Fake Medicine: Dracula
The symptoms of Dracula do not seem any different than someone suffering from rabies - his deadly fear of running water, sunlight. He would bite people - when he did they too would be infected with rabies. It is said he fought the Turkish army and was known as Vlad the Impaler. When he captured Turkish soldiers he force them to convert to Christianity and when they did not, he would impale the forehead to a tree. The cross was his guide but became his curse because he was bitten by some animal which was is a rabies a carrier, a dog or a fox. So when he saw the cross it reminded of the time he contracted rabies. His hate of the Turks was so much that even hated the food they ate, which had plenty of garlic in it. Dracula developed an aversion to garlic. Hence the myth grew that in order to keep Dracula away was to have garlic hanging around.
Perhaps in the days of Dracula rabies manifested in some other form, it may result in madness but not death. Dracula would stay out of light and wake up at night and go on biting people, spreading the infection. Since there was no cure all the people suffering from rabies settled in some colony, similar to a leper;s colony. Over the centuries the disease mutated and became deadly.