Prototheca osteomyelitis in a dog

Abstract

Canine systemic protothecosis is an uncommon disease caused by Prototheca spp., which are saprophytic algae occurring ubiquitously in nature. Infection occurs most commonly in immunocompromised animals. Most infected dogs have chronic large-bowel diarrhea, ocular lesions, neurologic deficits, or a combination thereof, but various tissues can be affected. This case highlights a unique presentation of protothecosis in a dog, in which lameness resulting from osteomyelitis was the predominant clinical sign. Key clinical message: Although osteomyelitis is an atypical manifestation, protothecosis can be a differential diagnosis for an aggressive bony lesion and is particularly worthy of consideration in immunocompromised dogs.

FIGURE 1

Radiographs of the dog’s left humerus, showing a lesion with irregular and ill-defined periosteal proliferation and cortical thickening at the level of the distal diaphysis/metaphysis. A — Mediolateral projection. B — Craniocaudal projection.

FIGURE 2

Photomicrographs of fine-needle aspirate samples obtained from the proliferative lesion of the dog’s left humerus (A) and liver parenchyma (B), both of which show numerous algal organisms consistent in appearance with Prototheca spp. In addition, a mixed leukocyte population is depicted in the left humeral lesion (A) and mildly atypical hepatocytes are shown in the liver sample (B). Modified Wright’s staining, 50× oil objective lens.

FIGURE 3

Photomicrograph of a histologic section of the dog’s liver, showing a focus of mixed inflammation with numerous algal organisms morphologically compatible with Prototheca spp. Hematoxylin and eosin staining, 30× objective lens, scale bar = 100 μm.