Chaetomiaceae Fungi, Novel Pathogens of Equine Neurotropic Phaeohyphomycosis.
Authors: Plumlee Quinci, Meason-Smith Courtney, Dieterly Alexandra, Gomez Gabriel, Porter Brian F, Rodrigues Hoffmann Aline
Journal: Veterinary pathology
Summary
# Chaetomiaceae Fungi as Emerging Equine Neurotropic Pathogens Chaetomiaceae fungi, a group of dematiaceous organisms previously documented only as rare human pathogens, have now been identified as causative agents of mycotic encephalitis in horses, prompting re-evaluation of differential diagnoses in equine neurological disease. Researchers examined seven cases of hyphal mycotic encephalitis using histopathology alongside molecular diagnostic techniques—specifically panfungal PCR targeting ribosomal RNA and internal transcribed spacer-2 regions—to identify and characterise the fungal organisms present in affected brain tissue. Four cases revealed >98% sequence homology with Chaetomiaceae species (Acrophialophora fusispora, Acrophialophora levis, and Chaetomium strumarium), whilst affected horses ranged from 8 to 22 years old and presented with neurological signs; macroscopic findings included multifocal cerebral haemorrhage, thalamic swelling with discolouration, and malacia, with microscopic lesions dominated by focal necrosis, vasculitis, and granulomatous inflammation harbouring characteristic 7–10 μm wide, septate, non-pigmented hyphae with dichotomous branching. For equine practitioners, this represents the first documented evidence that Chaetomiaceae should be considered when investigating chronic or progressive neurological presentations, particularly where conventional diagnostics prove inconclusive, and suggests that molecular fungal identification may be essential for confirming diagnosis in suspected mycotic encephalitis cases.
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Practical Takeaways
- •Chaetomiaceae fungi should be considered as differential diagnosis in horses presenting with unexplained neurologic signs and encephalitis, particularly in cases unresponsive to standard treatments.
- •Molecular diagnostics (panfungal PCR) are essential for definitive identification of emerging fungal pathogens; histopathology alone cannot distinguish this family reliably.
- •Prognosis appears grave given the CNS involvement and nature of infection; focus should be on recognition to guide necropsy findings and potentially identify environmental sources.
Key Findings
- •Seven horses aged 8-22 years presented with neurologic signs caused by Chaetomiaceae fungi, a previously unreported pathogen in equine species.
- •Molecular analysis identified causative organisms as Acrophialophora fusispora, Acrophialophora levis, and Chaetomium strumarium with >98% genomic homology.
- •Histopathologic hallmarks included multifocal necrosis, neutrophilic to granulomatous inflammation, vasculitis, and 7-10 μm septate parallel-walled fungal hyphae in brain tissue.
- •Macroscopic lesions featured multifocal hemorrhage, thalamic swelling with red-yellow discoloration, and focal cerebral malacia affecting cerebrum, thalamus, and brainstem.