Dark ground examination
Spirochaetes can be demonstrated by microscopic examination of smears from early lesions using dark ground or fluorescent antibody techniques. Antibiotics or antiseptics should not be used until satisfactory examination has been completed. Dark ground examination is not suitable for oral lesions.
Serological tests provide indirect evidence of infection. The non-specific reagin tests, namely the Venereal Disease Research Laboratory test (VDRL) and the Rapid Plasma Reagin test (RPR), are reactive in 50 to 75% of cases of primary syphilis and in most cases of secondary syphilis. The reagin tests are inexpensive and capable of automation. They are generally used for screening. Treponemal tests, including the Fluorescent Treponemal Antibody test (FTA-ABS) and the Treponema pallidum Haemagglutination Assay (TPHA), are more specific than the reagin tests (see table 2). In early syphilis, the FTA-ABS usually becomes positive first followed by the reagin tests and then TPHA. The reagin tests usually become negative within 3 to 6 months of effective treament. Treponemal tests may remain positive for years. False positive FTA-ABS tests have been reported in association with herpes infection.