The disease originated from Hakkar the Soulflayer -- the manager of this very initial 20-player raid Blizzard released. Hakkar would toss Corrupted Blood on wow classic gold
and it would damage them for about 10 minutes. Players would disperse the impact on others if they got too near those infected. Following the 10 seconds were done, or players finished the boss battle, the harmful impact was supposed to end. Only it did not.
A programming oversight allowed the debuff to disperse beyond the website of this Hakkar boss struggle and to the world at large. Much like rats fueled the Bubonic Plague, characters' trained animals spurred the Corrupted Blood outbreak. Hunter characters may summon and dismiss pets to fight at their side at will. Once ignored, all the consequences on the pets are paused until it is called back out again. In consequence, the critters could contract Corrupted Blood during the boss fight, disappear and then exhibit the symptoms again elsewhere in the world map when they were again summoned. There it would spread to other players and pets that came in contact with them.
Cities like the dwarven city Ironforge and buy wow gold classic
orc town Orgrimmar were overrun within hours. Non-playable personalities, who couldn't die due to particular coding, would also catch the effect, meaning any participant who passed by them could receive Corrupted Blood.