2 Chronicles - Chapter 26

While the reign of King Uzziah began well, his pride led to his downfall:

"But when he was strong his heart was lifted up, to his destruction, for he transgressed against the Lord his God by entering the temple of the Lord to burn incense on the altar of incense. So Azariah the priest went in after him, and with him were eighty priests of the Lord—valiant men. And they withstood King Uzziah, and said to him, “It is not for you, Uzziah, to burn incense to the Lord, but for the priests, the sons of Aaron, who are consecrated to burn incense. Get out of the sanctuary, for you have trespassed! You shall have no honor from the Lord God.” Then Uzziah became furious; and he had a censer in his hand to burn incense. And while he was angry with the priests, leprosy broke out on his forehead, before the priests in the house of the Lord, beside the incense altar. ... King Uzziah was a leper until the day of his death. He dwelt in an isolated house, because he was a leper; for he was cut off from the house of the Lord."

Leprosy is clearly linked here to sin, and in the laws of Moses we see that leprosy makes a person ceremonially unclean.

Jesus came to deal with sin and the separation from God.  The first miracle described in the Gospels is in Matthew 8 where Jesus heals a man with leprosy and says to him "Be clean".