RESUMEN
Detection of parasites in clinical lesions is essential for a conclusive diagnosis of cutaneous or mucocutaneous leishmaniasis. Biopsies of experimentally infected animals were used to test a ribosomal DNA (rDNA) derived oligonucleotide (S3) as a diagnostic tool for leishmaniasis, Leishmania amazonensis were detected by that probe in dot blot assays containing RNA from experimentally induced BALB/c footpad lesions. RNA from a macrophage rich lesion induced by BCG infection yielded negative results. Specificity of S3 in differential diagnosis was also experimentally evidenced by the negative hybridization with nucleic acids of other infectious agents causing cutaneous lesions such Fonsecaea pedrosoi, Cladosporium carrionii, Phialophora verrucosa, Sporotrix schenkii, Histoplasma capsulatum and Paracoccidioides brasiliensis. In addition, comparison of S3 and 18S rDNA sequences of Mycobacterium tuberculosis, atypical mycobacteria, M. leprae and Treponema pallidum revealed a low degree of similarity. These data indicated that S3 can identify Leishmania species ande exclude the presence of other pathogens, which lead to misdiagnosis, in hybridization tests.