I had the same problem once but I tested it before.
I wanted to feed on a young Japanese girl you'll probably meet later in the game, but before I did I saved the game to test it out. You shouldn't feed on characters you talk to ever for this reason. You won't be able to talk to them again. Hopefully after a long time he'll get back to normal, but maybe not.
It's a shame as you'll be tempted to feed on the Japanese girl with a schoolgirl outfit, but you shouldn't because you can choose to go on a mission with her. Like Arthur Kilpatrick, don't feed on him because you need to talk to him. Not that I was ever tempted to feed on that guy anyway.
