From time to time plagues such as bubonic plague, caused mainly by rat fleas (Xenopsylla cheopis, a parasite found on brown rats), "red" dysentery and other scourges killed a great deal of Flensburg's population. Lepers were strictly isolated, namely at the St.-Jürgen-Hospital ("Helligåndshospital", built before 1290), which lay far outside the town's gates, where the St. Jürgen Church is nowadays. About 1500, syphilis also appeared. The church hospital "Zum Heiligen Geist" ("To the Holy Ghost") stood in Große Straße, now Flensburg's pedestrian precinct.