Jacob's Well is another religious manual...that currently holds the title for most disgusting story involving leprosy in Middle English.
A bishop meets a leper on a road. The leper asks the bishop to lick the bogey out of his nose as his nose is too tender to be wiped with a cloth. The bishop does lick the nose and as he does so a gem stone falls out of the leper's nose, it is the stone of grace...a gift from God for the bishop's humility...still gross though! Naturally the leper disappears having given the bishop this wonderful gift!