Cutaneous protothecosis in a dog.

A dog was infected systemically with Prototheca wickerhamii but showed only cutaneous protothecosis. The lesions appeared progressively and consisted of non-pruritic scrotal swelling and ulceration, cutaneous nodules, crusty ulcerative lesions over the trunk and serous rhinitis. The diagnosis was based on skin biopsy findings and specific culture. Microscopic examination revealed a diffuse pyogranulomatous dermatitis and numerous protothecal organisms of different sizes within the cytoplasm of phagocytic cells. Treatment with oral ketoconazole for six months resolved all the clinical signs except the scrotal granuloma which, although it was significantly reduced, had to be removed surgically. However, after five months the condition returned.