A SEVENTEEN-YEAR SURVEY OF THE RINGWORM FLORA OF BIRMINGHAM

Current Topics in Dermatophyte Classification and Clinical Diagnosis

Dermatophytes are highly infectious fungi that cause superficial infections in keratinized tissues in humans and animals. This group of fungi is defined by their ability to digest keratin and encompasses a wide range of species. Classification of many of these species has recently changed due to genetic analysis, potentially affecting clinical diagnosis and disease management. In this review, we discuss dermatophyte classification including name changes for medically important species, current and potential diagnostic techniques for detecting dermatophytes, and an in-depth review of Microsporum canis, a prevalent zoonotic dermatophyte. Fungal culture is still considered the “gold standard” for diagnosing dermatophytosis; however, modern molecular assays have overcome the main disadvantages of culture, allowing for tandem use with cultures. Further investigation into novel molecular assays for dermatophytosis is critical, especially for high-density populations where rapid diagnosis is essential for outbreak prevention. A frequently encountered dermatophyte in clinical settings is M. canis, which causes dermatophytosis in humans and cats. M. canis is adapting to its primary host (cats) as one of its mating types (MAT1-2) appears to be going extinct, leading to a loss of sexual reproduction. Investigating M. canis strains around the world can help elucidate the evolutionary trajectory of this fungi.

Analysis of the dermatophyte species isolated in the British Isles between 1980 and 2005 and review of worldwide dermatophyte trends over the last three decades

Infections of the skin, hair and nails by dermatophyte fungi are common in developed and developing countries alike. However, the species involved and the resulting clinical entities vary both geographically and with time. We have surveyed 15,333 dermatophytes obtained from primary isolations at the Mycology Reference Laboratory, Bristol, UK from 1980 through 2005. Several striking trends in dermatophyte prevalence were apparent over this period. The relative frequencies of isolations of Microsporum canis (cat and dog ringworm), Trichophyton verrucosum (cattle ringworm), T. mentagrophytes var. mentagrophytes (rodent ringworm) and Epidermophyton floccosum (a cause of human groin and foot infections) all decreased by 90%. Conversely, the contributions of T. tonsurans and T. violaceum (two anthropophilic scalp-infecting species) to total dermatophyte isolations increased by 1000% over the same period. Finally, T. rubrum and T. mentagrophytes var. interdigitale, the two common causes of foot infection comprised 80% of all dermatophytes isolated in 1980 and 90% of isolations in 2005. Similar trends in dermatophyte prevalence were evidenced throughout the British Isles, based on the voluntary reporting of isolations from a large number of British laboratories at 5-yearly intervals over the same period. The implications of these changing patterns of dermatophyte species, and the clinical entities they produce are discussed in the context of a review of worldwide dermatophyte isolations over the last three decades, with emphasis on the causal agents of tinea capitis.

A randomized comparison of 4 weeks of terbinafine vs. 8 weeks of griseofulvin for the treatment of tinea capitis

BACKGROUND

Tinea capitis is a common childhood infection that has recently become more frequent in urban areas in Europe and the U.S.A. The current licensed treatment in children is griseofulvin 10 mg kg(-1) daily, which is usually given for 6--8 weeks.

OBJECTIVES

To compare this treatment with a 4-week course of oral terbinafine.

METHODS

Terbinafine was given at the following doses: in children weighing < 20 kg, 62.5 mg daily; 20--40 kg, 125 mg daily; > 40 kg, 250 mg daily. Two hundred and ten children aged 2--16 years, with mycologically confirmed tinea capitis, were randomized to 4 weeks treatment with terbinafine or 8 weeks with griseofulvin, and followed for a total of 24 weeks to determine the difference between treatments with respect to short- and long-term efficacy and tolerability.

RESULTS

One hundred and forty-seven patients were evaluable (terbinafine 77, griseofulvin 70). Although the 4-week course of terbinafine resulted in a trend to more rapid clearance of tinea capitis, there were no statistically significant differences between the two drugs in terms of overall outcome or tolerability, apart from in a subgroup of patients with Trichophyton infections, and weighing > 20 kg, who responded better to terbinafine than to griseofulvin at 4 weeks. By contrast, there was a better response to griseofulvin than to terbinafine in patients with Microsporum audouinii infections.

CONCLUSIONS

Overall, the study showed that 4 weeks of treatment with oral terbinafine has similar efficacy to 8 weeks of treatment with griseofulvin for the management of tinea capitis in children.

