(thanks to irreligion.org for the Leviticus reference).
The cleansing ritual is necessary to "make atonement for him that is to be cleansed because of his uncleanness". I wonder how many religious doctors, guided by the bible or its even wackier interpretations such as Christian Science, see their patients' illnesses as consequence of sin.
Cleansing ritual from leprosy:
Get two birds. Kill one. Dip the live bird in the blood of the dead one. Sprinkle the blood on the leper seven times, and then let the blood-soaked bird fly away. Next find a lamb and kill it. Wipe some of its blood on the patient’s right ear, thumb, and big toe. Sprinkle seven times with oil and wipe some of the oil on his right ear, thumb and big toe. Repeat. Finally find another pair of birds. Kill one and dip the live bird in the dead bird’s blood. Wipe some blood on the patient’s right ear, thumb, and big toe. Sprinkle the house with blood 7 times.
– Leviticus 14:2-52