Two methods of demonstrating leprosy bacilli in smears.

Two methods, the carbol fuchsin with acetic acid differentiation and the periodic acid-carbol pararosaniline, were used for demonstrating leprosy bacilli in skin smears. Bacillary smears from 200 long-treated patients with tuberculoid, borderline and lepromatous leprosy were stained with periodic acid-carbol pararosaniline. There were significantly greater BI and MI determinations than with classic carbol fucsin staining. With the former stain bacilli were found in 69 of 96 skin smears in which no bacilli could be seen by the latter stain. It is suggested that under the action of antileprosy drugs some leprosy bacilli may lose their acid-fastness and become chromophobic; chromophobic bacilli can be restored to their staining with periodic acid pretreatment. Leprosy bacilli in their chromophobic form can survive in healing and apparently healed lesions even after prolonged chemotherapy and can be a possible source of relapse.