Treponema Pallidum: Diagnosis and Treatment
Diagnosis:
1.Demonstration of Organism
- Darkfield microscopic examination of lesion exudate such as chancre of primary syphilis
- Immunofluorescence or immunohistochemical method more reliable.
2. Serological tests for Syphilis:
- Serologic testing is considered the standard method of detection for all stages of syphilis.
(a) Non-treponemal tests
- RPR (Rapid plasma reagin)
- VDRL
VDRL principle:
- Heat-inactivated (to destroy complement) serum of patient is reacted with freshly prepared non-treponemal antigen
- Flocculation reaction (antigen and antibody complex are suspended) occurs.
- The flocculation can be observed by using microscope.
The sensitivity of the Non-treponemal tests like VDRL and RPR tests :
- 78-86% for detecting primary syphilis
- 100% for detecting secondary syphilis
- 95-98% for detecting tertiary syphilis.
- Specificity ranges from 85-99% .
Possibility of false-positive results in:
- Viral Hepatitis, SLE, and Leprosy.
(b)Treponemal test
- Confirmation of any positive or equivocal nontreponemal test result should follow with a treponemal test
- Fluorescent treponemal antibody-absorption (FTA-ABS)
- Microhemagglutination assay T pallidum (MHA-TP)
- T pallidum hemagglutination (TPHA)
- FTA-ABS-Confirmatory test
- TPI (Treponemal pallidum immobilization) test(most specific)
- Sensitivity of 84% for detecting primary syphilis infection
- 100% sensitivity for detecting syphilis infection in other stages
- Its specificity is 96%.
- Congenital syphilis can be best diagnosed by IgM FTA- ABS
- Ig M does not cross the placenta
- Its presence in neonatal serum confirms congenital syphilis.
- Capita M test and the 19S Ig M FTA-ABS test are available
Treatment of syphilis
- Primary or secondary syphilis –
- Benzathine penicillin G 2.4 million units intramuscularly (IM) in a single dose
- Early latent syphilis –
- Benzathine penicillin G 2.4 million units IM in a single dose
- Late latent syphilis or latent syphilis of unknown duration –
- Benzathine penicillin G 7.2 million units total, administered as 3 doses of 2.4 million units IM each at 1-week intervals
- Pregnancy – In patients with a history of penicillin allergy, skin testing is recommended.
- Treatment appropriate to the stage of syphilis is recommended.
Exam Important
- Treponema pallidum isolation from CSF is maximum in the secondary stage of syphilis.
- Infection leads to lifelong immunity.
- Penicillin is the only recommended agent for treatment of syphilis in pregnancy.
- If the patient has a documented penicillin allergy, desensitization and penicillin therapy should be given.
- Seropositive infant not treated at birth if mother received penicillin in 3rd trimester
- Biological False positive/ BFP serological test for syphilis may be encountered in: Primary or secondary syphilis – Benzathine penicillin G 2.4 million units intramuscularly (IM) in a single dose
- Viral Hepatitis, SLE, and Leprosy.
- Congenital syphilis can be best diagnosed by IgM FTA- ABS
- Most sensitive diagnosis during secondary stage of syphilis is VDRL.
Treponemal Test-
- Fluorescent treponemal antibody-absorption (FTA-ABS)
- Microhemagglutination assay T pallidum (MHA-TP)
- T pallidum hemagglutination (TPHA)
- FTA-ABS-Confirmatory test
- TPI (Treponemal pallidum immobilization) test(most specific)
- Non-treponemal tests
- RPR (Rapid plasma reagin)
- VDRL
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