Curse of the Crimson Throne
“The vampire is perhaps the most dangerous foe the PCs face in this adventure, but if the PCs insist on attacking him, Ramoska won’t hesitate to fight back.” They weren’t kidding, he was out of your league.
Anyway, in your negotiations with him for the life of Ruan Mirukova he said he would gladly return to Ustalav. He is purely a man of science and was only working with Davaulus because he was commanded to do so by his master back in Ustalav. The disease he really wants to cure is vampirism.