 BPV-4 causes squamous cell carcinomas of the alimentary tract, and BPV-1/2 causes carcinomas and haemangioendotheliomas of the urinary bladder, in both cases in animals that have fed on bracken ("Pteridium aquilinum").Such cancers are common in locations where grazing land is infested with bracken, such as the western Scottish Highlands, southern Italy and the Nasampolai Valley in Kenya.Bracken contains several immunosuppressants and mutagens, including quercetin and ptaquiloside.