Leprosy
Leprosy is a long-known disease, dating back to 2000 BC. The disease is spread through contact with others, though most won't contract it. Still, it was once thought to be highly contagious, and as a result, those infected were usually sent to live in a secluded island where they would live out the rest of their days. This island, Spinalonga, was a leper colony from 1903 to 1957.