Parashas Metzora · Passuk 15:04
Chabad.org — English translation + Rashi
Torah Temima points to Toras Kohanim.
English: “The zav” — the zav [alone], and not a baal keri, nor a stone afflicted with nega, nor one impure from a corpse, nor a corpse, convey midras impurity of bed and seat.
Restriction of midras to the zav
Chazal limit the severe midras impurity of mishkav/moshav to the zav (and parallel categories such as niddah/zavah), not to other impurities.