Trichophyton tonsurans as a cause of onychomycosis

Onychomycosis of the Middle Finger of a Japanese Judo Athlete due to Trichophyton tonsurans

We present a 17-year-old Japanese male high school student, who had applied steroid ointment for atopic dermatitis, with fingernail onychomycosis due to Trichophyton tonsurans. He was found positive for T. tonsurans infection based on hairbrush culture performed due to an epidemic of T. tonsurans infection in his judo club. The hairbrush culture method is very important in screening for this infection, and dermatologists should examine the entire body of athletes who are found positive using this method. For the diagnosis of T. tonsurans infection, other than the skin and hair, the nails should also be checked by dermoscopy because the fingernail may be the origin of this fungus.

[Infections of finger and toe nails due to fungi and bacteria]

Infections of the finger and the toe nails are most frequently caused by fungi, primarily dermatophytes. Causative agents of tinea unguium are mostly anthropophilic dermatophytes. Both in Germany, and worldwide, Trichophyton rubrum represents the main important causative agent of onychomycoses. Yeasts are isolated from fungal nail infections, both paronychia and onychomycosis far more often than generally expected. This can represent either saprophytic colonization as well as acute or chronic infection of the nail organ. The main yeasts causing nail infections are Candida parapsilosis, and Candida guilliermondii; Candida albicans is only in third place. Onychomycosis due to molds, or so called non-dermatophyte molds (NDM), are being increasingly detected. Molds as cause of an onychomycosis are considered as emerging pathogens. Fusarium species are the most common cause of NDM onychomycosis; however, rare molds like Onychocola canadensis may be found. Bacterial infections of the nails are caused by gram negative bacteria, usually Pseudomonas aeruginosa (recognizable because of green or black coloration of the nails) but also Klebsiella spp. and gram positive bacteria like Staphylococcus aureus. Treatment of onychomycosis includes application of topical antifungal agents (amorolfine, ciclopirox). If more than 50 % of the nail plate is affected or if more than three out of ten nails are affected by the fungal infection, oral treatment using terbinafine (in case of dermatophyte infection), fluconazole (for yeast infections), or alternatively itraconazole are recommended. Bacterial infections are treated topically with antiseptic agents (octenidine), and in some cases with topical antibiotics (nadifloxacin, gentamicin). Pseudomonas infections of the nail organ are treated by ciprofloxacin; other bacteria are treated according to the results of culture and sensitivity testing.

[Fungal nail infections - an update. Part 2 - From the causative agent to diagnosis - conventional and molecular procedures]

Trichophyton (T.) rubrum is the most frequently isolated dermatophyte in onychomycosis, both in Germany and worldwide. T. interdigitale (formerly T. mentagrophytes var. interdigitale) follows in second place. A further however rarely isolated dermatophyte in onychomycosis is Epidermophyton floccosum. Candida parapsilosis, Candida guilliermondii, and Candida albicans, followed by Trichosporon spp. are the most important yeasts which are found in onychomycosis. The molds most often responsible include Scopulariopsis brevicaulis, and several Aspergillus species, e. g. Aspergillus versicolor, and Fusarium spp. These so called non-dermatophyte molds (NDM) are increasingly isolated as emerging pathogens in onychomycosis. The diagnosis of onychomycosis should be verified in the mycology laboratory. Conventional diagnostic methods include the direct examination, ideally using fluorescence staining with Calcofluor® or Blancophor®, and culture. However, new molecular biological methods primarily employing the polymerase chain reaction (PCR) for direct detection of dermatophyte DNA in skin scrapings and nail samples have been introduced into routine mycological diagnostics. The diagnostic sensitivity is higher when both conventional and molecular procedures are combined.