the worgen curse in gilneas came from arugal if i recall correctly
arugal was a kirin tor mage who was expelled from dalaran for researching that shit, he went west to silverpine forest and made shadowfang keep his home where he continued his research. eventually he made contact with the worgen in the emerald dream and brought some of them to azeroth, soon afterwards they started to proliferate beyond the keep and started infesting the wider area. initially they didn't make it into gilneas because it was walled off by the greymane wall.
years later, during cataclysm, the gilneans were facing a full scale assault from sylvanas' forsaken. they found out that the worgen curse had the side effect of making you immune to the plague of undeath and prevented your dead body from being resurrected, so they willingly took the curse on themselves, hoping that it would give them an edge in the fight against sylvanas. that's how they ended up as a nation of furries.