Mycotic Rhinitis and Sinusitis in Florida Horses.
Authors: More Sunil Nivrutti, Hernandez Oscar, Castleman William L
Journal: Veterinary pathology
Summary
# Editorial Summary: Mycotic Rhinitis and Sinusitis in Florida Horses Upper airway fungal infections in horses represent a significant diagnostic challenge, particularly in subtropical and tropical climates where environmental conditions favour fungal proliferation. Researchers examined 52 nasal and sinus biopsy samples from affected horses across Florida using combined histopathology, panfungal polymerase chain reaction (PCR), and DNA sequencing to characterise the causative agents and their pathological presentations. Zygomycosis and pythiosis accounted for 31 cases, whilst phaeohyphomycosis (darkly pigmented fungal infections) comprised 18 cases, with eight additional cases caused by less common fungi including Flavodon flavus, Curvularia lunata, and Toxicocladosporium irritans—several reported in equine tissues for the first time. Molecular techniques proved markedly more sensitive for phaeohyphomycosis (39% identification rate) and non-pigmented infections (100% identification rate) than for zygomycosis (3% identification rate), suggesting that histomorphology remains critical for diagnosing the latter group despite modern molecular tools. Clinicians managing horses with chronic nasal discharge, upper airway obstruction, and abnormal respiratory noise should maintain high suspicion for mycotic infection in endemic regions; definitive diagnosis requires biopsy and histochemical assessment, with PCR and sequencing particularly valuable for confirming phaeohyphomycosis when morphological features are atypical.
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Practical Takeaways
- •Suspect fungal rhinitis/sinusitis in Florida horses presenting with upper airway obstruction and nasal discharge; zygomycosis and phaeohyphomycosis are the most likely culprits requiring histopathology for diagnosis
- •Morphologic assessment combined with PCR/DNA sequencing provides the most reliable identification of fungal pathogens, particularly for phaeohyphomycosis cases
- •Be aware that multiple fungal species beyond common pathogens can cause rhinitis/sinusitis in subtropical/tropical climates, necessitating thorough diagnostic investigation
Key Findings
- •Zygomycosis/pythiosis (31/52 cases, 60%) and phaeohyphomycosis (16/52 cases, 31%) were the most common fungal causes of rhinitis/sinusitis in Florida horses
- •PCR and DNA sequencing identified fungal pathogens in 11/52 cases (21%), with highest success in phaeohyphomycosis (39%) and other nonpigmented fungi (100%)
- •Eight previously unrecognized fungal species were identified as causes of equine rhinitis/sinusitis, including Flavodon flavus, Curvularia lunata, and Toxicocladosporium irritans
- •Clinical signs included upper airway obstruction, abnormal respiratory noise, and nasal discharge associated with granulomatous, pyogranulomatous, and fibrinopurulent lesions