(P381) Detection of treponemal tp47 and tp0548 genes in oral, anal and genital lesion samples from syphilis patients

Background
Painless chancres are common symptoms of syphilis and are present in about one-third infected individuals; extra genital locations as well as hidden rectal or vaginal chancres could cause misdiagnosis. Treponema pallidum (TP) DNA detection based on polymerase chain reaction (PCR) assays is commonly performed in lesion samples using tp47 and polA genes, with sensitivities over 80%. We evaluated the performance of using two gene targets tp47 and tp0548 for TP DNA detection in anal, oral and lesion swabs samples from active syphilis cases.

Methods
Between 2019 and 2022, participants diagnosed with active syphilis using laboratory (rapid reagin plasmatic [RPR] of ≥1:8 and ≥2-fold titer increase from previous RPR) or clinical criteria (having syphilitic chancre) from STI clinics in Peru were enrolled in a cohort study. We collected samples three different types for TP DNA detection: oral mucosa, anal mucosa and urogenital lesions. Samples were collected and stored in a vial with 500ul lysis buffer. DNA was extracted by columns (Zymo research, USA) and assessed using specific primers for conventional PCR to amplify tp47 and tp0548 target genes. We calculated the proportion of TP DNA detected for each target in all oral, anal and lesion samples and compared the positivity by syphilis stage.

Results
Overall 258 oral, 116 anal, and 87 lesion swabs samples were collected. We detected tp47 and tp058 targets in 10/258 (3.9%) and 13/258 (5.0%) in oral swab specimens, respectively; tp47 and t0548 targets in 45/116 (38.8%) and 18/116 (15.5%) anal swab specimens, respectively; and tp47 and tp0548 in lesion swab samples 21/87 (24.1%) and 42/87 (48.3%), respectively. We detected tp47 in 34.6%, 50.0%, 18.7% and 21.7% cases of primary, secondary, early latent and late latent syphilis respectively. In addition, we detected tp0548 in 51.8%, 40.9%, 11.2% and 4.3% cases of primary, secondary, early latent, and late latent syphilis, respectively.

Conclusion
Using tp47 and tp0548 genes in combination improves the detection of TP DNA in different types of samples from patients with syphilis. Using both PCR targets for screening of anal and oral samples may facilitate detection of syphilis cases when genital lesions are absent.