I'm looking into various aspects of the bible and its claimed divine inspiration, and am in the process of studying the passage in Leviticus which deals with what has been translated as "leprosy" as it often cited as an example of hygiene guidance before knowledge of germs was widely available.
Whilst I haven't finished yet, I'm leaning towards the conclusion that the ostracism of "lepers" wasn't particularly effective in preventing a spreading of the disease, but was mainly intended to keep what was viewed as ritually "unclean" (and perhaps what was brought about by God as punishment) separate from what was "clean".
12 And if the leprous disease breaks out in the skin, so that the leprous disease covers all the skin of the diseased person from head to foot, so far as the priest can see, 13 then the priest shall look, and if the leprous disease has covered all his body, he shall pronounce him clean of the disease; it has all turned white, and he is clean. 14 But when raw flesh appears on him, he shall be unclean. 15 And the priest shall examine the raw flesh and pronounce him unclean. Raw flesh is unclean, for it is a leprous disease. 16 But if the raw flesh recovers and turns white again, then he shall come to the priest, 17 and the priest shall examine him, and if the disease has turned white, then the priest shall pronounce the diseased person clean; he is clean.
Here's what The Oxford Companion to the Bible has to say on this point (part of the entry by George Wesley Buchanan, "Leprosy"):
Those who had been diagnosed as lepers by the priest were required to separate themselves from the community. This was not for medical but religious reasons. Biblical lepers were treated not as ill but as ritually unclean. The priest had no technique for healing lepers; he only determined whether or not they had been healed ("cleansed"). When he considered the affliction healed, he then offered the correct sin and guilt offerings so that the former leper might be atoned for this impurity.
Lepers had two colours of skin, which was taboo, as was plowing with two kinds of beasts, raising two kinds of grain in one field, weaving two kinds of thread into one piece of cloth, or cross-breeding two kinds of cattle (Leviticus 19:19; Deuteronomy 22:10,11). Those covered completely with the disease, so that they had only one colour of skin, were allowed to return to the community, because they were no longer lepers. Once they began to heal, however, they were classified as lepers and were isolated again.
I'm particulary interested in whether we know of any diseases which would have come under these laws and ceases to become infectious when spread all over a person's body or not? Is such a thing possible? (I haven't found anything yet.)