Cerebrospinal fluid human immunodeficiency virus viral load in patients with neurosyphilis

Cerebrospinal Fluid Biomarkers of Symptomatic Neurosyphilis in People With HIV Compared with Uninfected Individuals

We evaluated the diagnostic clinical performance characteristics (DCPC) of cerebrospinal fluid (CSF) total protein (TP), white blood cell count (WBC), and lactate (LA) with different cutoff points as adjunct biomarkers of confirmed or presumptive symptomatic neurosyphilis (NS) and the impact of HIV infection. From 5,640 participants who underwent lumbar punctures, 236 participants were included, and classified as either people with HIV (PWH) or people without HIV (PWoH) according to the CDC criteria for confirmed NS (n = 42), presumptive NS (n = 74), systemic syphilis (SS) (n = 38), serological diagnosis of syphilis (n = 18), PWH without SS and NS (n = 10), and negative control (n = 72). In PWoH, for presumptive NS, the combination of CSF TP > 45 mg/dL and/or WBC > 5.0 cells/mm3 is valuable for screening, whereas in PWH, it is not recommended for either screening or case-finding NS, however the DCPC were better in the suppressed group. In PWoH, the value of CSF TP > 45 mg/dL is adequate for both screening and confirmation of presumptive NS, subject to prevalence. For WBC count > 20 cell/mm3, the positive predictive value (PPV) of the test is almost perfect, suggesting a confirmatory test. In PWH, CSF TP is an inadequate marker of NS. The WBC count, with cutoffs of > 10 or > 20 cells/mm3, was moderately applicable for screening.As conclusions: CSF WBC count and TP showed distinct DCPC in confirmed or presumptive NS, better in the former. These biomarkers could be included for presumptive NS diagnosis. DCPC of these biomarkers for the diagnosis of NS is greatly affected by HIV co-infection.

Performance of the nontreponemal tests and treponemal tests on cerebrospinal fluid for the diagnosis of neurosyphilis: A meta-analysis

Background

Nontreponemal and treponemal tests for analyzing cerebrospinal fluid to confirm the existence of neurosyphilis have been widely used, so we aim to evaluate and compare their performance on the cerebrospinal fluid in the diagnosis of neurosyphilis.

Methods

We conducted a systematic literature search on five databases and utilized a bivariate random-effects model to perform the quantitative synthesis.

Results

Nontreponemal tests demonstrated a pooled sensitivity of 0.77 (95% CI: 0.68-0.83), a pooled specificity of 0.99 (95% CI: 0.97-1.00), and a summary AUC of 0.97 (95% CI: 0.95-0.98). The pooled sensitivity, pooled specificity, and summary AUC of treponemal tests were 0.95 (95% CI: 0.90-0.98), 0.85 (95% CI: 0.67-0.94), and 0.97 (95% CI: 0.95-0.98), respectively. The pooled specificity of all nontreponemal tests varied minimally (ranging from 0.97 to 0.99), with TRUST (0.83) having a higher pooled sensitivity than VDRL (0.77) and RPR (0.73). Among all treponemal tests, EIA has outstanding diagnostic performance with a pooled sensitivity of 0.99 and a pooled specificity of 0.98.

Conclusion

Nontreponemal tests exhibited a higher pooled specificity, and treponemal tests exhibited a higher pooled sensitivity in diagnosing neurosyphilis on cerebrospinal fluid. TRUST may be a satisfactory substitute for VDRL. EIA is a prospective diagnostic tool that deserves further study in the future. Our study may be useful to clinical laboratories in selecting appropriate serological tests on the cerebrospinal fluid for the diagnosis of neurosyphilis.

Clinical characteristics, diagnosis, and predictors of neurosyphilis patients with human immunodeficiency virus co-infection: A retrospective study at infectious diseases hospitals in two cities of China

