Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2025 Jul 8;20(7):e0325073.
doi: 10.1371/journal.pone.0325073. eCollection 2025.

Treponema pallidum infection in asymptomatic persons: A puzzling scenario in the Canary Islands (Spain) (2001-2020)

Jose Luis Pérez-Arellano  1 , Araceli Hernández Betancor  2 , Oscar Sanz Peláez  3   4 , Jose Curbelo  5 , Michele Hernández Cabrera  3   6 , Elena Pisos Álamo  3   6 , Nieves Jaén Sánchez  3   6 , Laura Suárez Hormiga  3   6 , Carmen Lavilla Salgado  3   6 , Laura López Delgado  3   6 , Sandra González Linares  7 , Cristina Carranza-Rodríguez  1   8
Affiliations

Treponema pallidum infection in asymptomatic persons: A puzzling scenario in the Canary Islands (Spain) (2001-2020)

Jose Luis Pérez-Arellano et al. PLoS One. .

Abstract

Background and objectives: Syphilis is an infectious disease caused by T. pallidum subsp. Pallidum. In high-income countries the main mode of transmission is sexual. Approximately half of infected patients are asymptomatic, which does not exclude the possibility of transmission. The aim of this study was to evaluate syphilis seroprevalence among asymptomatic persons in Gran Canaria (Canary Islands, Spain).

Patients and methods: Three different groups were studied from 2001 to 2020: i) a "blood donor" sample of 948,869 voluntary blood donations as a proxy of health population.; ii) undocumented African immigrants, including 1,873 recent arrivals in Gran Canaria; and iii) people living with HIV (PLWH), a group of 1,690 patients followed by our team. The evaluation included both treponemal and reaginic tests.

Results: i) among blood donors, the mean seroprevalence of positive treponemal tests was 0.25% (95% CI: 0.19-0.31). Non-treponemal test positivity (RPR) ranged from 0.05 to 0.06% with titers ≤ 1:4 in all cases; ii) thirty-four of 641 undocumented African migrants (5.30%; 95% CI: 3.82-7.32%) had a confirmed positive treponemal test but only 4 had a positive RPR, with titers ranging from 1:1-1:4; iii) 46.51% (95% CI: 44.14-48.89) of PLWH patients had a confirmed positive treponemal test. For factors related to HIV-syphilis coinfection, multivariate analysis clearly showed the association with male sex and the MSM risk category. However, the results of this series call into question the overall role of immigration in the seroprevalence of syphilis among PLWH in our setting. Active syphilis (RPR > 1:8) was found in 20.10% of PLWH.

Conclusions: In summary, syphilis is a re-emerging infection, and asymptomatic persons constitute a group that facilitates its transmission and spread. In our setting, seroprevalence was lowest in blood donors, higher in recently arrived African migrants, and highest in PLWH, especially MSM. The presence of active syphilis however is mainly restricted to MSM. This information is of relevance for the design of syphilis control strategies.

PubMed Disclaimer

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Positive treponemal test percentage in the study groups.
Each point indicates the percentage according to the year of study.
Fig 2
Fig 2. Seroprevalence of syphilis in the different groups (Gran Canaria) N (number of positive treponemal test)/ n (number of total group).
See this image and copyright information in PMC

Similar articles

See all similar articles

References

    1. Peeling RW, Mabey D, Chen X-S, Garcia PJ. Syphilis. Lancet. 2023;402(10398):336–46. doi: 10.1016/S0140-6736(22)02348-0 - DOI - PubMed
    1. Hook EW 3rd. Syphilis. Lancet. 2017;389(10078):1550–7. doi: 10.1016/S0140-6736(16)32411-4 - DOI - PubMed
    1. Arando Lasagabaster M, Otero Guerra L. Syphilis. Enferm Infecc Microbiol Clin (Engl Ed). 2019;37(6):398–404. doi: 10.1016/j.eimc.2018.12.009 - DOI - PubMed
    1. Rothschild BM. History of syphilis. Clin Infect Dis. 2005;40(10):1454–63. doi: 10.1086/429626 - DOI - PubMed
    1. Del Romero J, Moreno Guillén S, Rodríguez-Artalejo FJ, Ruiz-Galiana J, Cantón R, De Lucas Ramos P, et al. Sexually transmitted infections in Spain: current status. Rev Esp Quimioter. 2023;36(5):444–65. doi: 10.37201/req/038.2023 - DOI - PMC - PubMed