A 24 year old male presents to a STD clinic with a single painless ulcer on external genitalia. The choice of laboratory test to look for the etiological agent would be:

Ans. is 'c' i.e. Scrapings from ulcer for dark field microscopy [Ref.: Harrison 16/e p 981 (15 /e p. 1046, 1047)Single painless ulcer on external genitalia in young male is suggestive of syphilis the patient is in the first stage of syphilis. The single painless ulcer is primary chancre.Diagnosis of syphilisAbsolute diagnosis during the first and second stages can be made by direct examination under dark field microscopy of a specimen from infective lesions which arePrimary chancreMaculopapular rashCondyloma lataDarkfield microscopy reveals tiny helically shaped organisms moving in a corkscrew like fashion.Since direct visualization of spirochetes effective only during the active stages primary and secondary syphilis, serological tests were developed for diagnosis. These serologic tests detect antibodies IgM or IgA type against antigen.Let's seeApproach to diagnosis of Genital ulcers (also see the table from Q. No. 74 of May 2001)Painful ulcers* -Chancroid, HerpesPainless ulcers* -Syphilis, lymphogranulomaVenarum, DonovanosisUlcer with Necrotic base -Hemophilus DucreyiIndurated ulcers* -SyphilisVesicular lesions -HerpesMultiple ulcers -ChancroidHerpes (B/L symmetrical)Donovanosis (can be single or multiple)Single lesions* -Syphilis, LGVLymphadenopathy* -Present in all exceptDonovanosis (pseudobuboes* are seen)Painful lymphadenopathy* -Cancroid's LGVSinuses in lymphadenopathy* - Lymphadenopathy present after theLGVlesion has healed* -LGV