ABSTRACT

This study aimed to compare between the clinical and laboratory characteristics of neurosyphilis and those of syphilis in human immunodeficiency virus (HIV) positive and explore the risk factors associated with the occurrence of neurosyphilis in the HIV infected.In-patients diagnosed with HIV and syphilis co-infection who underwent a lumbar puncture and completed cerebrospinal fluid (CSF) examination were divided into neurosyphilis group and syphilis group. The demographic characteristics, symptoms and signs, and laboratory tests of the 2 groups were comparatively analyzed. Logistic regression analysis was used to explore the risk factors associated with the occurrence of neurosyphilis.Among 81 patients, 33 patients were assigned to the neurosyphilis group, and 48 to the syphilis group. There were no significant differences in the age, gender, marital status, acquired immunodeficiency syndrome course, opportunistic infections, serum HIV viral load, and history of syphilis treatment. The difference in HIV transmission route between the 2 groups was statistically significant (P = .010), and the patients from the neurosyphilis group were mainly infected via heterosexual contact. The proportion of serum toludine red unheated serum test (TRUST) titer ≥1:16 in the neurosyphilis group were 78.8%, which was significantly higher compared to the syphilis group (48.9%). The level of CSF white blood cell count, CSF protein, and CSF HIV viral load in the neurosyphilis group were significantly higher than those of the syphilis group. The proportion of patients with neurological symptoms and signs in the neurosyphilis group was significantly higher compared to the syphilis group (P < .001). Multivariate logistic regression analysis showed that heterosexual contact transmission route, not received antiretroviral therapy, lower CD4 cell count and higher serum TRUST titer, untreated with syphilis, and neurological symptoms and signs were risk factors associated with the occurrence of neurosyphilis.The serum TRUST titer, CSF white blood cell count, CSF protein level, CSF HIV viral load, and the percentage of neurological symptoms and signs in the neurosyphilis group were higher. Heterosexual transmission route, not received antiretroviral therapy, and untreated with syphilis prompted the possibility of neurosyphilis occurrence.

Hepatitis B, Hepatitis C, tuberculosis and sexually-transmitted infections among HIV positive patients in Kazakhstan

In contrast with global trends, HIV prevalence in Kazakhstan and other Central Asian countries has been rising in recent years. In this study, we analyzed hepatitis B (HBV), hepatitis C (HCV), tuberculosis (TB) and sexually-transmitted (STI) co-infections among 500 HIV positive study participants recruited from all regions of Kazakhstan. Among our study participants, 27%, 8%, 2%, and 5% were coinfected with, respectively, HCV, TB, HBV, and STI. A considerable proportion of the study participants was also found with triple or quadruple infections of HCV/TB (12%), TB/STI (0.8%), HCV/STI (2%), HCV/HBV (1%), HBV/TB (0.4%), HBV/STI (0.2%), HBV/HCV/TB (0.4%), HBV/HCV/STI (0.2%), or HCV/TB/STI (0.2%). Strong associations were found of certain age groups, duration of HIV infection, and practices of injection drug use and sexual contact with PLWH, with co-infections of HIV/HCV and HIV/TB. The odds of having death was 4.07 times higher with TB/HIV as compared to other co-infections. Co-occurrence of HIV with HCV, HBV, and TB infections among participants of this study highlights the necessity of regular screening for HCV infection among HIV infected patients, together with implementation of vigilant vaccination protocols against HBV and TB. Additionally, persons who inject drugs especially need to be focused for harm reduction efforts that include opiate substitution therapy, needle or syringe exchange programs, regular screening, and increased availability of ART and direct acting antivirals.

Symptomatic cerebrospinal fluid escape

: Cerebrospinal fluid (CSF) viral escape is defined by detectable HIV-RNA in CSF despite undetectable or lower-than-CSF level in plasma of patients receiving combination antiretroviral therapy (cART). This condition may occasionally be associated with neurological problems, consisting of new and progressive cognitive decline and/or focal symptoms and signs, defining the 'symptomatic CSF escape'. Brain MRI usually shows diffuse white matter hyperintensities that recall the presentation of HIV encephalopathy in the precART era. However, patients develop symptomatic CSF escape with relatively high CD4 cell counts and suppressed or low systemic virus replication. In addition, the frequent CSF pleocytosis and the pathological demonstration of CD8 T-cell brain infiltrates in some cases of symptomatic escape indicate that inflammation is an important component in the pathogenesis of this condition. Low nadir CD4 cells are common, likely reflecting the establishment of a HIV reservoir in the central nervous system (CNS). CSF escape seems to result from reactivation of CNS infection when cART potency is lowered, because of low patient's adherence, drug resistance, or use of drug combinations that are poorly effective in the CNS and cART optimization is key to revert escape and neurological disease in the great majority of cases.

Prevalence and risk factors of syphilis and human immunodeficiency virus co-infection at a university hospital in Brazil

INTRODUCTION

The incidence of syphilis has increased since the 1970s.

METHODS

This was a descriptive and analytical cross-sectional study with a non-probabilistic sample.

RESULTS

Of 973 patients with human immunodeficiency virus, 179 (18.4%) tested positive for both human immunodeficiency virus and syphilis, 84.8% were men, 50.9% were aged between 36 and 50 years, 47.8% with syphilis were diagnosed with human immunodeficiency virus for 10-20 years, and 40.3% received antiretroviral therapy for 10-20 years.

