Background Treponema pallidum subsp. pallidum (TPA) is the causative agent of syphilis, a world-wide prevalent venereal disease. Bejel is caused by T. pallidum subsp. endemicum (TEN), which shows similar clinical manifestations and is morphologically and serologically indistinguishable from TPA. The PCR used for syphilis diagnostics, targeting the polA gene, does not discriminate between subspecies of T. pallidum. Bejel is thought to be restricted to semi-arid areas and its transmission to be non-venereal, but recently, in patients diagnosed with syphilis in Cuba and Japan, sexual transmission of TEN was shown to occur. We therefore performed molecular typing on samples from Surinam, Antillean and Dutch patients to discover bejel causing TEN strains among syphilis cases in Amsterdam.

Methods DNA was extracted from 137 ulcer swabs collected between 2006 and 2018 from male clients attending the Amsterdam sexually transmitted infections (STI) clinic. MLST was performed by partial sequence analysis of the tp0136, tp0548 and tp0705 genes to generate allelic profiles. In addition, 23S rRNA loci were checked for A2058G and A2059G macrolide resistance mutations.

Results We found 15 distinct allelic profiles from 99/137 (72%) fully typed samples, of which none were TEN, 83% were SS14-like strains and 17% Nichols-like. The most prevalent types were 1-3-1 (44%) and 1-1-1 (19%), in concordance with similar TPA typing studies. There was no association found between TPA types and ethnicity. Five new allelic types and profiles were found adding to the knowledge of TPA strain diversity. The successfully sequenced 23S rRNA loci from 123/137 (90%) samples showed the presence of A2058G and A2059G mutations, 79% and 2% respectively.

Conclusion No misdiagnoses were found within the samples from different ethnicities residing in Amsterdam, the Netherlands. The strain diversity found in this study reflects the local male STI clinic population which is a diverse, mixed group.

Disclosure No significant relationships.