What is syphilis? Syphilis is a sexually transmitted infection that is caused by the bacterium Treponema pallidum. The infection is diagnosed through blood tests for antibodies that are produced by the body in response to the bacteria. After a person is infected with syphilis, antibodies against T. pallidum remain in their blood for years. Based on certain values ​​from laboratory tests, it can be determined whether the infection was recent or occurred years ago. What are the symptoms of syphilis? Syphilis is also called “the great imitator” because it manifests itself with many different symptoms that often resemble the symptoms of other diseases. Common signs and symptoms of syphilis include: Painless, open sores (chancres) on the genitals, lips, or mouth; A rash on the body, usually on the palms of the hands or soles of the feet; Mild flu-like symptoms such as fever, fatigue, muscle aches and swollen lymph nodes Although symptoms such as these may indicate syphilis, only a blood test can definitively diagnose the infection. What are the blood tests for syphilis? Syphilis is usually diagnosed through a blood test. Less commonly, syphilis can be detected by examining a sample of body fluids under a microscope. The preferred method of testing for syphilis is a blood test. Two types of tests can detect and confirm syphilis using the same blood sample. Non-treponemal (non-specific) tests Diagnosis of syphilis begins with a non-treponemal blood test. This includes venereal disease research laboratory test (VDRL – Venereal disease research laboratory test) and rapid plasma reagin test (RPR – Rapid plasma reagin). Both tests detect antibodies (IgM and IgG to lipids in the cell wall of treponemas) that are produced by the body in response to damage caused by the infection. The VDRL test examines antibodies that are produced not only in syphilis, and for this reason this test does not always give an accurate result. The test can be performed on a blood sample or cerebrospinal fluid. The test is not useful in very early or very late stage infection. The result of the RPR test shows the state of the body at the time of the test. Antibodies against syphilis may not be detected weeks after exposure to the pathogen, necessitating repeated testing of patients at high risk of developing the infection. With proper treatment, the RPR test remains negative for up to 3 years. Therefore, its values ​​are an indicator of active (untreated) infection, reinfection (re-infection) or past infection (with a low antibody titer). Although non-treponemal tests are inexpensive and easy to administer, they have the potential for false-positive results (meaning they may show the presence of syphilis even when no such infection is present).Therefore, a positive result of these tests must be confirmed with a second, more expensive test. Treponemal (specific) tests If the result of the non-treponemal test is positive, one of several treponemal tests will be used to confirm the result, which include: Enzyme-linked immunosorbent assay (ELISA – Enzyme like immunoassay test) – which tests for antibodies to Treponema pallidum; Fluorescent Absorption of Treponemal Antibodies (FTA-ABS) – immunofluorescence test for antibodies in the infection; T. pallidum particle agglutination assay (TP-PA) Treponemal tests differ from non-treponemal tests in that they detect antibodies specific for T. pallidum rather than antibodies produced in response to damage caused by T. pallidum. The immunological window for syphilis corresponds to the period between the moment of contact with the infectious agent and the moment when the test can show the presence of the infection. The average window period for syphilis is 21 days. If a patient is tested during the immunological window period, a false-negative result may be obtained. For more certain results, it is necessary to wait until the end of the period. What are the methods of direct identification of syphilis? Dark-field microscopy Dark-field microscopy is a direct examination method that is used less often because it requires highly skilled laboratory workers. It is performed by taking a sample of body fluid – from a chancre (a small painless sore) or papules (small, firm growths) from the lining of the oral cavity and examining the fluids under a microscope. The test can also be performed on tissue samples or nasal secretions. With dark-field microscopy, it is possible to see the corkscrew-shaped bacteria under the microscope lens. The test can be useful during late-stage syphilis, when antibody levels are low and results from other tests are sometimes inconclusive. Dark-field microscopy is also useful for examining newborns with congenital syphilis, when syphilis is transmitted from mother to fetus during pregnancy. Congenital syphilis can be difficult to diagnose because the mother’s antibodies circulate in the baby’s blood during the first 12 to 18 months of its life. By examining the nasal secretions under a microscope, the lab can confirm whether the baby has T. Pallidum. Direct immunofluorescence test The direct immunofluorescence test (DFA) is performed by antibodies against syphilis (immunoglobulins) conjugated with fluorescein (an organic compound and dye), which are added to the sampled biological material. The results are read on a fluorescence microscope. Polymerase chain reaction Polymerase chain reaction (PCR) – a widely used laboratory method for amplification (creation of a very large number of copies) of selected short sections of specific DNA, used for the detection of bacterial nucleic acids of the treponema. References: 1. Ong JJ, Fu H,Smith MK, Tucker JD. Expanding syphilis testing: a scoping review of syphilis testing interventions among key populations 2. Centers for Disease Control and Prevention. Syphilis—CDC fact sheet (detailed) 3. Luo Y, Xie Y, Xiao Y. Laboratory diagnostic tools for syphilis: current status and future prospects 4. Henao-Martínez AF, Johnson SC. Diagnostic tests for syphilis: new tests and new algorithms 5. Klausner JD. The great imitator revealed: syphilis