CONCLUSIONS

The prevalence of syphilis in patients with human immunodeficiency virus is higher than expected, making it urgent to adopt efficient public health measures.

Neurosyphilis Increases Human Immunodeficiency Virus (HIV)-associated Central Nervous System Inflammation but Does Not Explain Cognitive Impairment in HIV-infected Individuals With Syphilis

Background

Individuals infected with human immunodeficiency virus (HIV) who have previously had syphilis may have cognitive impairment. We tested the hypothesis that neurosyphilis causes cognitive impairment in HIV by amplifying HIV-related central nervous system (CNS) inflammation.

Methods

HIV-infected participants enrolled in a study of cerebrospinal fluid (CSF) abnormalities in syphilis underwent the mental alternation test (MAT), venipuncture, and lumbar puncture. CSF concentrations of chemokine (C-X-C motif) ligand 10 (CXCL10), chemokine (C-C motif) ligand 2 (CCL2), and neurofilament light (NFL) were determined by commercial assays. The proportion of peripheral blood mononuclear cells (PBMCs) and of CSF white blood cells (WBCs) that were activated monocytes (CD14+CD16+) was determined by flow cytometry. Neurosyphilis was defined as detection of Treponema pallidum 16S RNA in CSF or CSF white blood cells (WBCs) >20/uL or a reactive CSF-Venereal Disease Research Laboratory (VDRL) test; uncomplicated syphilis was defined as undetectable CSF T. pallidum, CSF WBCs ≤5/uL and nonreactive CSF-VDRL. MAT <18 was considered low.

Results

Median proportion of PBMCs that were activated monocytes (16.6 vs. 5.3), and median CSF CXCL10 (10658 vs. 2530 units), CCL2 (519 vs. 337 units) and HIV RNA (727 vs. 50 c/mL) were higher in neurosyphilis than in uncomplicated syphilis (P ≤ .001 for all comparisons). Neurosyphilis was not related to low MAT scores. Participants with low MAT scores had higher median CSF CXCL10 (10299 vs. 3650 units, P = .008) and CCL2 (519 vs. 365 units, P = .04) concentrations than those with high MAT scores.

Conclusions

Neurosyphilis may augment HIV-associated CNS inflammation, but it does not explain cognitive impairment in HIV-infected individuals with syphilis.

Human Immunodeficiency Virus in the Brain-Culprit or Facilitator?

Introduction:

Human immunodeficiency virus (HIV) enters the brain early, where it can persist, evolve, and become compartmentalized. Central nervous system (CNS) disease can be attributed to HIV alone or to the complex interplay between the virus and other neurotropic pathogens.

Aim:

The current review aims to describe the direct impact of HIV on the brain as well as its relationship with other pathogens from a practitioner’s perspective, to provide a general clinical overview, brief workup, and, whenever possible, treatment guidance.

Methods:

A review of PubMed was conducted to identify studies on neuropathogenesis of HIV in relation to host responses. Furthermore, the interaction between the CNS pathogens and the host damage responses were revised in the setting of advanced and also well-controlled HIV infection.

Results:

Similar to other pathogens, HIV leads to CNS immune activation, inflammation, and viral persistence. Therefore, almost half of the infected individuals present with neurocognitive disorders, albeit mild. Compartmentalized HIV in the CNS can be responsible in a minority of cases for the dramatic presentation of symptomatic HIV escape. Disruption of the immune system secondary to HIV may reactivate latent infections or allow new pathogens to enter the CNS. Opportunistic infections with an inflammatory component are associated with elevated HIV loads in the cerebrospinal fluid and also with greater cognitive impairment. The inflammatory immune reconstitution syndrome associated with CNS opportunistic infections can be a life-threatening condition, which needs to be recognized and managed by efficiently controlling the pathogen burden and timely balanced combination antiretroviral therapy. Latent neurotropic pathogens can reactivate in the brain and mimic HIV-associated severe neurological diseases or contribute to neurocognitive impairment in the setting of stable HIV infection.

Conclusions:

As HIV can be responsible for considerable brain damage directly or by facilitating other pathogens, more effort is needed to recognize and manage HIV-associated CNS disorders and to eventually target HIV eradication from the brain.

