The Laboratory Diagnosis Of Syphilis

The Laboratory Diagnosis Of Syphilis

Describe the morphology of the etiological agent and laboratory diagnosis of syphilis.
Answer:

Syphilis is a veneral disease caused by spirochetes, Treponema pallidum.

Etiological agent Morphology of Treponema Pallidum

T. pallidum is a coiled spiral filament that is 10 µm long

Laboratory diagnosis of syphilis

Etiological agent Laboratory Diagnosis

Syphilis is diagnosed in the laboratory either by demonstration of organism in the specimen by dark fild examination or by a serological test.

Dark Field Examination

Treponema pallidum may be found in the primary lesion or in mucous patches of secondary syphilis. Exudate taken from lesion is examined under dark field microscope. T. pallidum appears as delicate, tightly bound measuring 6 µ.

Serological Tests

They give positive results after 4 weeks of infection. So they are strongly positive in second stage and in congenital syphilis.

Syphilis produces two types of antibodies, i.e. specific Antitreponemal antibodies and non-special reagin antibodies which are measured by specific and non-specific tests.

Etiological agent Non-Specific

In these test, flocculation of antigen suspension occurs and is seen.

The VDRL Test

• Patients infected with T. pallidum produce a nonspecific antibody-like substance called reagin. When the VDRL antigen mixture made of cardiolipin, cholesterol and lecithin is reacted with serum containing regain visible reaction, flocculation, occurs.
• The test is reactive in 70-99% of primary and secondary syphilis cases but is usually non-active in tertiary cases.

The RPR Test

• The RPR test has a carbon-containing cardiolipin antigen that reacts with the antibody-like substance produced in response to syphilis and other conditions.
• This is also a flocculation test, with the carbon causing black clumps at the white background in a reactive test. Test results are reported as ‘reactive’ or ‘non-reactive.”
• A reactive result does not mean the patient definitely has syphilis; it only indicates the presence of time nonspecific antibodies.

Treponemal vs non-treponemal

Etiological agent Specific Test

• Hemagglutination test such as T. pallidum hemagglutination assay
• Fluorescent test such as florescent T. pallidum antibody absorption
• Immobilization test, i.e. Treponema pallidum immobilization.
• Treponemal ELISA test.

Etiological agent Other Test

Chest skiagram for calcification of aorta in cardiovascular syphilis

CSF examination in neurosyphilis.