Evaluation of treatment-related serological changes in Treponema pallidum subsp. endemicum infection using latex-based immunoassays, with comparison to Treponema pallidum subsp. pallidum

Background Treponema pallidum subsp. endemicum (TEN), the causative agent of bejel, is a nonvenereal treponematosis that occurs mainly in arid regions such as Africa and the Middle East. Recently, sexually transmitted TEN infections have been reported outside endemic regions, but their serological characteristics and treatment responses remain unclear. Methodology/principal findings We analyzed 6 genetically confirmed bejel patients and 9 syphilis patients in Japan. Serum treponemal (TP) and non-treponemal (RPR) antibody titers were quantified at baseline and post-treatment using latex agglutination test (LA). The analysis of antibody profiles was performed with an immunoblot assay detecting IgM and IgG antibodies against Tp47, TmpA, Tp17, and Tp15. Phylogenetic analysis based on concatenated tp0548 and tp0856 sequences identified 6 bejel cases (TEN). Changes in TP and RPR antibody titers following treatment showed no apparent difference between bejel and syphilis groups. In both groups, some IgM antibodies decreased following treatment, while some IgG antibodies increased. Conclusions/significance The serological profiles and post-treatment changes in antibody titers were similar between bejel patients and syphilis patients. These findings suggest that conventional serological assays developed for syphilis may also be useful for clinical management of bejel, including evaluation of treatment response. This study provides new insight into the diagnosis and serological monitoring of sexually transmitted bejel cases outside endemic areas.