Immunotherapy for treatment of multicentric cutaneous pythiosis in a dog

A 4-year-old Labrador Retriever was referred for evaluation of 2 ulcerative nodular cutaneous lesions. One lesion was located on the medial aspect of the right carpus; the other was located on the medial aspect of the left tarsus. The dog had spent its entire life in the southeastern part of the United States and approximately half of its time outdoors with free access to a nearby lake. Histologic examination of full-thickness wedge biopsy specimens from both lesions revealed severe, multifocal, puruloeosinophilic to pyogranulomatous deep dermatitis with intralesional filamentous structures, fibroplasia, and neovascularization. Examination of sections stained with Gomori methenamine silver stain revealed a moderate number of wide, bulbous, irregularly septate, branching hyphae. Results of an immunodiffusion test and an ELISA for anti-Pythium insidiosum antibodies were positive. Amputation was eliminated as a treatment option because lesions involved 2 limbs. Long-term systemic antifungal treatment was also rejected because of the cost, lack of therapeutic effect in many cases, and potential for adverse effects. The dog was treated with 2 doses of an anti-P insidiosum vaccine administered 2 weeks apart. One month later, the lesions were nearly completely healed, and values obtained via the immunodiffusion test and ELISA had decreased. Results of the immunodiffusion test and ELISA were negative 1 year later, and the dog had not had any recurrences.