Equine Dermatophytosis due to Trichophyton bullosum, a Poorly Known Zoophilic Dermatophyte Masquerading as T. verrucosum

Abstract

Trichophyton bullosum is a zoophilic dermatophyte from the Arthroderma benhamiae complex with a poorly known distribution. In this study, we report a case of dermatophytosis caused by T. bullosum in a 6-year-old male horse who had a skin lesion located in a saddle area. The infection spread rapidly to the upper chest and to both sides of the trunk. The dermatophyte was isolated in culture and identified by sequence analysis of the internal transcribed spacer regions (ITS rDNA). To date, this is the first verified case of animal infection due to T. bullosum in Europe following the 2012 report of human infection in France. We hypothesize that this species can be relatively common in horses and donkeys, but it is confused with other zoophilic species responsible for infections with similar clinical manifestations, and when isolated in culture, it is misidentified as the phenotypically similar T. verrucosum. Previous cases of dermatophytosis caused by T. verrucosum-like dermatophytes in horses and donkeys were reviewed together with human infections transmitted from these animals. This summary estimates possible distribution width of T. bullosum. The taxonomy of T. verrucosum-like dermatophytes is extremely difficult due to lack of original material and poor morphology of species. Molecular genetic methods are necessary to verify the identification of these fungi. ITS1 or ITS2 region of rDNA alone is sufficient for correct identification.

Epidemiologia de micoses, pitiose e micotoxicoses em equinos no sudeste do Rio Grande do Sul

“…No presente estudo, foi encontrado o complexo T. mentagrophytes como o principal agente causal das dermatofitoses equinas na região. Situação diversa da relatada na literatura, que cita Trichophyton equinum e Microsporum canis como os fungos que mais causam dermatofitose em equinos (Pereira et al 2006, Chermette et al 2008, Lyskova et al 2015. Uma importante implicação desse fato está na saúde pública, uma vez que o complexo T. mentagrophytes é uma espécie antropofílica muito mais comum e implicada em infecções humanas (Cafarchia et al 2013, Costa et al 1999, Silveira-Gomes et al 2013), enquanto T. equinum é zoofílico e raramente ocorre em humanos (Chabasse & Pihet 2008).…”

Resolving the taxonomy of emerging zoonotic pathogens in the Trichophyton benhamiae complex

“…Phenotypic criteria are usually relatively effective in routine diagnostics for major dermatophyte species or species complexes. However, as in other fungi, we have found similarities between species or morphotypes across unrelated dermatophytes, resulting in misdiagnosis in practice (Summerbell 2011, Lysková et al 2015. There is also considerable intraspecific phenotypic variability in other species or species complexes that is not correlated with molecular taxonomy (Heidemann et al 2010, Su et al 2019, Kandemir et al 2020.…”

“…27). It is distributed in Europe, North Africa and the Middle East (Lebasque 1933, Sitterle et al 2012, Lysková et al 2015, Sabou et al 2018.…”

“…Trichophyton verrucosum grows slowly in culture and frequently produces only chlamydospores as its main microscopic characteristic. In this respect, it is superficially very similar to T. bullosum, which causes infections in donkeys and horses, but is much less common and is geographically restricted to the Middle East, Africa and Europe (Sitterle et al 2012, Lysková et al 2015, Sabou et al 2018. Scant data are available on the distribution of T. eriotrephon, which is only known from several poorly documented cases of dermatophytosis in humans and dogs (Rezaei-Matehkolaei et al 2013, Hubka et al 2018c, Sabou et al 2018.…”

“…The Trichophyton benhamiae complex currently comprises six species: T. benhamiae, T. bullosum, T. concentricum, T. erinacei, T. eriotrephon and T. verrucosum (Lysková et al 2015, de Hoog et al 2017). These species are predominantly zoophilic, with the exception of anthropophilic T. concentricum, an agent of tinea imbricata in tropical regions (Bonifaz et al 2004, Pihet et al 2008, Bonifaz and Vazquez-Gonzalez 2011.…”