MOLECULAR-DETECTION OF TREPONEMA-PALLIDUM IN SECONDARY AND TERTIARY SYPHILIS

Treponema pallidum can be detected by conventional techniques such as dark-field microscopy, immunofluorescence or the rabbit infectivity te st, in large numbers in the skin lesions of primary and early secondar y syphilis. In the skin lesions of late secondary and tertiary syphili s, conventional techniques fail to detect spirochaetes in general, per haps due to increasing degeneration and the disappearance of treponema l spirochaetes in late syphilitic skin lesions. We used the highly sen sitive technique of polymerase chain reaction (PCR) to prove the prese nce of Treponema pallidum-specific DNA in six lesions of late secondar y syphilis and seven lesions of tertiary syphilis, including one syphi litic gumma, A Whartin-Starry stain was carried out in all 13 specimen s and did not reveal any treponemal structures. Treponema pallidum-spe cific DNA was amplified by PCR in four of six cases of secondary syphi lis and in the syphilitic gumma. These results are in favour of a dire ct cell-mediated immune reaction directed against treponemal antigen r ather than the concept of an Id-reaction. Beside the usefulness of a P CR-based assay for understanding the aetiology of lesions of late syph ilis, the assay described can be of clinical importance in various sit uations where traditional methods fail to detect Treponema pallidum be cause of lack of sensitivity.