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Fungal Disease - Rhinosporidiosis

Etiology

Rhinosporidium seberi is a fungal organism. Attempts to culture it using conventional fungal culture media were unsuccessful; however, the organism has been grown in tissue culture.

Disease prevalence

The disease is endemic in India and Argentina but North American reports have come almost exclusively from the southern United States.

It is thought that infection is acquired by mucosal contact with stagnant water or dust and that trauma is a predisposing factor.

Clinical Findings

The disease appears to be rare, and it is reported only in dogs.

There appears to be a predilection for large-breed, male dogs.

Affected dogs typically present for wheezing, sneezing, unilateral sero purulent nasal discharge, and epistaxis.

Nasal polyps may be in size from a few millimeters up to 3 cm are pink, red, or grayish and are covered with numerous pinpoint, white foci (fungal sporangia).

Polyps may be sessile or pedunculated, and they may protrude out of, or involve, the mucocutaneous area of the nostril.

Differential diagnosis

It includes numerous infectious granulomas and neoplasms.

Diagnosis

Cytologic examination of nasal exudates or histologic examination of the polyp should be diagnostic.

Biopsy findings include a fibro vascular polyp containing numerous sporangia (spherules) having a thick, double outer membrane.

The sporangia vary from 100 to 400 µm in diameter and contain a variable number of sporangiospores (endospores).

A variable number of lymphocytes, plasma cells, and neutrophils are often found where sporangiospores (2 to 10 µm in diameter) have been released into the surrounding connective tissue.

Clinical Management

Surgical excision is the treatment of choice, although recurrence 6 to 12 months after surgery has been reported.

Successes have been reported with dapsone or ketoconazole administered orally; however, the utility of medical therapy in canine rhinosporidiosis requires further evaluation.


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