Concise Bible Dictionary:

This loathsome and incurable disease is often mentioned in scripture. Some persons were smitten with leprosy as a direct judgment from God, as were Miriam (though she in grace was subsequently cured), Gehazi, and Amaziah; in the case of Gehazi the disease was to descend also to his seed. God’s power alone could cure the leper, as seen in the case of Naaman the Syrian, and in the many lepers that the Lord cured when on earth. Amaziah dwelt in a separate house, and the lepers were enjoined to proclaim, their own condition by calling out, “Unclean, Unclean” (Lev. 13:4545And the leper in whom the plague is, his clothes shall be rent, and his head bare, and he shall put a covering upon his upper lip, and shall cry, Unclean, unclean. (Leviticus 13:45)).
Leprosy is a vivid type of sin, and its insidious working, producing an unclean condition. Leviticus 13-14 treats of the way it was to be discovered and dealt with by the priests as those having the mind of God. The instruction in Leviticus 13:12-1312And if a leprosy break out abroad in the skin, and the leprosy cover all the skin of him that hath the plague from his head even to his foot, wheresoever the priest looketh; 13Then the priest shall consider: and, behold, if the leprosy have covered all his flesh, he shall pronounce him clean that hath the plague: it is all turned white: he is clean. (Leviticus 13:12‑13), though seemingly paradoxical, is significant: when the leprosy covered all the skin, the priest was to pronounce the man clean: “it is all turned white: he is clean.” That is, the leprosy, instead of striking inwards, had worked itself out, typical of a man truly confessing his sin; then the effect only of the defilement remains.
Besides leprosy in the person, laws were also given as to leprosy in a garment, answering to the sin that may be in a person’s surroundings, which must be cleansed or destroyed. There is also leprosy in the house (when they were come into the land), answering to manifest sin in a Christian assembly, which must be removed, or the assembly must be dissolved. Holiness becomes God’s house.
Spinalonga – Leprosy Island (Crete, Greece)
Two Cases of Leprosy – April 2, 1920 (Dominican Republic)