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Microsporum canis is a zoophilic dermatophyte and the most common fungus isolated from dogs and cats worldwide. To invade skin, this pathogen uses different enzymes, which may be associated with virulence, that contribute to the fungal pathogenicity. The aim of this study is to compare the expression of enzymes that may be associated with virulence, and thermotolerance of M. canis strains isolated from dogs, cats, and humans. The in vitro expression of the enzymes keratinase, catalase, urease, hemolysin, and aspartic protease was evaluated in 52 M. canis strains recently isolated from 14 human patients, 12 dogs, 15 symptomatic, and 11 asymptomatic cats. In addition, thermotolerance was assessed by comparative analysis of fungal growth at 25 °C and 35 °C. Keratinase activity was low in 34 and moderate in 18 strains. Aspartic-protease activity was low in 7, moderate in 33, and high in 12 strains. Hemolysin activity was low in 44 and moderate in 8 strains. All strains were classified as low producers of catalase. All but three strains produced urease in vitro, with a broad range of activity. The strains presented in vitro growth at the two studied temperatures were classified as presenting low (36.5%), medium (44.3%), or high (19.2%) thermotolerance. There was no statistically significant difference in the new putative virulence-associated factors studied among the different hosts, which suggests that they may have a similar role on human, cat, and dog infection. Also, no difference was observed between strains isolated from symptomatic and asymptomatic cats. This suggests that these factors have a limited impact on the fate of feline dermatophytosis caused by M. canis.

Background: Tinea capitis, a common clinical pattern of dermatophyte infection in children is becoming a public health hazard in some countries. Several studies have reported terbinafine to be a safe and well-tolerated fungicidal drug for the treatment of this infection. However, the optimal treatment duration for its use in the treatment of tinea capitis caused by Microsporum species has not yet been determined., Objective: (i) To establish the optimal duration for terbinafine treatment to bring about complete cure of tinea capitis due to Microsporum infection in a large paediatric population, and (ii) to obtain information on the maximum therapeutic effect of the existing therapy., Patients and Methods: This parallel-group, double-blind, multicentre study was conducted in Europe and South America. Patients were randomized to one of four oral terbinafine treatment arms (6, 8, 10 or 12 weeks treatment) or to an open label, 12-week, high-dose griseofulvin (20 mg x kg(-1) x day(-1)) arm at a 1 : 1 : 1 : 1 : 1 ratio. All patients were followed up for 4 weeks after the end of the treatment phase., Results: In this group of 134 intention-to-treat patients, effective treatment was observed at the end of study in 62% of patients treated with terbinafine for 6 weeks and in 63% treated for 8 weeks. Mycological cure was obtained in 59% and 57%, respectively, and clinical cure in 76% and 80%. In the griseofulvin group, effective treatment was 88%, mycological cure was 76% and clinical cure 96%. However, these high rates were believed to be due to the high dosage of this drug and the prolonged course of treatment. Complete cure was observed at the end of study in 62% patients treated with terbinafine for 6 weeks, in 60% treated for 8 weeks and in 84% patients treated with griseofulvin for 12 weeks., Conclusions: Although there was no statistical trend between the duration of terbinafine treatment within the groups for complete cure at the end of study, there was a positive correlation between the daily dose of terbinafine (mg x kg(-1)) and complete cure. Terbinafine therapy for 6 weeks could represent an alternative to griseofulvin for the treatment of Microsporum tinea capitis. However, further clinical trials are required in order to optimize the dose regimen to allow higher cure rates to be reached.