Rhinosporidiosis is a chronic granulomatous mycotic disease of the mucocutaneous tissues caused by Rhinosporidium seeberi.
This fungus, which is normally present in decaying vegetable matter, stagnant water or dust presumably serves as the source of infection, and local trauma to the nasal mucosa seems to predispose to disease.
Rhinosporidium normally resides within crypts of turbinate epithelium and are slow growing, causing localized proliferation of granulation tissue. This granulomatous response results in polyps, tumors or papillomas primarily affecting the mucous membranes of the nostrils or ocular conjunctivae. These growths are friable, highly vascularized and hyperplastic and tend to bleed following severe sneezing or facial rubbing.
Multiple host-specific strains have been identified, implying cross-species transmission between humans, cattle, dogs and other mammals.
Clinically affected dogs usually present with chronic episodic sneezing and nasal discharge. Severe cases may result in epistaxis and blood nasal discharge.
On rhinoscopy, granulomatous masses may be visible on the nasal turbinates. Impression smears and histopathology usually reveal lymphoplasmacytic and neutrophilic inflammation with spores typical of Rhinosporidium.
Diagnosis is based on cytological evidence of 5- to 10-μm endospores and 50- to 1,000 μm sporangia, with definitive diagnosis confirmed by dotELISA or PCR assaying.
In non-responsive cases, a rhinotomy may be performed and a topical clotrimazole or povidone-iodine dressing is placed as a 'tie-over' dressing, replaced every 2 - 3 days until all exposed tissue is covered by healthy granulation tissue.
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