hypotheses is, some sort of gene allele conferring relative immunity may, after the centuries of ravage killed enough suspectible Europeans, have grown dominant enough to severely curb the bacterium's infection rate. But there's still populations around who don't seem to have such an allele — a number of them famously exploited by a certain Teresa (not her biological name) — , and many of them happen to look sufficiently different from the garden variety racist to cause immense phobia in the latter.