[A case of black dot ringworm caused by Trichophyton tonsurans in Chiba Prefecture].

A 74-year-old woman visited a clinic in Kisarazu, Chiba Prefecture in December 2002 complaining of itching, scale and alopecia. She had been diagnosed as having tinea capitis by a direct microscopic examination of scales, and been treated with an antifungal cream and steroid lotion since 1999. The bald area spread from frontal to occipital in which multiple black dots and red papules were scattered. Abundant endothrix spores were observed in the hair shaft. A mycelial colony was isolated from the black dots. A giant colony on Sabouraud's agar was white, powdery and flattened with cottony elevation at the center in the obverse, and a reddish-brown pigmentation in the reverse. The isolate produced abundant microconidia that were round to club-and balloon-shaped with extreme swelling, while macroconidia and spiral bodies were few. Hair perforation test was negative and urease activity test was positive. ITS1-5.8S-ITS2 rDNA sequencing revealed 100% homology with T. tonsurans isolated from two old women in Niigata Prefecture. On the other hand, 3 bases were different from those of the outbreak isolates from judo and wrestling players infected through international matches. T. tonsurans has polymorphism and the present isolate might be an autochthonous genotype in Japan. This is the first time T. tonsurans was isolated in Chiba Prefecture. But this prefecture had been known as an endemic area of Trichophyton coccineum, which was very similar in morphological and physiological characteristics to those of T. tonsurans before World War II. These facts raise the question of whether T. tonsurans has existed in this prefecture before.