Syphilis

Tp, a spirochete bacterium, is the causative agent of the venereal disease syphilis. Although syphilis rates are declining in the United States after an epidemic outbreak between 1986 and 19901, the incidence of syphilis in Europe has increased since 1992, especially in the countries of the Russian Federation, where peaks of 263 cases per 100,000 have been reported 2. In 1995, WHO reported 12 million new cases of syphilis3. Currently, the positive rate of syphilis serological tests in HIV-infected individuals has been rising recently. Serological detection of anti-Tp antibody has been long recognized in the diagnosis of syphilis since the natural course of the infection was characterized by periods without clinical manifestations. Both IgM and IgG antibodies were detected in sera from patients with primary and secondary syphilis. The IgM antibody may be detectable towards the second week of infection, while IgG antibody appears later, at about 4 weeks4. These antibodies could last for several years or even decades in the serum of a patient with untreated latent syphilis 5. Antigens such as Rapid Plasma Cardiolipin antigen (RPR) and Tp bacterial extracts have been used in the syphilis serological tests for decades.However, RPR antigen is a non-treponema antigen, derived from bovine heart. Antibody to RPR antigen does not develop until 1-4 weeks after the appearance of the chancre, thus this antigen lacks of sensitivity to primary syphilis.