Cat favus caused by Microsporum incurvatum comb. nov.: the clinical and histopathological features and molecular phylogeny

Favus is a distinctive form of infection that is caused by exclusively dermatophytes. Its clinical presentation is characterized by scutula, which are concave, thick fungal crusts. The best-known examples of human scalp favus are caused by Trichophyton schoenleinii and those of mouse favus are caused by T. quinckeanum. However, other dermatophytes, such as T. violaceum, T. verrucosum, Microsporum audouinii, M. gallinae, M. gypseum, and M. canis, have been reported sporadically to cause favic lesions. Favus on cats has rarely been mentioned in the literature, and the pathogens with which it has been associated are, for the most part, unknown. Here, we examine four cat favus cases, focusing on clinical presentations and histopathological features. In all cases the etiologic agent was identified as M. incurvatum based on its morphological characteristics and sequences of internal transcribed spacers (ITS) of nuclear ribosomal DNA. Phylogenetic analysis using the neighbor-joining method, which is based on ITS, showed that these four isolates belonged to two strains of M. incurvatum; one strain was a new combination from the basionym Nannizzia incurvata.