Although Prototheca species are ubiquitous in nature, they rarely cause systemic disease in animals or people.39 People with systemic protothecal infections are almost always immunocompromised.4,39 Suggested predisposing causes in people include neoplasia, human immunodeficiency virus infection, immunosuppressive drug
use, systemic fungal infections, and deficiencies in cell-mediated immunity.4,39-41 Immunosuppression may not be apparent clinically, and protothecosis has been reported in a person who had no concurrent
disease and exhibited immunocompetence based on all test results.42 This patient had elevated antibodies to the organism and responded to antifungal therapy; an underlying cause for the patient's
infection was not established.
In dogs, the systemic disease is more common than it is in people, but the reason for this is unknown. In most reported cases
in dogs, underlying immunosuppression was not found,2,6,11,13,19,24,26,31,32 but few of these patients have undergone immune status assessment.8 A case has been reported in which a dog with protothecosis had deficits in both T-lymphocyte and polymorphonuclear activity.21 Although our patient's immune system status was not specifically assessed, the dog may have been immunocompromised. The
presence of neoplasia in people has been documented as a predisposing cause for protothecosis,41 and this dog had confirmed adrenal and hepatic tumors. The dog's previous major abdominal surgery could also have led to
immunosuppression. Because the dog began receiving glucocorticoids after its ocular signs developed, it appears that the dog
did not acquire the infection because it was pharmacologically immunosuppressed. But it is possible that this therapy may
have allowed the infection to further disseminate.
Consider systemic protothecosis in your list of differential diagnoses for ocular inflammatory diseases, especially when severe
chorioretinitis is present. Affected patients may present with ocular signs (especially blindness) alone or in conjunction
with signs of gastrointestinal, neurologic, or renal disease. Diagnosing protothecosis may be difficult, but aspirating the
subretinal fluid of dogs with retinal detachments will often yield Prototheca organisms.
At this time, protothecosis is minimally treatable and the prognosis is grave because the organism has usually disseminated
throughout the body before it is detected. In the future, treatments directed at strengthening a patient's immune response
and earlier detection methods may improve the outcome in patients with protothecosis.
Juliet R. Gionfriddo, DVM, MS, DACVO
Department of Clinical Sciences
College of Veterinary Medicine
Colorado State University
Fort Collins, CO 80523
1. Kruger W. Kurz charactistic einger niedern Organismen in Laftflusse de laublaume. I. Ueber einen neuen Pilz-typus, reprasentiert
durch die Gattung Prototheca (Pr. moriformies et Pr. zopfii). II. Ueber zwei aus Laftflussesrein gezuchtet Algen. Hewigia 1894;33:241-266.
2. Van Kruiningen HJ, Garner FM, Schiefer B. Protothecosis in a dog. Pathol Vet 1969;6:348-354.
3. Migaki G, Font RL, Sauer RM, et al. Canine protothecosis: review of the literature and report of an additional case. J Am Vet Med Assoc 1982;181:794-797.
4. Pressler BM, Gookin JL, Sykes JE, et al. Urinary tract manifestations of protothecosis in dogs. J Vet Intern Med 2005;19:115-119.
5. Sudman MS. Protothecosis. A critical review. Am J Clin Pathol 1974;61:10-19.
6. Tyler DE, Lorenz MD, Blue JL, et al. Disseminated protothecosis with central nervous system involvement in a dog. J Am Vet Med Assoc 1980;176:987-993.
7. Berkhoff HA, Connelly MR, Lockett LJ. Differential microbiological diagnosis of protothecosis from non-human sources. Am J Med Technol 1982;48:609-612.