Diagnosis Of Syphilis: Serodiagnosis And Significance In Its Different Stages

Two types of serological tests have been developed; the nonspecific tests using cardiolipin from beef heart and specific tests using live or killed laboratory strains of treponemes or their components. The nonspecific tests are the Wasserman’s test. Kahn test, and the Veneral Disease Research Laboratory (VDRL) test. Among the specific tests, the commonly used ones are Treponema pallidum immobilization (TPI) test and the fluorescent treponemal antibody-absorption (FTA- ABS) test. There are several other tests used in different laboratories.

Interpretation of serological tests: The non specific serological tests becomes positive about 4 weeks after infection and the titre progressively increases in the secondary stage. If the disease is treated and cured at this stage, the titers fall and the test may become negative in 4 to 6 months. Treatment instituted late in the disease may not eliminate seropositively. False positive reactions not due to any technical error are known as biological false positive reactions. This may occur in connective tissue disorders like SLE and rheumatoid disease, malaria, leprosy, hepatitis, infectious mononucleosis, and tuberculosis.

The FTA-ABS test becomes positive early after infection. The TPI test becomes positive only later than the FTA-ABS. Once positive, they remain so for life. Early treatment in primary stage prevents the development of seropositivity. Reaginic tests are useful to determine cure since they decline in titer if the disease is treated sufficiently.

In the primary and secondary stages, diagnosis is established by demonstration of the organism by dark ground microscopy and serological tests. All genital ulcers should be investigated for syphilis irrespective of their appearance. Treatment should always be given only after an accurate diagnosis has been made. All suspected cases should be kept under observation for a minimum period of three months and serological tests for syphilis should be perfomed at regular intervals. All sexual contacts of the patient during the past six months should be traced and examined.

Latent Syphilis: Latent syphilis is diagnosed when the standard serological tests for syphilis are positive in the blood without any clinical evidence of the disease.

Late syphilis: It is essential to confirm the diagnosis by serological examination before starting the treatment. The cerebrospinal fluid should be examined in all cases of secondary syphilis to exclude meningeal involvement.

Congenital Syphilis: The disease should be suspected in children born to mothers who are syphilitic. In the early infectious state, diagnosis can be established by finding T. Pallidum on dark ground examination of the discharge from the lesions of the skin, mucous membrane and nasal discharge. Serological tests have to be interpreted with caution in the early weeks of life. Maternal reaginic antibodies of IgG class may be passively transferred across the placenta and these may lead to positive serology in the infant even though the baby is not suffering from syphilis. These disappear with time. If the baby is really affected, IgM antibodies develop and the rise in titers can be demonstrated by specific tests (IgM-FTA-ABS).