The clinical diagnosis of neurosyphilis, especially in HIV infected patients, can be extremely difficult. Serologic assays are the accepted methods for laboratory diagnoses. However, these assays lack sensitivity or specificity, especially in the diagnosis of neurosyphilis. In addition, individuals with HIV infection have been documented to lose their treponemal test reactivity to MHA-TP and FTA-ABS. Therefore, the need for the development of more effective methods to detect T. pallidum exists.
The specific aims of the """"""""pilot"""""""" project are to establish a sensitive and specific diagnostic test for the detection of T. pallidum infection based on the polymerase chain reaction (PCR) method, and to evaluate the performance of the PCR assay on well-characterized archived clinical specimens from patients with a clinical or histopathological diagnosis of neurosyphilis. Preliminary studies indicate that a highly sensitive and specific assay to detect T. pallidum based upon the PCR can be developed. A 210-bp sequence of the gene encoding the 47kDa membrane immunogen was amplified and the PCR products probed by DNA hybridization with a 40-bp fragment internal to the amplified DNA. The assay sensitivity is capable of detecting five or more organisms consistently and, in some cases, a single organism when calculated by sequential dilutions of suspensions of treponemes. The specificity of the 47kDa primer pairs/probe was assessed using a panel of pathogenic and non-pathogenic spirochetes. Positive amplification products were consistently detected only with DNA obtained from either T. pallidum or T. pertenue. Similar results were obtained when a second set of primers/probe from the T. pallidum 4D antigen were implemented. The PCR method will be optimized to accommodate the highly sensitive and specific detection of T. pallidum from clinical specimens. Well-characterized archived post-mortem clinical specimens with a clinical/histopathologic diagnosis of neurosyphilis will be processed to validate the PCR method. This approach will allow for a comparison of the sensitivity/specificity of PCR to the currently utilized serologic studies in the diagnosis of neurosyphilis. It is hoped that these pilot studies will provide a valuable diagnostic technique that can be utilized in the investigation of the pathogenesis of neurosyphilis.
