Amoebiasis was first described by Fedor A. Lösch in 1875, in northern Russia. The most dramatic incident in the US was the Chicago World's Fair outbreak in 1933, caused by contaminated drinking water. There were more than a thousand cases, with 98 deaths. It has been known since 1897 that at least one non-disease-causing species of "Entamoeba" existed ("Entamoeba coli"), but it was first formally recognized by the WHO in 1997 that "E. histolytica" was two species, despite this having first been proposed in 1925. In addition to the now-recognized "E. dispar", evidence shows there are at least two other species of "Entamoeba" that look the same in humans: "E. moshkovskii" and "Entamoeba bangladeshi". The reason these species haven't been differentiated until recently is because of the reliance on appearance.