“Guard against an outbreak of leprous skin disease by being very careful. You shall carefully observe whatever the Levitical priests instruct you, just as I have commanded them. Remember what Yahweh your God did to Miriam on your journey out of Egypt.”
They were really afraid of leprosy. This is like Leviticus, chapters 13-14, and Numbers, chapter 12. There is the reminder of what happened to Miriam. The Levite was the priest, the doctor, and the judge on leprosy.