Disseminated protothecosis caused by Prototheca bovis in two dogs

Protothecosis is an infectious disease caused by unicellular algae of the genus Prototheca, which are mainly known for causing mastitis in farm animals. However, there are reports of protothecosis in humans and other animals, such as dogs and cats, which develop cutaneous lesions or systemic lesions. Dogs with the systemic form generally develop bloody diarrhoea and blindness and neurological signs may also occur. The condition generally leads to the animal being euthanized due to the unfavourable prognosis. The objective of this work was to report two cases of disseminated protothecosis, one in a Pekingese dog (case 1) and the other in a German Shepherd Dog (case 2). Both animals had a history of chronic diarrhoea with haematochezia, which was unresponsive to various treatments in case 2. Both dogs were euthanized due to their clinical condition and were sent to the Veterinary Pathology Laboratory of the Federal University of Paraná for post-mortem examination. Macroscopically, the lesions in both cases were similar and were characterized by multifocal millimetre-sized white nodulations in the heart, skeletal muscles and intestinal serosa, as well as signs of fibrinonecrotic enterocolitis and lymphoplasmacytic interstitial nephritis. In both cases there was also retinal displacement with lymphoplasmacytic uveitis and chorioretinitis. The cytological and histopathological evaluation of the tissues revealed the presence of structures compatible with Prototheca spp. Polymerase chain reaction identified Prototheca bovis in both cases. This is a rarely reported disease and must be considered as a differential diagnosis in cases of chronic diarrhoea with haematochezia that progress to blindness in dogs.