The beast’s head is slain, a wound that is described as “the plague of his death” ( he plege tou thanatou ; Revelation 13:3).

That might go in a couple directions. On the one hand, the Hebrew noun nega’ (plague) is used only once in the plague narratives, in Exodus 11:1, when Yahweh announces one final plague against Pharaoh. (Even in the LXX, the noun form plege is used only a few times in Exodus: 12:13; 22:1; 33:5). This plague is the Angel of Death, who kills the firstborn of Egypt. It is a plague of death, and the sea beast undergoes a Passover-like event.

On the other hand: The Hebrew word is also used regularly for the “plague” of leprosy, and this is far and away the most common use in the Hebrew Bible. 61 of the 78 uses of the word are found in Leviticus 13-14. Since the leprosy is a mark of death and since it marks the head in some OT passages, it is possible that we are to envision the beast with a plague of leprous death on his head.