Dermatophilus congolensis and "hairy" leukoplakia.

The authors report the first human case (to our knowledge) of infection of the oral mucosa by Dermatophilus congolensis. Septate branching filaments morphologically identical to those of D. congolensis were identified in the lingual epithelium of a male homosexual employed as an animal handler. This actinomycete is the cause of dermatophilosis, a proliferative exudative dermatitis affecting many animal species. Clinical features suggested "hairy" leukoplakia (HL), a hyperkeratotic tongue lesion for which human papillomavirus (HPV) and Epstein-Barr virus (EBV) have been implicated as etiologic agents. Immunoperoxidase staining for HPV capsid antigen was negative. Direct immunofluorescent staining with a conjugate specific for D. congolensis identified the bacterial structures as those of this species while excluding morphologically similar organisms.