This quest is not available in game.
Apothecary Johaan in the town of Brill wants you to collect 5 Vials of Darkhound Blood.
- Darkhound Blood × 5
Lady Sylvanas has called upon the Royal Apothecary Society. The Dark Lady believes our knowledge coupled with the newfound magic will provide the key to Arthas's demise. She has challenged us to concoct a new plague, a plague deadlier than any ailment on Azeroth. This new disease will bring Arthas's Scourge Army to ruin.
My studies show that the blood of beasts might prove to be the key. Bring to me 5 vials of darkhound blood so I can test my theory.