Either the Swamp Fever has already been toned down, or it's not as terrible.
I got it yesterday by thoroughly scouring ~15 map tiles of local swamp for candleberries -- it wasn't a "brief" exposure by any means. It was at 1 when I logged out.
5 hours ago I logged in to find it at 36. It has been ticking down gradually since then, now at 23.
NOTE: putting the character into a bed pushed it up, to 38 within 10 minutes. So instead I was mostly idling in fresh air since then. No idea if that's related, but the wound didn't tick up anymore. I never applied any snake juice.
EDIT: now at 21 (5 minutes later).