Blizzard adds in a new instance, Zul'Gurub. Inside is the god of blood, Hakkar. Well, when you fight him he has a debuff called Corrputed Blood. It does like 250-350 damage to players and affects nearby players. The amazing thing is SOME PLAYERS have brought this disease (and it is a disease) back to the towns, outside of the instance. It starts spreading amongst the general population including npcs, who can out generate the damage. Some servers have gotten so bad that you can't go into the major cities without getting the plague (and anyone less than like level 50 nearly immediately die).

GM's even tried quarantining players in certain areas, but the players kept escaping the quarantine and infect other players.