2 Clinical Issues in Basic Medical Research
in Dermatophytosis
2.1 Epidemiological Background of Dermatophytosis
Dermatophytosis, which is a common infectious disease of the keratinized tissues in
the skin, hair, and nails, is caused by dermatophytes (Osborne, Leitner, Favre, &
Ryder, 2005) and affects a large proportion of the population (Vander Straten,
Hossain, & Ghannoum, 2003). There are three known genera of dermatophytes:
Epidermophyton, Microsporum, and Trichophyton. Among these, Trichophyton
mentagrophytes, Trichophyton tonsurans, and Trichophyton rubrum are the most
common pathogens, with T. rubrum being the most prevalent isolated organism
(Osborne et al., 2005). T. rubrum, among other dermatophytes, is a major causative
agent for superficial dermatomycosis like onychomycosis and tinea pedis (Kemna &
Elewski, 1996). These studies suggest that the scattering rate is very high, more than
65.0%, from patients suffering from tinea pedis. Our epidemiological survey
targeted 160 people in 2016 and found that the scattering rate of Trichophyton
species on feet is very high 29.3%, and 55.6% in the elderly population older than
60 years (Suzuki, Fujitani, et al., 2018a, 2018b). Nevertheless, especially in special
nursing care homes for the elderly, no appropriate treatment is available, and cases
were found in which the wrong antifungal drugs were administered. The potential for
the development of drug-resistant fungi that is promoted by misuse of antifungal
drugs is a concern.
Overall, clinically, about 20% of the population is reported to have tinea pedis,
and about 10% have tinea unguium in Japan. More than 13% of new dermatology
patients have ringworm; the frequency of each type is as follows: foot ringworm is
approximately 64%, nail ringworm 20%, body ringworm 7%, and hip ringworm 5%
(Onozaki, Makimur, et al., 2009). If limited to foot skin diseases, 40% of cases are
tinea pedis. Regarding direct infection from animals to humans, Trichophyton
verrucosum is found in cattle handlers including dairy farmers, and Microsporum
canis from cats as companion animals, and T. mentagrophytes from rabbits or
rodents are present. Body ringworm by animal type and head ringworm are the
main problems. A characteristic of ringworm due to estrogenic fungi is that symptoms are often mild or asymptomatic in the host animal (Yamada, Makimura, et al.,
2006).
2.2 Emergence of Resistant Fungi
In recent years, filamentous fungi with low sensitivity to antifungal agents have been
reported in various countries. NFI5146 shows cross-resistance to naftifine, an
allylamine antifungal agent, and butenafine, a benzylamine antifungal agent
(Mukherjee et al., 2003). Allylamine and butenafine antifungal agents inhibit
Realities and Challenges of Bridging Research in Japan
141
in Dermatophytosis
2.1 Epidemiological Background of Dermatophytosis
Dermatophytosis, which is a common infectious disease of the keratinized tissues in
the skin, hair, and nails, is caused by dermatophytes (Osborne, Leitner, Favre, &
Ryder, 2005) and affects a large proportion of the population (Vander Straten,
Hossain, & Ghannoum, 2003). There are three known genera of dermatophytes:
Epidermophyton, Microsporum, and Trichophyton. Among these, Trichophyton
mentagrophytes, Trichophyton tonsurans, and Trichophyton rubrum are the most
common pathogens, with T. rubrum being the most prevalent isolated organism
(Osborne et al., 2005). T. rubrum, among other dermatophytes, is a major causative
agent for superficial dermatomycosis like onychomycosis and tinea pedis (Kemna &
Elewski, 1996). These studies suggest that the scattering rate is very high, more than
65.0%, from patients suffering from tinea pedis. Our epidemiological survey
targeted 160 people in 2016 and found that the scattering rate of Trichophyton
species on feet is very high 29.3%, and 55.6% in the elderly population older than
60 years (Suzuki, Fujitani, et al., 2018a, 2018b). Nevertheless, especially in special
nursing care homes for the elderly, no appropriate treatment is available, and cases
were found in which the wrong antifungal drugs were administered. The potential for
the development of drug-resistant fungi that is promoted by misuse of antifungal
drugs is a concern.
Overall, clinically, about 20% of the population is reported to have tinea pedis,
and about 10% have tinea unguium in Japan. More than 13% of new dermatology
patients have ringworm; the frequency of each type is as follows: foot ringworm is
approximately 64%, nail ringworm 20%, body ringworm 7%, and hip ringworm 5%
(Onozaki, Makimur, et al., 2009). If limited to foot skin diseases, 40% of cases are
tinea pedis. Regarding direct infection from animals to humans, Trichophyton
verrucosum is found in cattle handlers including dairy farmers, and Microsporum
canis from cats as companion animals, and T. mentagrophytes from rabbits or
rodents are present. Body ringworm by animal type and head ringworm are the
main problems. A characteristic of ringworm due to estrogenic fungi is that symptoms are often mild or asymptomatic in the host animal (Yamada, Makimura, et al.,
2006).
2.2 Emergence of Resistant Fungi
In recent years, filamentous fungi with low sensitivity to antifungal agents have been
reported in various countries. NFI5146 shows cross-resistance to naftifine, an
allylamine antifungal agent, and butenafine, a benzylamine antifungal agent
(Mukherjee et al., 2003). Allylamine and butenafine antifungal agents inhibit
Realities and Challenges of Bridging Research in Japan
141