Disseminated protothecosis in a dog coinfected with Hepatozoon canis and Ehrlichia canis.

Protothecosis is a severe, emerging opportunistic infection caused by the saprophytic, achlorophyllous microalgae of the genus Prototheca. Though uncommon, human and animal cases are increasing worldwide, making awareness of this fungal-like pathogen important in both human and veterinary medicine. We report a fatal case of disseminated protothecosis caused by P. wickherhamii in a 10-year-old, spayed, female, mixed-breed collie dog. Clinical signs included uveitis, ulcerated cutaneous nodules on the limbs and face, pododermatitis with nail loss and, lymphadenomegaly in the prescapular and popliteal lymph nodes. The cytology of enlarged lymph nodes, subcutaneous nodules, and bone marrow revealed oval yeast-like organisms, while the histopathology showed granulomatous inflammation with structures consistent with Prototheca spp. The serum chemistry panel indicated azotemia. P. wickerhamii was cultured from urine sediment and tissue smears. Co-infection with Hepatozoon canis and Ehrlichia canis was also detected. Despite rapid diagnosis following the initial consultation, the dog's condition worsened, and euthanasia was performed at the owner's request. Postmortem examination was declined. Disseminated protothecosis has a poor prognosis due to its insidious nature and the lack of effective treatments. Co-infection with hemoparasites complicated the case, contributing to the chronic progression of the disease. This case highlights the diagnostic challenges and poor outcome associated with disseminated protothecosis, particularly when complicated by other infections.