Cerebrospinal Fluid HIV Escape from Antiretroviral Therapy

CNS infection is a nearly constant facet of systemic CNS infection and is generally well controlled by suppressive systemic antiretroviral therapy (ART). However, there are instances when HIV can be detected in the cerebrospinal fluid (CSF) despite suppression of plasma viruses below the clinical limits of measurement. We review three types of CSF viral escape: asymptomatic, neuro-symptomatic, and secondary. The first, asymptomatic CSF escape, is seemingly benign and characterized by lack of discernable neurological deterioration or subsequent CNS disease progression. Neuro-symptomatic CSF escape is an uncommon, but important, entity characterized by new or progressive CNS disease that is critical to recognize clinically because of its management implications. Finally, secondary CSF escape, which may be even more uncommon, is defined by an increase of CSF HIV replication in association with a concomitant non-HIV infection, as a consequence of the local inflammatory response. Understanding these CSF escape settings not only is important for clinical diagnosis and management but also may provide insight into the CNS HIV reservoir.

Incidence of Co-Infections of HIV, Herpes Simplex Virus Type 2 and Syphilis in a Large Cohort of Men Who Have Sex with Men in Beijing, China

BACKGROUND

The HIV-epidemic among MSM in China has worsened. In this key population, prevalence of HSV-2 and syphilis infection and co-infection with HIV is high.

METHODS

A longitudinal study was conducted (n = 962) in Beijing, China, with three overlapping cohorts (n = 857, 757 and 760) consisting of MSM that were free from pairs of infections of concern (i.e. HIV-HSV-2, HIV-syphilis, HSV-2-syphilis) at baseline to estimate incidence of HIV, HSV-2, syphilis, and those of co-infection.

RESULTS

The incidence of HIV, HSV-2 and syphilis in the overall cohort was 3.90 (95% CI = 2.37, 5.43), 7.87 (95% CI = 5.74, 10.00) and 6.06 (95% CI = 4.18, 7.94) cases per 100 person-years (PYs), respectively. The incidence of HIV-HSV-2, HIV-Syphilis and HSV-2-Syphilis co-infections was 0.30 (95% CI = 0.29, 0.88), 1.02 (95% CI = 0.13, 2.17) and 1.41 (95% CI: 0.04, 2.78) cases per 100 PYs, respectively, in the three sub-cohorts constructed for this study.

CONCLUSIONS

The incidence of HIV, HSV-2 and syphilis was very high and those of their co-infections were relatively high. Such co-infections have negative impacts on the HIV/STI epidemics. Prevention practices need to take such co-infections into account.

Cerebrospinal fluid analysis in the HIV infection and compartmentalization of HIV in the central nervous system

The nervous system plays an important role in HIV infection. The purpose of this review is to discuss the indications for cerebrospinal fluid (CSF) analysis in HIV infection in clinical practice. CSF analysis in HIV infection is indicated for the diagnosis of opportunistic infections and co-infections, diagnosis of meningitis caused by HIV, quantification of HIV viral load, and analysis of CNS HIV compartmentalization. Although several CSF biomarkers have been investigated, none are clinically applicable. The capacity of HIV to generate genetic diversity, in association with the constitutional characteristics of the CNS, facilitates the generation of HIV quasispecies in the CNS that are distinct from HIV in the systemic circulation. CSF analysis has a well-defined and valuable role in the diagnosis of CNS infections in HIV/AIDS patients. Further research is necessary to establish a clinically applicable biomarker for the diagnosis of HIV-associated neurocognitive disorders.

Neuroretinal Degeneration in HIV Patients Without Opportunistic Ocular Infections in the cART Era

Subtle structural and functional retinal abnormalities, termed 'HIV-associated Neuroretinal Disorder (HIV-NRD)', have been reported in HIV patients receiving combination antiretroviral therapy (cART), without infectious retinitis or any apparent fundus abnormalities otherwise. In this review, we provide an overview of studies investigating HIV-NRD in HIV patients without opportunistic ocular infections in the cART era, and try to elucidate underlying mechanisms and associated risk factors. Most studies focused on patients with severe immune-deficiency and demonstrated that patients with nadir CD4 counts<100 cells/μL are most at risk for neuroretinal damage, with a thinner retinal nerve fiber layer, subtle loss of color vision and/or contrast sensitivity, visual field deficits, and subnormal electrophysiological responses. In contrast, alterations in retinal vascular calibers and retinal blood flow were not associated with nadir CD4 counts, but instead with detectable viremia, suggesting a role for (chronic) inflammation in microvascular damage. Although the alterations in visual function are subtle, they can lead to difficulties in activities, such as reading or driving, thereby affecting quality of life. Since HIV has become a chronic disease, its long-term effects with respect to visual function loss become more important, as is recently emphasized by a longitudinal study, reporting that AIDS patients with HIV-NRD have higher risks of developing bilateral visual impairment and even blindness than patients without HIV-NRD. The question remains whether patients with high (>350 cells/μL) nadir CD4 counts and well-suppressed HIV infection on cART remain at risk for HIV-NRD, as this group constitutes a growing part of the aging HIV-infected population.

