Evaluation of a minimal array of Treponema pallidum antigens as biomarkers for syphilis diagnosis, infection staging, and response to treatment

Update on syphilis diagnostics

PURPOSE OF REVIEW

Syphilis is rising globally, with resultant increases in morbidity and mortality that disproportionately impact underserved populations. Appropriate screening and testing for syphilis with accurate, reliable, affordable, and timely assays is crucial for combating this epidemic. This review provides a brief overview of laboratory methods for syphilis diagnosis, with a focus on recent updates in diagnostics and directions for future research.

RECENT FINDINGS

Syphilis can be complex and time-consuming to diagnose and stage appropriately. The historic use of darkfield microscopy for diagnosis has been eclipsed by algorithms that include both nontreponemal and treponemal antibody tests for screening and confirmation of active Treponema pallidum infection. Newer diagnostic modalities include nucleic acid amplification assays (NAATs) and point-of-care testing (POCT), which hold promise for increasing identification of active syphilis but have notable limitations. More work is needed to develop accurate, reliable, affordable, and expeditious tests to optimize syphilis diagnosis.

SUMMARY

Algorithms utilizing a combination of serological treponemal and nontreponemal assays remain standard of care for the diagnosis of syphilis, but recently developed NAATs and POCT assays present opportunities to increase syphilis detection. Further research is warranted to improve upon these testing modalities and explore other markers that could aid in syphilis diagnosis.

The serological dilemma: rethinking syphilis treatment evaluation

INTRODUCTION

Nontreponemal tests (NTT) constitute a significant method in syphilis detection, playing a crucial role in screening, diagnosing, and monitoring disease activity. However, recent discussions have cast doubt on the traditional belief that NTT are suitable for evaluating treatment efficacy, as inconsistencies between NTT results and syphilis treatment outcomes have been observed with some frequency.

AREAS COVERED

We have delineated the current status of serological methods for evaluating the therapeutic efficacy of syphilis treatment and summarized and discussed the exploration of biomarkers for syphilis therapy. A literature search was conducted in PubMed over all available dates for relevant published papers and conference abstracts with the search terms, 'Syphilis,' 'Treponema pallidum,' 'Serofast,' 'Treatment efficacy evaluation,' 'Nontreponemal,' 'RPR,' 'TRUST,' 'VDRL,' 'Neurosyphilis,' 'Pregnant syphilis,' 'Congenital syphilis,' 'Reinfection,' 'Cardiolipin,' 'Serology.'

EXPERT OPINION

Currently, the assessment of treatment efficacy through serological methods is limited to the use of the NTT. Therefore, it is imperative for clinicians to gain a deeper understanding of the significance and limitations of the NTT, as well as a focus on exploring more potential indicators for evaluating treatment efficacy.

A novel pan-proteome array for high-throughput profiling of the humoral response to Treponema pallidum

Given the resurgence of syphilis, research endeavors to improve current assays for serological diagnosis and management of this disease are a priority. A proteome-scale platform for high-throughput profiling of the humoral response to Treponema pallidum (T. pallidum) proteins during infection could identify antigens suitable to ameliorate the performance and capabilities of treponemal tests for syphilis. Additionally, because infection-induced immunity is partially protective, profiling the response to T. pallidum outer membrane proteins (OMPs) could help select vaccine candidates. Therefore, we developed a pan-proteome array (PPA) based on the Nichols and SS14 strain complete proteomes and used it to define the immunoglobulin M (IgM) and IgG humoral response to T. pallidum proteins in sera collected longitudinally from long-term infected rabbits and from rabbits that were infected, treated, and re-infected. We identified antigens that could facilitate early diagnosis and immunity to a core set of OMP that could explain protection upon reinfection.

Neurosyphilis: insights into its pathogenesis, susceptibility, diagnosis, treatment, and prevention

Background and aim

Invasion of the central nervous system by Treponema pallidum can occur at any stage of syphilis. In the event that T. pallidum is not cleared promptly, certain individuals may experience progression to neurosyphilis, which manifests as cognitive and behavioral abnormalities, limb paralysis, and potentially fatal outcomes. Early identification or prevention of neurosyphilis is therefore crucial. The aim of this paper is to conduct a critical and narrative review of the latest information focusing exclusively to the pathogenesis and clinical management of neurosyphilis.

Methodology

To compile this review, we have conducted electronic literature searches from the PubMed database relating to neurosyphilis. Priority was given to studies published from the past 10 years (from 2013 to 2023) and other studies if they were of significant importance (from 1985 to 2012), including whole genome sequencing results, cell structure of T. pallidum, history of genotyping, and other related topics. These studies are classic or reflect a developmental process.

Results

Neurosyphilis has garnered global attention, yet susceptibility to and the pathogenesis of this condition remain under investigation. Cerebrospinal fluid examination plays an important role in the diagnosis of neurosyphilis, but lacks the gold standard. Intravenous aqueous crystalline penicillin G continues to be the recommended therapeutic approach for neurosyphilis. Considering its sustained prominence, it is imperative to develop novel public health tactics in order to manage the resurgence of neurosyphilis.

Conclusion

This review gives an updated narrative description of neurosyphilis with special emphasis on its pathogenesis, susceptibility, diagnosis, treatment, and prevention.