Infection with Mycobacterium leprae causes a chronic, disfiguring skin disease called leprosy. It’s characterized by progressively worsening skin lesions that cause nerve and tissue destruction. The bacteria grow best on cooler areas of the body, so lesions (called granulomas) tend to develop on the limbs and face. Leprosy is spread by prolonged contact with someone infected, and also by nasal droplet (from breathing, sneezing, coughing). Before antibiotics, there was no cure for leprosy, although many remedies were attempted, including bathing in blood, applying snake venom, repeated bee stings, castration, and oil from chaulmoogra trees. Because it was contagious and relatively untreatable, lepers were usually quarantined and segregated from the general population.

The Hebrew word for leprosy (tsara’ath) was a nonspecific term for any skin condition, which could also refer to mildew and mould on clothes or houses. Moses’ Law included extensive regulations for leprosy on people or their possessions. In general, anyone with an open skin lesion was considered unclean, whether it was true leprosy or something else. Lepers (those with skin lesions) had to live in isolation and shout, “Unclean! Unclean!” when around others. When a skin disorder resolved, the person had to be examined by a priest and be ceremonially cleaned. After bathing, shaving, washing one’s clothes, and offering sacrifices, the person could then officially rejoin the community. However, unlike other skin conditions, leprosy rarely self-resolved, so true lepers were typically outcasts for life.