Protothecal colitis in a German shepherd dog.

A 3 1/2-year-old intact male German Shepherd Dog was admitted with a history of protracted haemorrhagic diarrhoea and tenesmus. Clinical evaluation revealed thickening of the rectal mucosa and presence of fresh blood and mucus in the faeces. Severe mucosal granularity and multiple nodules, in addition to a rectal stricture 7 to 9 cm from the anus, were found on colonoscopy. Histopathological evaluation of biopsy specimens identified organisms with morphologic features compatible with those reported for Prototheca spp. Although surgical excision of the rectal stricture was performed and ketoconazole treatment was instituted postoperatively, the dog's clinical condition deteriorated and euthanasia was performed 4 months later.