Spirochaetes can be identified by : March 2005
Correct Answer: Dark field microscopy
Description: Ans. D: Dark field microscopy Laboratory examinations for syphilis: In its primary and secondary stages, syphilis can often be diagnosed by dark-field examination of fresh exudate obtained from lesions. Because the exudates from non-syphilitic lesions may also contain spiral organisms, the result must be interpreted with care.T. pallidum may also be identified by immunfluorescent staining. Dark field microscopy is paicularly impoant in suspected early primary syphilis before serological tests become reactive. Specimens from genital ulcers or other lesions consistent with a chancre and from skin lesions of secondary syphilis, especially condylomata lata should be examined by dark field microscopy. Flocculation tests for Wasserman Abs are of great value in the presumptive diagnosis/ screening of syphilis or quantitation of syphilis antibody. The Wasserman antigen is a phospholipid known as cardiolipin which is a normal constituent of host tissue. The standard is the VDRL test. The RPR (Rapid Plasma Reagin) test is another widely used test. However, a wide variety of other diseases e.g. malaria, SLE, leprosy, and other infections may give a false-positive result. Wasserman antibody is usually detected 1 to 3 weeks after the primary lesion appears and reaches a maximum during the second stage of infection. Subsequently, this antibody may remain at an elevated level. However, it is only positive in 71% of patients with teiary syphilis and thus a negative VDRL test does not exclude late syphilis. Tests for treponemal antibody, such as the TPI (T. pallidum immobilisation) test, are more specific but are not generally available. The more widely performed fluorescent antibody (FTA) test is positive in 84% of patients with primary syphilis and in almost all patients with secondary or latent syphilis and 96% in teiary syphilis. It should therefore not be used as a screening test. The TPHA test is similar to the FTA test in its sensitivity and specificity. Antitreponemal antibodies decline more slowly than Wasserman antibody after treatment, and positive reactions may persist for years
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