(P415) Clinical, microbiologic, and molecular epidemiology of early syphilis in Southwestern Colombia – implications for vaccine development

Background: Venereal syphilis, caused by the spirochete Treponema pallidum (TPA), is exploding worldwide, underscoring the need for a vaccine with global efficacy. Herein we analyzed the sociodemographic, clinical, and molecular features of the disease in Latin America, where transmission and genomic diversity of TPA has been grossly understudied.





Methods: We identified individuals in Cali, Colombia with a potential diagnosis of early syphilis (ES) through a city-wide network of public health centers, private sector HIV clinics and laboratory databases from public health institutions. Clinical, socio-demographic, and sexual histories were obtained. Whole blood (WB), skin biopsies (SB), and mucosal lesion swabs, when present, were obtained for measurement of treponemal burdens by polA qPCR and whole-genome sequencing (WGS). Isolation of TPA from WB by rabbit infectivity testing was attempted for 10 subjects.





Results: Among 1,966 individuals screened, 128 subjects met enrollment criteria: 112 (87%) with secondary (SS), 15 (12%) with primary (PS) and 1 with early latent syphilis. 66/128 (52%) self-reported to be heterosexual, while 48 (38%) were MSM; two-thirds were cis-gender men. 96% initiated sexual intercourse under the age of 20, 15% were commercial sex workers and 7% were forced migrants. 38% had HIV coinfection, 6.2% hepatitis B, 6.2% hepatitis C and 27% had a previous episode of syphilis. WB polA positivity was more common in SS than PS, with 42% and 7% positivity rates (PR) [Fisher’s exact p=0.009]. PS genital ulcer swabs had the highest polA copy numbers (67 copies/ml) with a PR of 73%, while SS lesions had 42 polA copies/ml with PR of 62%. RIT passage success was achieved in 5 (50%) of 10 WB samples tested. WGS revealed that SS14 was the predominant clade and had a greater number of sublineages than Nichols. One contemporary Nichols-lineage isolate belonged to a subclade otherwise comprised of historical laboratory strains. Half of all samples were resistant to azithromycin.





Conclusion: This study offers new insights into the sociodemographic and clinical features of venereal syphilis in Colombia. This first-of-its-kind TPA RIT and DNA WGS analysis in Latin America sets the stage for further research to identify, regionally relevant syphilis vaccinogens.