Treponema pallidum loads in biological samples associated with distinct syphilis outcomes

_ Abstract Syphilis is the sexually transmitted disease caused by Treponema pallidum, which presents distinct clinical manifestations posing different implications for diagnosis. Nevertheless, the inherent factors leading to diverse disease progressions are still unknown. We aimed to assess the association between treponemal loads and dissimilar disease outcomes, to better understand syphilis. We analyzed 309 DNA samples from distinct anatomic sites associated with particular syphilis manifestations. An absolute quantitative real-time PCR procedure was used to precisely quantify the number of treponemal and human cells to calculate T. pallidum loads in each sample. Exudates from primary lesions presented the highest T. pallidum loads in contrast with bloodderived samples. High dispersion of T. pallidum concentrations was observed in blood-derived samples from secondary syphilis. T. pallidum was detected in substantial amounts in 37 samples of seronegative individuals and in 13 cases considered as syphilis-treated. This study suggests a scenario where syphilis may be characterized by: i) heterogeneous and high treponemal loads in primary syphilis, reflecting dissimilar duration of chancres development and resolution; ii) potential replication capability of T. pallidum while in the bloodstream, suggested by high dispersion of bacterial concentrations in secondary syphilis cases; and iii) bacterial evasiveness, either to the host immune system or antibiotic treatment. _Introducao Treponema pallidum subsp. pallidum (T. pallidum) e a espiroqueta responsavel pela sifilis. Esta bacteria infeta o ser humano e transmite-se durante a gravidez da mae para o feto, por transfusao sanguinea mas, sobretudo, por contacto sexual, enquadrando-se, por isso, no âmbito das infecoes sexualmente transmissiveis (IST)