Mycotic Rhinitis and Sinusitis in Florida Horses

Rhinitis and sinusitis caused by fungal pathogens were studied in biopsy samples submitted from 52 horses distributed throughout subtropical and tropical regions of Florida. Methods included routine histopathology as well as polymerase chain reaction (PCR) with panfungal/panoomycete primers and DNA sequencing on extracted DNA (DNA barcoding). Granulomatous, pyogranulomatous, and fibrinopurulent lesions in nasal and sinus mucosa were associated with signs of upper airway obstruction and noise as well as nasal discharge. Morphologic and histochemical assessment of cases identified 31 cases of zygomycosis/pythiosis plus 1 mixed infection case, 16 cases of phaeohyphomycosis with 2 additional mixed infection cases, and 3 cases caused by other fungi. Morphologic evidence of Aspergillus sp. infection as a superficial copathogen was found in 2 of the mixed fungal infection cases. PCR and DNA sequencing facilitated identification of fungal pathogens in 11 of 52 cases (21%). No evidence of oomycete infection was found. Histomorphologic features of previously unrecognized forms of equine rhinitis/sinusitis were described, including those caused by Flavodon flavus, Curvularia lunata, Exserohilum rostrata, Alternaria alternata, Alternaria sp., Cladophialophora bantiana, Fusarium solani, and Toxicocladosporium irritans. PCR and DNA sequencing using panfungal and oomycete primers with DNA from formalin-fixed and paraffin-embedded specimens successfully identified the pathogen in phaeohyphomycosis (7/18 cases, 39%), zygomycosis/pythiosis (1/32 cases, 3%), and other nonpigmented fungal infections (3/3 cases, 100%). Zygomycosis and phaeohyphomycosis were the most common forms of fungal rhinitis found in Florida horses.