Blood of retired adventurer (Kemsa), held in backpack, as well as in pools on ground nearby; cannot become vampire from Kemsa's blood, but can become vampire from blood of NPC vampire (Liwa), also in backpack. Only drinking Liwa's blood causes Hunger to disappear and blood sense markers to appear.

While I'm uploading this: Another reproducible problem in the same save is that trying to walk out through the town quickly results in the error message

Dwarf Fortress.exe
Dwarf Fortress.exe has stopped working
A problem caused the program to stop working correctly.
Windows will close the program and notify you if a solution is available.

(I got as far as the keep by quick travelling to the entrance, then moving to the keep one step at a time with pauses in between, though I don't know if that made a difference. I'm not sure whether this is related to my retired adventurer being the lord of that town--also, all the shopkeepers seem to have vanished from that town and the population had dropped by about a thousand (from ~1300), but that happened before my former adventurer became lord (after killing a shopkeeper?).)