Panfungal Polymerase Chain Reaction for Identification of Fungal Pathogens in Formalin-Fixed Animal Tissues.
Authors: Meason-Smith Courtney, Edwards Erin E, Older Caitlin E, Branco Mackenzie, Bryan Laura K, Lawhon Sara D, Suchodolski Jan S, Gomez Gabriel, Mansell Joanne, Hoffmann Aline Rodrigues
Journal: Veterinary pathology
Summary
# Editorial Summary: Panfungal PCR for Fungal Diagnosis in Fixed Tissues Histological identification of fungal infections in animal tissues presents persistent diagnostic challenges due to overlapping morphological features, the frequent unavailability of fresh material, and lengthy culture turnaround times—problems that panfungal PCR targeting the fungal internal transcribed spacer 2 (ITS-2) region may help overcome. Meason-Smith and colleagues validated this molecular approach using 128 formalin-fixed paraffin-embedded tissue blocks from horses, dogs, cats, and cattle with confirmed cutaneous, nasal, pulmonary, and systemic fungal infections, achieving PCR amplification in 91.4% of samples and high-quality sequences in 69.5%, with genus- and species-level identification matching histopathology in 61.7% of cases. The assay proved particularly valuable when histomorphology alone was inconclusive, successfully identifying fungal organisms even when histological features were ambiguous or fungal burden was low (rare organisms detected in 11.9% of blocks). For equine practitioners, this technique offers a practical complementary diagnostic tool—particularly relevant given the prevalence of fungal conditions such as guttural pouch mycosis and dermatophyte infections—that can deliver definitive identification from archived samples without the delays inherent to conventional culture methods. Implementation in specialist pathology labs could meaningfully improve diagnostic confidence and accelerate treatment decisions, though the 69.5% sequence recovery rate suggests the assay works best as an adjunct to, rather than replacement for, traditional histopathological examination.
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Practical Takeaways
- •When fungal infection is suspected but histology is inconclusive, panfungal PCR on archived formalin-fixed tissues offers a reliable way to achieve genus- and species-level identification without culturing delays
- •This molecular approach is particularly valuable for cases with sparse fungal organisms (where histomorphology alone may be unreliable) and removes the need to maintain fresh tissue samples
- •Success rates are highest when sufficient fungal burden is present on the histologic section; consider this method as a complementary diagnostic tool alongside traditional histopathology rather than a replacement
Key Findings
- •Panfungal PCR successfully identified fungal organisms from formalin-fixed paraffin-embedded tissues in 91.4% of blocks (117/128)
- •High-quality sequences suitable for identification were obtained from 69.5% of samples (89/128)
- •PCR identification matched histologic diagnosis in 61.7% of cases (79/128) and provided species-level identification where histopathology was inconclusive
- •The assay demonstrated utility across multiple tissue types (cutaneous, nasal, pulmonary, systemic) and species (canine, feline, equine, bovine)