True, but the leprosy of Leviticus was not the modern disease we call leprosy, which has different symptoms.
How do these symptoms differ? As was pointed out above, washing in the Nile may have preserved health better than having very little water in more desert areas. ONe reason for the success of Islam was the rule about washing hands 5 times a day before prayer. Also the rule about using the right hand for eating from the communal cookpot, and the left hand for cleaning human waste.