Tinea capitis

Tinea capitis is a common dermatophyte infection of the scalp in children. Dermatophytes are classified into three genera; tinea capitis is caused predominantly by Trichophyton or Microsporum species. On the basis of host preference and natural habitat, dermatophytes are also classified as anthropophilic, geophilic and zoophilic. The etiological agents of tinea capitis usually fall in the first and last categories. In North America, tinea capitis is now predominantly due to Trichophyton tonsurans. During the past 100 years the most common North American organism for tinea capitis was initially Microsporum canis followed later by M. audouinii. In other parts of the world the epidemiology varies. Tinea capitis is generally observed in children over the age of 6 years and before puberty, with African Americans being the most affected group. Clinical presentations are seborrheic-like scale, 'black dot' pattern, inflammatory tinea capitis with kerion and tiny pustules in the scalp. The clinical diagnosis should be confirmed by mycological examination. Wood's light examination was of value in diagnosing tinea capitis due to M. canis and M. audouinii; however, it is not helpful in T. tonsurans tinea capitis. Asymptomatic carriers may be a significant reservoir of infection and spread of spores may also involve inanimate objects. Carriers may benefit from shampooing their hair. Treatment of tinea capitis requires an oral antifungal agent. The data from the use of terbinafine, itraconazole and fluconazole are promising and suggest that these agents have an efficacy similar to griseofulvin while shortening the duration of therapy. Both griseofulvin and the newer antimycotics have a favorable adverse-effect profile and are associated with high compliance.

Tinea capitis: an overview with emphasis on management

Tinea capitis is perhaps the most common mycotic infection in children. In North America the epidemiology of tinea capitis has changed so that Trichophyton tonsurans now predominates over Micro-sporum audouinii. With this transition the utility of the Wood's light for diagnosis has been reduced since T. tonsurans infection is Wood's light negative. Griseofulvin has been the mainstay of therapy for the last 40 years. The newer antifungal agents-itraconazole, terbinafine, and fluconazole-appear to be effective and safe for the treatment of tinea capitis. When tinea capitis is due to T. tonsurans or other endothrix species the following regimens have been used: itraconazole continuous regimen (5 mg/kg/day for 4 weeks), itraconazole pulse regimen with capsules (5 mg/kg/day for 1 week plus 1-3 pulses 3 weeks apart), and itraconazole pulse regimen with oral solution (3 mg/kg/day for 1 week plus 1-3 pulses 3 weeks apart). With terbinafine tablets the continuous regimen (>40 kg body weight, 250 mg/day; 20-40 kg, 125 mg/day; and <20 kg, 125 mg/day) is given for 2 to 4 weeks. Fluconazole tablets or oral suspension (6 mg/kg/day) were administered for 20 days in one trial. Another possibility may be 6 mg/kg/day for 2 weeks and evaluating the scalp 4 weeks later. An extra week of therapy (6 mg/kg/day) can be administered if clinically indicated at that time. A once-weekly regimen may also be effective. When ectothrix organisms (e.g., Microsporum canis) are present, a longer duration of therapy may be required. The data suggest that the newer agents are effective, safe with few adverse effects, and have a high benefit:risk ratio. It remains to be seen to what extent griseofulvin will be superseded for the treatment of tinea capitis. Adjunctive therapies may help decrease the risk of infection to other individuals. Appropriate measures should be taken to reduce the possibility of reinfection.

The emergence of Trichophyton tonsurans tinea capitis in Birmingham, U.K

The anthropophilic fungus Trichophyton tonsurans is a cause of tinea capitis in children. Since the 1950s the organism has spread from Central to North America. A similar recent emergence of T. tonsurans has not been reported previously in the U.K. T. tonsurans was found to have become the predominant cause of tinea capitis in Birmingham, U.K., accounting for 72% of infections investigated in 1993. The symptoms and signs of the infection were variable and accurate diagnosis may be initially difficult. It is, thus, important to be aware of the emergence of T. tonsurans in the U.K., so that an early diagnosis can be made to facilitate appropriate treatment and to prevent spread of infection to close contacts.

Geographical distribution of the dermatophytes: a review

In these days of rapid transit from continent to continent, and the increasing mobility of people, agents of disease are no longer geographically restricted. Disease contracted half way across the world may become manifest in a country in which the pathogen is not normally found. Thus knowledge of the geographical distribution of pathogens becomes increasingly important when a diagnosis is being made. This is as true of ringworm fungi as of any other group of microorganisms. In the last 12 years, in the Mycological Reference Laboratory, an increasing number of exotic dermatophytes have been seen, related in part at least to the great increase in the number of non-British residents. Not all species of dermatophytes are cosmopolitan in their distribution throughout the world. While some have been recorded from every continent, others have geographically limited areas of greater or lesser extent. Surveys taken at intervals in a country may show a rise and fall in occurrence of several species as habits change, populations move and medical facilities became increasingly well-distributed. There have been few geographical surveys of ringworm fungi that have covered the world. Ajello (1960, 1974) has reviewed the individual species with regard to geographical location, while Vanbreuseghem & de Vroey (1970) attempted to estimate the relative importance of the various species in terms of numbers of isolations reported. This paper therefore reviews the world dermatophyte flora in terms of the dominant agents in the various countries, and some of the changes that have been recorded.