Abstract: Objective To investigate the morphological characteristics during the invasion process in hair infection caused by Microsporum canis and its growth and proliferation in vitro.Methods Twenty children suffered from Microsporum canis-induced tinea alba or kerion were selected.The infected hairs and scales were taken for direct microscopic examination by 20% KOH preparation,fungal culture on Sabouraud's media and histopathological examination with PAS stain.Then the primary colonies were isolated,transinoculated to rice grain media and cultured at 25℃～28℃.The cultures were observed and photographed under a microscope 2 clays after the trans-inoculation.Results Micro-and macro-conidia as well as hyphae were found in the scales by the direct microscopic examination.In the infected hairs,there were mosaic spores with macroconidia outside the hair,or triple-layer structures with outer cell layer,macroconidia layer and microconidia layer sequentially from the exterior to the interior,and macroconidia inside the hair medulla.The histopathological examination showed different morphological features of fungi between the fungal sheath and the stump of broken hairs as well as hair roots.In the former,there was mosaic-like microconidia outside the hair while in the latter,large amount of hyphae and micro-as well as macro-conidia were inside the hair.The life cycle of Microsporum canis on the rice grain media presented a picture from conidia apparatus,early-stage macroconidia,mature macroconidia to new hyphae and pycnidia grown from macroconidia.New macroconidia continued to grow and new generation was produced,thus the fungi proliferated in cycles.Conclusions Microsporum canis is a zoophilic dermatophyte.The hyphae and spores invade into the hair tissue and cause the hair to break.The cycle of Microsporum canis on rice grain media is characterized by a new generation growth of hyphae and pycnidia from the macroconidia.

Key words: Microsporum, Infected hair, Proliferation