Properties of Treponema pallidum @ Treponema is a small, spirochaete measuring 6-15 x 0.2 μm. @ It has 6-12 coils. @ Not seen by light microscopy, Best seen by dark-field microscopy. @ It has bending & rotating motility. @ No culture. May survive in blood.
Treponema Antibodies: @ Non-specific autoantibody (cardiolipin) @ Specific treponemal antibody. Non-specific autoantibody (cardiolipin) @ Produced 2-3 weeks after infection @ It acts against patient damaged mitochondria . @ Detected in serum by cardiolipin Ag. Hence called cardiolipin antibody
@ Cardiolipin antibody is positive in: Syphilis Other treponemal conditions Pregnancy Autoimmune diseases Tuberculosis Leptospirosis Cancer Leprosy Malaria
Serological tests for Treponema: @ Used to diagnose syphilis, yaws, pinta @ There are two test groups: * Cardiolipin antigen tests. * Treponemal antigen tests. Cardiolipin antigen tests: @ VDRL test. @ RPR (rapid plasma reagin) test. @ Wassermann test: no longer used.
VDRL TEST: @ Only patient serum is used @ Serum is heated for 30 min. at 56°C @ Control sera must be included. @ Cardiolipin antigen is diluted. @ Result read microscopically from slide @ Technique is difficult @ Not very sensitive @ Few false positive results
RPR test: @ The antigen contains carbon or dye. @ Result is read by naked eye on a card @ Both plasma and serum are used. @ Antigen not diluted or heated @ Control sera must be included. @ Technique is easy @ Good sensitivity @ Many false positive results
Comparison of VDRL AND RPR Specimen Only serum used, serum heated Serum & plasma used, no heating Antigen Diluted before use Not diluted Reading of results Microscopically from slide Macroscopically from card Technique Difficult Easy Sensitivity Less sensitive More sensitive False positive Less often More often
Treponemal Antigen Tests: Three tests: @ TPHA-T.Pallidum Hemagglutination test @ FTA-ABS-Fluorescent Treponemal Antibody-ABSorption test. Recommended only in reference labs. @ TPI-Treponema Pallidum Immobilization test. Costly, difficult to perform, No longer used for diagnosis of syphilis
TPHA: @ It is cheap, simple, quick to perform, requires no special equipment. @ Antigen is derived from Nichol's strain of T.pallidum. @ It is coated on sheep RBC. @ Performed in microtitre plates to save reagent. @ Control sera must be included.
Interpretation of Serological Tests Condition RPR & VDRL TPHA & FTA-ABS Primary early syphilis Positive or negative Secondary early syphilis Positive Late and neurosyphilis Inactive & treated syphilis Negative or positive Congenital syphilis Active yaws or pinta Inactive yaws or pinta
CSF in neurosyphilis: @ RPR is not suitable for testing CSF. @ VDRL usually positive or 45% negative @ TPHA test is positive. Serum in neurosyphilis: @ TPHA is positive. @ RPR and VDRL are positive or negative