Kesubos (77b) Rabbi Yoḥanan said: For what reason are there no lepers in Babylonia? Because they eat beets, drink beer, and bathe in the waters of the Euphrates, all of which are good for the body.
Vayikrah Rabbah (16:03) It is prohibited to go four cubits to the east of a leper. R. Simeon b. Lakish said: Even a hundred cubits. They did not really differ; the one who said four cubits referred to a time when there is no wind blowing, whereas the one who said not even a hundred cubits, eferred to a time when a wind is blowing. R. Meir would not eat eggs that came from an alley of lepers. R. Ammi and R. Assi would not enter a leper's alley. Resh Lakish, when he saw one of them in the city, threw stones towards him, and said: ' Go to your place, and do not defile other people,’ as R. Hiyya taught: He shall dwell alone of them, hid himself from him,
Ralbag(Vayikra 13:47) Tzara’at on these objects is caused by moisture and heat… this causes them to be damaged and destroyed… the discoloration is what you’d find in moldy places, like water near a dump, where things turn green or red.
Ralbag (Melachim 2 05:06)ואספתו מצרעתו - הצרעת תעשה מאחד רבים, כי מתגבורת החום העפושי יחלש
מאד החום הטבעי הקושר אברי בעל החי לאחד, ולכן יפלו אברי המצורע.
Ramban (Vayikra 13:47) The law of leprosy of houses applies only in the Land which is the inheritance of the Eternal. Now the reason why this law does not apply outside the Land of Israel is not because it is a duty which attaches to the ground, but the reason is because this matter of Divine indication of sins occurs only in the Chosen Land, wherein the Glorious Name dwells. And in the Torath Kohanim the Sages further interpreted that a house does not contract impurity until after the conquest and division of the Land by Israel, and until after each and every individual clearly knows his portion. The reason for this law is that only then do they have the ease of mind to know the Eternal, and the Divine Glory dwells among them. I think similarly with reference to the law of leprosy in garments, that it applies only in the Land of Israel, it being unnecessary to exclude the application of this law in places outside the Land, since they never occur there. For this reason also the law of leprosy in garments applies only to white garments, not to colored ones, because the color might perhaps have extracted this unclean phenomenon n that place in the garment in a natural way, and it will then not be regarded as a finger of G-d. Therefore garments colored by Heaven can contract impurity, according to the words of Rabbi Shimon. And by way of the simple meaning of Scripture, the reason why it repeats in every verse the expression “the garment, or the skin, or the wrap and the woof,” is because the matter is miraculous.
Ramban (Vayikra 13:47)AND WHEN THE PLAGUE OF LEPROSY IS IN A GARMENT. This is not in the natural order of things, nor does it ever happen in the world [outside Israel], and similarly leprosy of houses is not a natural phenomenon. But when Israel is wholly devoted to G-d, then His spirit is upon them always, to maintain their bodies, clothes and houses in a good appearance. Thus as soon as one of them commits a sin or transgression, a deformity appears in his flesh, or on his garment, or in his house, revealing that G-d has turned aside from him…
Moreh Nevuchim (03:47) Tzaraas is a miracle received in our nation by tradition, in the same manner as the effect of the trial of a faithless wife. The good effect of this belief is evident. Leprosy is besides a contagious disease, and people almost naturally abhor it, and keep away from it.
Birkat Asher on Torah, Leviticus (13:01)והנה על דעת רמב"ם והסוברים כמותו יש לשאול מדברי הגמרא (כתובות עז ע"ב): "אמר רבי יוחנן, מפני מה אין מצורעין בבבל? מפני שאוכלין תרדין ושותין שכר ורוחצין במי פרת". הרי לך שהצרעת היא עניין פיזיולוגי. ואילו על הדעה שמדובר בתופעה טבעית יש לשאול מדברי חז"ל בויקרא רבה (יז, ו) לעניין נגעי בתים: תני רבי שמעון בר יוחאי: כיון ששמעו כנענים שישראל באים עליהם, עמדו והטמינו ממונם בבתים ובשדות. אמר הקדוש ב"ה: אני הבטחתי לאבותיהם שאני מכניס את בניהם לארץ מלאה כל טוב, שנאמר: "ובתים מלאים כל טוב" (דברים ו, יא). מה הקב"ה עושה? מגרה נגעים בביתו, והוא סותרו ומצא בו סימא (אוצר). ע"כ. יוצא שאין דעת חז"ל הומוגנית, אלא מר כדאית ליה ומר כדאית ליה.
