Clinically alone, i.e. on the basis of syphilis symptoms, the diagnosis cannot be made, since syphilis symptoms can vary greatly and are not specific. Therefore a microscopic and serological syphilis test must be performed. It is not possible to cultivate the bacterium T. pallidum on a culture medium. In the microscopic diagnosis of the syphilis test, a smear is taken from the skin and mucous membrane changes and the secretion obtained is examined under a dark field microscope. Under a normal light microscope the bacteria cannot be detected because they are too thin. In addition to the typical structure, small diameter, even coils, the rapid bending and stretching movement in the middle of the bacterial body is characteristic. A positive test result is evidence of the disease, but a negative result does not exclude syphilis. In serological diagnostics antibody screening tests are performed which are positive 2-4 weeks after infection. Antibodies are detected that have formed against antigens on the surface of the pathogenic bacteria. The TPHA test (T. pallidum hemagglutination test, today also called TPPA test) is a sensitive and highly specific search reaction in which antibodies against T. pallidum clump (agglutinate) red blood cells (erythrocytes) loaded with T. pallidum antigen. It becomes positive in the 2nd week after infection with syphilis and remains so for many years after the disease has healed (“seronar”). In the early primary stage it can still be negative. The test is used in cases of suspected syphilis, but also for routine screening in early pregnancy, of blood donors and blood preserves. Positive results require a confirmation test: In the FTA-ABS test (Fluorescence Treponema Antibody Absorption Test) the bacteria are fixed on a slide and brought together with blood serum, the liquid part of the blood. The antibodies in the blood serum then attach to the antigens of the bacteria. After rinsing the serum, the antibodies are again labeled with other antibodies carrying a fluorescent dye. Under the fluorescence microscope, the antibodies sought against the bacteria thus become visible. The FTA-ABS test, like the TPPH test, is positive in the 2nd week after infection and remains positive in the sense of a seron scar years after clinical healing. The VDRL test (Venereal Disease Laboratory Test), also known as cardiolipin flocculation test, is used for therapy and progress monitoring. This syphilis test is used for the detection of lipid-specific antibodies, which recede as the skin manifestations heal. Cardiolipin is an antigen extracted from the heart of cattle and bound to cholesterol particles. The loaded particles are brought together with the patient’s serum. In the positive case, flocculation (agglutination) occurs. This test becomes positive 4-6 weeks after infection or 1-3 weeks after the primary effect occurs. The amount of lipid-specific antibodies decreases rapidly as the external symptoms of syphilis heal and are no longer present after successful treatment. This quantity (titre) can be used to assess whether the therapy was successful or whether the syphilis was insufficiently treated. However, the VDRL test can also be positive for other diseases, so it is characteristic of, but not specific to, syphilis. A CSF test is done to confirm neurosyphilis in patients with neurological symptoms of syphilis and to detect or exclude asymptomatic neurosyphilis. Only antibodies in CSF that have also been produced in the CNS prove neurosyphilis, but not antibodies that have migrated from serum into CSF. This can be determined by comparing the titers of antibodies in CSF and serum. If the ratio of CSF titer to serum titer exceeds 2, neurosyphilis is suspected. Syphilis can manifest itself in many different ways, especially the symptoms of the skin can be very different: “Syphilis is the monkey among skin diseases”, i.e. it can fake almost any skin disease. Sometimes Roseola syphilitica is confused with drug exanthema, which is the result of drug intolerance. The painful ulcer molle, caused by the bacterium H. ducreyi, and other skin changes caused by infections (e.g. granuloma venerum) must be distinguished from the ulcer durum.
