Introduction
Testing for syphilis should be done on patients who exhibit infection-related signs or symptoms as well as asymptomatic individuals who are highly susceptible to infection or transmission to others. Syphilis is diagnosed using a combination of non-treponemal and treponemal serologic tests; a single test result should not be used to make the diagnosis. Furthermore, when diagnosing and staging a patient, the patient's clinical history and symptoms must be taken into account.
Treponemal tests (FTA, TP-PA, EIA), often known as confirmatory tests, identify syphilis-specific antibodies. Following an acute infection, treponemal antibodies will manifest sooner than non-treponemal antibodies. The antibodies found in these tests typically do not go away even after a successful course of treatment. As a result, a reactive treponemal test can reveal a history of or present infection with syphilis.
Any time during the course of syphilis, T. pallidum can infect the central nervous system (CNS), leading to neurosyphilis. Within the first few months or years of infection, early neurologic clinical signs of syphilitic meningitis (such as cranial nerve dysfunction, meningitis, meningovascular syphilis, stroke, and abrupt altered mental status) are typically observed. Ten to more than thirty years after infection, late neurologic symptoms such as widespread paresis (mild to moderate muscle weakening) and tabes dorsalis (a slowly progressing parenchymatous degenerative condition of the spinal cord's dorsal column and dorsal root) appear.
What Are the Treponemal Tests for Syphilis?
Clinical laboratories occasionally use automated treponemal immunoassays, usually by EIA or CIA, (enzyme immunoassay or chemiluminescence immunoassay) to screen syphilis serologic samples. This syphilis testing reverse sequence algorithm can detect people who have had syphilis treatment in the past, people who have untreated or insufficiently treated syphilis, and people who may have false-positive findings with little risk of infection. In order to inform patient management options, individuals who have a positive treponemal screening test should have a standard quantitative nontreponemal test with titer conducted immediately by the laboratory. In the event that the nontreponemal test yields negative results, the laboratory ought to conduct an alternative treponemal test, such as TP-PA or a treponemal assay that utilizes distinct antigens from the initial test, in order to evaluate the initial test's findings.
People with a history of prior treatment do not need any additional management if a second treponemal test (e.g., EIA reactive, RPR nonreactive, TP-PA reactive) is positive unless their sexual history suggests a reexposure. In this case, it is advised to assess for early infection by performing a second nontreponemal test two to four weeks following a verified medical history and physical examination.
A treponemal antibody test may be used first by the doctor for screening purposes, and a nontreponemal antibody test may be used to confirm a positive result. Reverse sequence testing is the name given to this testing technique.
Less popular techniques for syphilis detection involve searching for the bacteria or testing for its genetic material. Among these tests are:
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Darkfield Microscopy: This technique uses a sample of fluid from a lymph node or a skin sore to identify syphilis. The Treponema pallidum bacteria appear brilliant against a black backdrop when examined under a specially constructed microscope, which is used to analyze the sample.
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Polymerase Chain Reaction (PCR): This method finds the DNA, or genetic material, of the Treponema pallidum bacteria.
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Treponema Pallidum Immobilisation Test: The virulent T. pallidum (Nichol's strain) that was isolated from rabbits is used in this test. It finds an antibody (specific treponemal immobilizing antibody) that prevents T. pallidum from moving normally when a complement is present. Using dark field microscopy, the response of treponemes to patient serum is monitored.
The test is considered positive if 50 percent or more of the treponemes are immobilized. A few days to a week after the VDRL test, it turns positive. Specificity is 100 percent, but because the test is costly, time-consuming, and dangerous, it is not carried out in the modern world.
The following treponemal assays are now in use:
Treponema Pallidum Hemagglutination Assay:
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T. pallidum (Nichol's strain) is coated on sensitized sheep erythrocytes in the micro hemagglutination assay for IgM and IgG antibodies.
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Reactive results are those where agglutination happens at a dilution of 1:80 or higher.
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Reactivity should be anticipated after the fourth or fifth week of infection.
Fluorescent Treponemal Antibody Absorption Test:
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Antibody test for indirect immunofluorescence.
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Fluorescence indicates the presence of an antibody in the patient's serum. Fluorescence intensity is classified as reactive, borderline, or nonreactive.
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After the third week of infection, reactivity starts.
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In the early stages of syphilis, it is the most sensitive serological test available.
Fluorescent Treponemal Antibody Absorption Double-Staining Test:
In order to identify antibodies in the patient's serum, this test uses a fluorochrome-labeled counterstain for T. pallidum and an antihuman IgG conjugate labeled with tetramethylrhodamine isothiocyanate. In one percent of sera, false positives can occur.
Tissue-Specific Enzyme Immunoassay
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This test involves fixing antigens to microtiter plate wells, adding serum, and then rinsing everything off after 30 to 60 minutes.
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In the second incubation, an enzyme-labeled antihuman globulin reacts with the antigen that the T. pallidum antibody has bound to.
Benefits:
- Processing that is automated or semi-automated.
- Unbiased interpretation of the findings.
- Integrating with the computer system in the lab to enable the creation of electronic reports.
Western Blot Technique:
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Using the entire T. pallidum lysate antigen as a basis.
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It appears that acquired syphilis can be diagnosed by the presence of antibodies to the immunodeterminants with molecular weights of 15.5, 17, 44.5, and 47 kDa.
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The test is useful in the diagnosis of congenital syphilis when an IgM-specific conjugate is employed.
What Are the Non-treponemal Tests for Syphilis?
Syphilis is caused by the Treponema pallidum subspecies pallidum. Although congenital syphilis is typically spread through sexual contact, it can also be vertically transferred from mother to child during pregnancy or during the delivery process.
Untreated syphilis cases can end in multisystem involvement and severe morbidity, regardless of the mode of transmission. There are latency periods associated with systemic sickness. Diagnosis by serologic testing is the recommended approach. Treponemal and nontreponemal assays are the two types of serologic tests that are employed. A nontreponemal test is the first step in the traditional serologic screening process for syphilis, and reactive results are confirmed by a treponemal test. To validate reactive results, reverse screening algorithms start with a treponemal test and then move on to a nontreponemal test.
Conclusion
Every patient who is suspected of having syphilis should undergo a treponemal test (TPHA) after undergoing an NTT (qualitative VDRL). The VDRL test can be used to detect new infections and to track how well a treatment is working. Treponemal tests are more specific, but they do not show a recent infection because of the restriction that they stay positive for life.
