Prototheca spp

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Numerous small granulomas of the myocardium from a dog with disseminated protothecosis[1]
Paw of a dog with draining ulcers associated with cutaneous protothecosis

Prototheca spp are a ubiquitous saprophytic achlorophyllus algae which sometimes cause disseminated disease (protothecosis) in dogs across Europe, Asia, Africa, Oceania, and in North America[2].

In dogs, infections are usually associated with immunosuppressed states, or from injuries to the skin.

Species which are pathogenic to dogs include:

  • Prototheca wickerhamii
  • Prototheca zopfii[3]
  • Auxenochorella species[4] (genetically related to Prototheca)

The organism is ubiquitous in nature and is commonly found in sewage, slime flux of trees and in animal wastes. Despite the abundance of this organism in nature, the incidence of disease is rare.

Clinically affected dogs present with either cutaneous or disseminated systemic infection.

The systemic form of protothecosis is most often caused by P. zopfii. Clinical signs are usually characterized by chronic hemorrhagic diarrhoea[5] and granulomatous meningoencephalitis[6][7]. Retinal damage is quite common.

Cutaneous infection, which are more rare, are associated with infection by P. wickerhamii. Skin lesions consist of nodules and draining ulcers with crusty exudates on the extremities, trunk and mucosal surfaces. Hyperkeratosis may be present as well as secondary bacterial infections.

Diagnosis is based on clinical symptoms as well as microscopic examination and culture of urine, CSF, rectal scrapings, aspirates or biopsies of eyes, histology of colonic biopsies as well as skin and lymph nodes.

Definitive diagnosis requires isolation and culture of the organism[8], often requiring histological analysis of postmortem brain samples and PCR assay analysis[9].

Treatment is difficult in most cases due to the disseminating nature of algal growth in vivo.

Combination therapy with amphotericin B and itraconazole have been successful[10]. Additional drugs include tetracycline, ketoconazole, fluconazole and clorimazole have been used to attempt to treat this disease[11].

Surgical debulking may assist clinical resolution of symptoms.


  1. Lane LV et al (2012) Disseminated protothecosis diagnosed by evaluation of CSF in a dog. Vet Clin Pathol 41(1):147-152
  2. Hollingsworth SR (2000) Canine protothecosis. Vet Clin N Am Small Anim Pract 30:1091-1101
  3. Rizzi TE et al (2006) More than meets the eye: subretinal aspirate from an acutely blind dog. Vet Clin Pathol 35(1):111-113
  4. Tsuji H et al (2006) An isolate of Prototheca wickerhamii from systemic canine protothecosis. Vet Microbiol 118(3-4):305-311
  5. Sapierzyński R & Jaworska O (2008) Protothecosis as a cause of chronic diarrhoea in a dog. Pol J Vet Sci 11(3):225-229
  6. Salvadori C et al (2008) Protothecal granulomatous meningoencephalitis in a dog. J Small Anim Pract 49(10):531-535
  7. Ribeiro MG et al (2009) Phenotypic and genotypic characterization of Prototheca zopfii in a dog with enteric signs. Res Vet Sci 87(3):479-481
  8. Rallis TS, et al (2002) Protothecal colitis in a German Shepherd Dog. Aust Vet J 80:406-408
  9. Ahrholdt J et al (2012) Epidemiological analysis of worldwide bovine, canine and human clinical Prototheca isolates by PCR genotyping and MALDI-TOF mass spectrometry proteomic phenotyping. Med Mycol 50(3):234-243
  10. Stenner VJ et al (2007) Protothecosis in 17 Australian dogs and a review of the canine literature. Med Mycol 45(3):249-266
  11. Gupta A et al (2011) What is your diagnosis? Cerebrospinal fluid from a dog. Eosinophilic pleocytosis due to protothecosis. Vet Clin Pathol 40(1):105-106