Syphilis, caused by Treponema pallidum subspecies pallidum (TP), is a complex multi-stage infectious disease. Systematic dissemination is known to occur within a few hours of transmission. We investigated the molecular variation of TP at various body locations within patients and assessed whether infections with multiple strains could be detected within one patient.
We included 293 men who have sex with men (MSM) suspected of syphilis at the sexually transmitted infections clinic in Amsterdam in 2018–2019; 70 (24%) had primary syphilis, 73 (25%) secondary syphilis, 86 (29%) early latent syphilis, 14 (5%) late latent syphilis and 50 (17%) did not have syphilis. Extra study samples were collected: peripheral blood, a pharyngeal and an anal swab, and a urine sample. TP-DNA was detected using a polA targeting qPCR. All positive TP samples, including ulcer swabs, were characterized using multi-locus sequence typing (TP-MLST) based on sequence analysis of three genetic regions (tp0136, tp0548, tp0705).
Full TP-MLST types were obtained for the following TP-DNA positive samples: 1/22 (5%) peripheral blood, 35/75 (47%) pharynx, 10/61 (16%) anus, 23/56 (41%) urine and 50/73 (68%) ulcer. At least one TP-MLST full type was obtained from 48/70 (69%) patients in the primary, 35/73 (48%) in secondary and 10/86 (12%) in early latent stage. For all 22 patients with ≥2 TP-MLST types, the TP-MLST type was identical at the different body locations. The most prevalent TP-MLST types were 1.3.1 and 1.1.1, detected in 39/93 (42%) and 17/93 (18%) patients. Five new tp0548 and 2 new tp0136 variants were found, resulting in 6 new TP allelic profiles.
The intra-patient TP homogeneity suggests that the TP-DNA detected at the different body locations occurs from dissemination rather than from different infections from multiple partners. The TP strain diversity is similar to that in previous TP-MLST studies among MSM in Amsterdam, the Netherlands.
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