The role of fungi in the etiology of mass skin lesions in sables Martes zibellina L. 1758 in Tomsk region

Mass skin lesions in sables Martes zibellina in Siberia have been known since the 18th century, but their etiology is still not well understood. The disease affects up to 62 % of hunted sables, causing damage to the skin and causing serious economic loss. One of the versions suggests the participation of microscopic fungi in the occurrence of this dermatosis. In the present work, it was established for the first time that keratinophilic dermatophyte fungi of various species are involved in the etiology of skin disease in sables, some of which were discovered in the territory of the Russian Federation for the first time. The aim of the work was to reveal and identify clinically significant fungi in sables with clinical manifestations of skin diseases. Pathological material (hair, crusts) was taken from the affected areas of the skins of wild sables ( Martes zibellina L. 1758), hunted during the 2018-2019 hunting season in various areas of the Tomsk region. A total of 28 samples of pathological material were studied. Mycological examination included a Wood's lamp test, direct microscopy of the pathological material, inoculation on mycological media, followed by identification of isolated fungal cultures. Inoculation was performed on DTM-Expert, a differential diagnostic medium for dermatophytes (FNTs VIEV RAS, Russia) and on Sabouraud medium with chloramphenicol (HiMedia Laboratories Pvt. Ltd., India). The incubation was carried out under aerobic conditions at 26-28 °C, the incubation period was up to 21 days. To study the cultural and morphological features, the cultures were re-inoculated on Sabouraud agar in Petri dishes, incubated for 10-14 days. For molecular genetic identification, isolated colonies of fungi grown on Sabouraud’s medium were selected for 10 days at 26-28 °C. DNA was isolated using the GeneJET Plant Genomic DNA Purification Kit (Thermo Fisher Scientific, USA) according to the manufacturer's instructions. The resulting DNA was used to carry out the polymerase chain reaction (PCR). Regions of the internal transcribed spacer (ITS) of the ribosomal RNA gene were sequenced. Phylogenetic analysis of the obtained nucleotide sequences was performed using the SeqMan application (DNASTAR Lasergene v.7.1.0, https://www.dnastar.com/software/laser-gene/). Sequence alignment with those available in the GenBank database was performed using the Standard Nucleotide BLAST software package (http://www.ncbi.nlm.nih.gov/BLAST/). The resulting nucleotide sequences of particular interest were deposited to the GenBank NCBI database. When examining the affected sables, skin lesions were found, which were localized mainly in the back, waist, and sides. They were characterized by loss of guard hairs, alopecia, formation of crusts and scabs. Dark spots were often observed in the area of lesions from the side of the skin. Lesions were observed both in males and females, mainly in young animals. During visual examination, samples of pathological material were sticky bundles of hair (downy, less often guard hair) with dried crusts and scales at the base. The result of the fluorescent test with a Wood’s lamp in all samples was negative. Microscopy revealed bundles of downy hairs stuck together and a large amount of purulent debris, which made it difficult to detect fungal elements. As a result of cultural mycological analysis, 51 cultures were isolated, 18 taxa (species and genera) of fungi were identified. At the same time, keratinophilic dermatophyte fungi ( Arthroderma cuniculi , Chrysosporium carmichaelii , Chrysosporium spp.) were isolated from 12 % of the samples, probably acting as etiological agents of dermatosis. Growth of dermatophytes was observed only on the DTM-Expert selective differential diagnostic medium; fast-growing non-dermatophyte fungi grew on ordinary media. Non-dermatophyte fungi with keratinolytic properties were also isolated - Scopulariopsis brevicaulis (16 %), Acremonium spp. (14 %), Aspergillus spp. (36 %), which can act as secondary opportunistic pathogens.