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
- Auxenochorella species (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 and granulomatous meningoencephalitis. 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.
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. Additional drugs include tetracycline, ketoconazole, fluconazole and clorimazole have been used to attempt to treat this disease.
Surgical debulking may assist clinical resolution of symptoms.
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