Touch wood, never had the full blown YBS; if I see a yb holding corn, or one has thrown their nights meal up, all I do is, the next day put a spoonfull of bleach in the water; it just disinfects it so the problem isnt passed round. Then its up to the yb itself to sort it out, I think its better if they overcome it themselves, but by the next night doing that they are usually back on, if not they get removed from the team.