Canine Protothecosis; Ocular Findings, Diagnosis, Treatment and Outcome in 8 Dogs

To describe the clinical signs, diagnostic methods, treatment, and prognosis of Prototheca spp. infection in canine species with special interest in ocular manifestations.

Information extracted from the medical records of six veterinary practices between 2017 and 2022: Palma, Barcelona, Valencia, Murcia, and A Coruña (Spain), and Bern (Switzerland) was reviewed to identify ocular protothecosis. All the relevant data for each patient diagnosed with the disease were compiled for the study.

A total of eight dogs were included: six from Spain and two from Switzerland. Three were purebred dogs, two were mixed-breed Collies, and three were crossbreeds. The median age was 4.5 years. Five of the eight dogs exhibited chronic diarrhea prior to ophthalmological signs. All of the dogs exhibited blindness. Highly cellular subretinal fluid resulting in retinal detachment was present in all cases. Successful diagnostic methods included rectal scraping, cytology of the subretinal fluid, footpad biopsy, globe histopathology and intestinal biopsy. Treatment was oral itraconazole in all dogs combined with subcutaneous amphotericin B in one. The average survival time was 77 days after the first consultation. One patient, bilaterally enucleated, is alive 2 years after the diagnosis.

Rectal and vitreal-subretinal cytology being the primary diagnostic methods. Prototheca spp. should be considered as a differential diagnosis in dogs with chronic diarrhea. Panuveitis and high cellular retinal detachment are characteristic. To the best of the authors' knowledge, this is the first multicenter retrospective study in Europe focusing on the ophthalmic presentation of Prototheca spp. infection in dogs.