Trichophyton mentagrophytes, T. quinckeanum, and T. interdigitale
In the past, T. mentagrophytes complex was divided into numerous anthropophilic or zoophilic varieties associated with multiple sexual states (A. Vanbreuseghemii, A. benhamiae, and A.
simii) (Takashio 1977; Hironaga and Watanabe 1980; Hejtmanek and Hejtmankova 1989). Phylogenetic analyses resolved the status of these varieties, some of them were elevated to a species level, others became superfluous (Graser et al. 1999b; de Hoog et al. 2017). The data also confirmed that three sexual states attributed in the past to T. mentagrophytes represent separate species complexes. The concept of T. interdigitale (former T. mentagrophytes var. interdigitale) and T. mentagrophytes s. str. has changed significantly during the last two decades especially in connection with their neotypification by Graser et al. (1999b). The selection of neotype (closely phylogenetically related to T. schoenleinii) changed significantly the practical use of the well-known name T. mentagrophytes that became rare species in clinical practice. The concept of “anthropophilic and zoophilic strains of T. interdigitale” was used instead for a transitional period (Nenoff et al. 2007; Heidemann et al. 2010), and consequently, the majority of isolates previously identified as T. mentagrophytes were relabeled as zoophilic strains of T. interdigitale. The selection of neotype of T. mentagrophytes was subsequently disputed by several authors (Sun et al. 2010; Beguin et al. 2012; Chollet et al. 2015a), and in the light of new arguments, an alternative neotype was designated by de Hoog et al. (2017). Although the validity of this neotype may be subject of future nomenclature debate, we follow here the recently designated neotype that returns the name T. mentagrophytes back to common use together with the name T. quinckeanum, an agent of mouse favus. In contrast to Heidemann et al. (2010), no clear relationship between origin, morphology of the strains, genotype, and clinical manifestation was found in isolates of T. interdigitale/T. mentagrophytes from Tunisia (Dhib et al. 2017). These conclusions are in agreement with our observation in strains from Czech patients and may suggest that T. interdigitale and T. mentagrophytes sensu de Hoog et al. (2017) are conspecific.The reservoir of T. mentagrophytes are rodents, hunting cats (rather than indoor cats), dogs, and less commonly other animals such as ruminants and horses. When transmitted to human, infection usually manifest as inflammatory tinea of glabrous skin (tinea corporis, faciei, barbae), less frequently as tinea capitis (Frealle et al. 2007; Cafarchia et al. 2013c). The isolates are usually typical by colonies in shades of beige and granular/powdery colony texture; numerous microconidia, macroconidia, and spiral hyphae can be usually observed in microscope slides. Mating of isolates with opposite mating types leads to production of a sexual state corresponding to former A. Vanbreuseghemii. In contrast, anthropophilic T. interdigitale represent a clonal lineage (only single mating type) derived from sexual zoophilic lineage that lost the ability to mate with them. The colonies of anthropophilic strains are usually white and cottony; micromorphology is typical by the presence of microconidia and the absence of macroconidia and spiral hyphae. These strains are almost exclusively associated with onychomycosis and tinea pedis in human and absent in animals (Nenoff et al. 2007; Heidemann et al. 2010).
Trichophyton mentagrophytes is distributed worldwide. It is currently a major cause of dermatophytosis in rabbits (Fig. 3.6) and other rodents (except guinea pigs) followed by much less frequent M. canis, T. benhamiae, and others (Hoppmann and Barron 2007; Cafarchia et al. 2010, 2012; Kraemer et al. 2012). The transmission from pet rabbits to humans (mostly children) is well known, and the individual cases manifest usually as tinea capitis or corporis (Van Rooij et al. 2016; Zhang et al. 2009). Rabbitries constitute an important reservoir of the disease, and their environment can be heavily contaminated.
Widespread dermatophytosis in young rabbits impacts profoundly on animal health along with bacterial superinfections (caused mostly by staphylococci). The infected animals have lower indices in prolificacy and growth, and the severely infected individuals usually have to be discarded, thus reducing productivity and causing financial loss (Moretti et al. 2013). Recurring disease is reported in rabbit farm workers (Torres-Rodriguez et al. 1992; Van Rooij et al. 2016). Significant outbreaks due to T. mentagrophytes in animals have been infrequently reported (Alteras and Cojocaru 1969; Mesquita et al. 2016) or are underreported. The prevalence in animals is frequently very high and may be neglected due to high percentage of asymptomatic animals. For instance, a study was conducted on 220 Spanish rabbit farms, and 79.5% of the examined animals were positive for T. mentagrophytes that corresponds to 98% of all isolated dermatophytes (Torres-Rodriguez et al. 1992). In another study from Spain, dermatophytes were cultured from 83% of rabbits with suspected dermatophytosis, and T. mentagrophytes (69.2%) was the most abundant pathogen (Cabanes et al. 1997). Similar situation has been found in Italy, where dermatophytosis was found in ~60-87% rabbit farms and T. mentagrophytes represented ~92-93% of isolated dermatophytes. Higher temperature and relative humidity or inadequate and infrequent disinfection practices were identified as the most significant risk factors for dermatophytosis in rabbit farms (Cafarchia et al. 2010). Young animals or animals in fattening and finishing stages are the most frequently infected (Cafarchia et al. 2010; Moretti et al. 2013). It has been shown that the ITS sequences of T. mentagrophytes isolates from rabbits from southern Europe countries were identical, but different from those isolated from dogs and cats or rabbits from Asia. These results may suggest that a particular genotype could be prevalent in rabbits in southern Europe (Mesquita et al. 2016). Several outbreaks involving up to dozens of human patients have also been described and transmitted from rabbits (Alteras and Cojocaru 1969;Veraldi et al. 2012; Mesquita et al. 2016) and horse (Chollet et al. 2015b). Chinchillas are also vulnerable to infection, and T. mentagrophytes is isolated from ~5 to 10% of asymptomatic fur-ranched or pet chinchillas and 30% of animals with fur damage (Donnelly et al. 2000; Moretti et al. 2013). The infections in dogs and cats occur regularly through the world, but the infection counts are usually relatively low compared to M. canis (Lewis et al. 1991; Mancianti et al. 2002; Khosravi and Mahmoudi 2003; Cafarchia et al. 2004; Seker and Dogan 2011). Significantly higher infection rates are detected in free roaming, feral, and hunting dogs and cats in which T. mentagrophytes can even prevail over M. canis (Drouot et al. 2009; Duarte et al. 2010).
Trichophyton quinckeanum is a species historically associated with favus in rodents and rarely isolated from human infections (mostly tinea of glabrous skin). It is reasonable that this fungus is even rarer today because of improved living conditions. Its closest relatives are anthropophilic T. schoenleinii (an agent of tinea capitis typical by scutula formation) and probably geophilic T. simii. The morphology of T. quinckeanum is nearly indistinguishable from T. mentagrophytes, although the species are phylogenetically distinct (Fig. 3.3). Trichophyton quinckeanum has not been detected at all in majority of published epidemiological studies on human and animal dermatophytoses supported by molecular data. The exception is a recent report of 62 infections in human patients in Germany (tinea of glabrous skin and tinea capitis) (Uhrlaβ et al. 2018). Interestingly, all cases were diagnosed during a 3-year period (2013-2017) in a single laboratory, and no cases were detected during previous years despite molecular verification of identification. Cats were identified as a source of infection in several patients, and all isolates had a unique ITS genotype that was different from all previously examined European and Asian strains. This suggests a clonal spread of a new genotype.
3.7.3