Leprosy. As no doubt you already know, it's primarily a granulomatous disease of the peripheral nerves and mucosa of the upper respiratory tract...
Ok, no. There are two things everyone knows about leprosy:
1. It's highly contagious.
2. Your bits fall off.
Interestingly, as it turns out, neither of these facts are actually true. Whilst it used to be thought that it was highly contagious, and sufferers were banished to live out the rest of their days in leper colonies, around 95% of people are naturally immune to the disease - it's possible that in the earlier days of medicine, it was sometimes confused with syphilis, hence the fear of infectiousness. Oddly enough, you can, however, catch it from armadillos.
Leprosy doesn't cause people to lose limbs or digits, but it does affect the nerve endings and impairs peoples' ability to feel pain. This means that people with leprosy tend to injure themselves easily, not realise, and then the wounds become infected, resulting in tissue loss. Fingers and toes can also become shortened due to loss of cartilage in joints.
To this day, despite high natural immunity and the availability of effective treatments, many sufferers around the world are forced to live in leper colonies even after they've been cured, because of the fear and misconceptions surrounding the disease.