Leprosy

In Num 12:9, Yahweh’s temper is provoked when Miriam and Aaron question Moses’s authority: וַיִּחַר אַף יְהוָה בָּם וַיֵּלַךְ, 'and the anger of Yahweh was kindled against them and he departed’. Consequently, divine ire was incited to the point that a divine malediction was produced, ṣāraʿat ["leprosy"]. Immediately thereafter, Miriam is beset with ṣāraʿat (v. 10) and, in spite of Aaron’s plea for clemency, she is temporarily removed from the camp. All of this recommends that those who are thus anathematized must be removed from Yahweh’s presence in order to assuage divine anger and prevent that wrath from expanding to others for lack of compliance. If anything, it is the concern over the spread of divine anger that makes ṣāraʿat contagious rather than any fear of a communicable disease.— Cursed Are You!, pages 342–43

<idle musing>
By the way, the other ancient Near Eastern cultures felt the same way about leprosy. That helps you understand some of the rules for leprosy doesn't it? And also why leprosy was always considered dangerous in the ancient world—it was a curse from the gods. The fact that it is contagious just made it even more dangerous. And why uncleanness was thought to spread via touch...
</idle musing>