Molecular identification of fungal pathogens in nodular skin lesions of cats

Abstract

In a retrospective study, we investigated 52 formalin-fixed, paraffin-embedded (FFPE) samples from cats with histologically confirmed cutaneous and subcutaneous mycoses to determine if the pathogens could be identified by molecular methods. Aim of the study was to obtain a deep understanding of the spectrum of infectious agents, which, as we hypothesized, was not available by histopathology alone. Detection of feline and fungal DNA was achieved in 92.3% and 94.2% of the samples, respectively. Most of the subcutaneous infections in cats were caused by Alternaria spp. (63.5%), followed by Cryptococcus neoformans (7.7%), Histoplasma capsulatum (5.8%), Sporothrix spp. (3.8%), Aspergillus vitricola, Aureobasidium pullulans, Exophiala attenuata, Fusarium oxysporum, Lecythophora cateniformis, Microsporum canis, and Phialophora sp. (1.9% each). The results from molecular identification indicate that correct identifications of the fungal pathogens by histology alone were rarely possible. The spectrum of fungal pathogens identified after DNA extraction from FFPE samples was much broader than that expected by classical histopathology. This was especially noted in alternariosis in that the micromorphological pattern in tissue was misleading and could be confused with that of cryptococcosis. Due to different susceptibilities to antifungal agents, it is important to arrive at a definitive diagnosis, which might be possible by examination of the fungus recovered in culture and/or molecular methods, in addition to the histopathologic techniques.

Diagnosis and treatment of dermatophytosis in dogs and cats.

“…There were 100% concordant results between PCR and culture. The use of PCR to diagnose infectious agents in nodular lesions in cats again confirmed the usefulness of PCR, given that this can rarely be done via histological examination alone . There are two published studies evaluating PCR‐based methodology for the diagnosis of dermatophytosis from cat or dog hair .…”

Phaeohyphomycoses, Emerging Opportunistic Diseases in Animals

“…These findings indicate that alternariosis is by far the most common nodular fungal skin disease of cats in the United Kingdom. A recent investigation by Bernhardt et al indicated that the same situation probably occurs in cats in Germany (94). In a study by Chermette et al, Exophiala attenuata was also reported as the agent of nasal granuloma in a cat (95).…”

Opportunistic Invasive Cutaneous Fungal Infections Associated with Administration of Cyclosporine to Dogs with Immune‐mediated Disease

“…In particular, there was a lack of definitive identification of fungi to species level and only 5/15 (33%) of our dogs with OIFIs had biopsies of the skin lesions. Molecular identification techniques are becoming more widely available for identification of veterinary isolates; however, these techniques were not as widely available at the time of diagnosis in this retrospective report. Also, while broad range PCR can detect rare and unreported pathogens, PCR tests are susceptible to contamination during sampling, handling or storage of specimens, making this a potential drawback as this would increase false positives .…”