High frequency of neurosyphilis in HIV-positive patients diagnosed with early syphilis

BACKGROUND

Syphilis is an infection frequently seen with HIV, and European guidelines on the management of syphilis suggest that HIV-infected patients may have an increased risk of early neurological involvement, sometimes asymptomatic. Recent study shows a relationship between neurosyphilis and cerebrospinal fluid (CSF) HIV viral load (VL), which in turn may be associated with subsequent neurocognitive decline.

OBJECTIVES AND METHODS

The aim of the study was estimation of the frequency of neurosyphilis among HIV-positive patients with early syphilis. The study included all patients diagnosed with early syphilis who had lumbar puncture performed in the years 2008-2012. Analysis included CSF parameters (serology, mononuclear cells, protein, glucose, chloride and lactate levels), CD4 count, serum VL and highly active antiretroviral therapy (HAART). Diagnosis of neurosyphilis was confirmed by CSF serology [positive fluorescent treponemal antibody and/or Venereal Disease Research Laboratory (VDRL) test(s)] and increased number of mononuclear cells. Statistical analysis included χ(2) tests with an accepted significance level of P < 0.05.

RESULTS

Lumbar puncture was performed in 72 patients, all men, with median age 33 (interquartile range 11) years. Neurosyphilis was confirmed in 65 (90.28%) of the patients. No statistically significant association between CSF parameters and CD4 count was found. However, statistically significant associations were found only between pleocytosis and serum VL > 1000 HIV-1 RNA copies/mL (P = 0.0451), as well as HAART treatment (P = 0.0328). The proportion of confirmed neurosyphilis cases, also in patients with low serum VDRL titres, was very high.

CONCLUSIONS

Considering the high proportion of patients who objected to having LP performed in the absence of neurological symptoms and the risk associated with this procedure, it may be preferable to use treatments with good CNS penetration in all HIV-positive patients with early syphilis.

Neurosyphilis and the impact of HIV infection

Neurosyphilis is a complication of systemic syphilis. This review of the clinical presentation, diagnostic laboratory findings, treatment and management of neurosyphilis discusses the impact of HIV and the specific challenges it brings, focusing on areas of controversy, and highlighting important questions that remain to be answered.

Psychosis in neurosyphilis -- clinical aspects and implications

BACKGROUND

The World Health Organization estimates that 10-12 million new syphilis infections occur each year. Without treatment, years to decades after initial infection, 30% of affected individuals may develop tertiary syphilis, which can manifest as neurosyphilis. The aim of this review is to evaluate the research literature examining the psychopathological manifestations of psychosis in association with neurosyphilis.

METHOD

The authors performed a systematic electronic search for published studies (1995-2012). The following databases were used: Medline, Embase and the Cochrane Library as well as the search engines Scopus and Google Scholar.

RESULTS

61 articles were used for detailed analysis. Psychotic symptoms due to neurosyphilis are numerous and can inform differential diagnosis for many psychotic manifestations according to ICD-10 or DSM-IV.

CONCLUSION

Due to our results, current epidemiological data, and the difficulties in differential diagnosis of neurosyphilis, routine screening tests are still recommended in the psychiatric field. Long-term psychiatric input, with periodic syphilis titre controls, seems indicated in individuals affected by neurosyphilis with psychiatric symptoms. Furthermore, individuals with mental health problems may be at higher risk of acquiring syphilis.

Neurosyphilis: epidemiology, pathogenesis, clinical course and laboratory diagnostics

The article describes the key achievements and problems related to studying neurosyphilis. It also shows the dynamics of neurosyphilis incidence in Russia and abroad from the early twentieth century and up to present. The article also describes issues related to the pathogenesis, clinical course and pathomorphism of the disease. The authors present current approaches to the laboratory diagnostics of neurosyphilis.

Neurocognitive impairment in HIV-infected individuals with previous syphilis

Cognitive impairment is common in HIV-infected individuals, as is syphilis. Treponema pallidum, the bacterium that causes syphilis, invades the central nervous system early in disease. We hypothesized that HIV-infected patients with a history of syphilis or neurosyphilis would have more cognitive impairment than HIV-infected individuals without these infections. Eighty-two of 1574 enrollees in CHARTER, a prospective, observational study, had reactive serum rapid plasma reagin (RPR) tests. They were matched to 84 controls with non-reactive RPR by age, gender, ethnicity and HIV risk factor. Participants underwent comprehensive neuropsychological (NP) evaluations. RPR results were confirmed and serum fluorescent treponemal antibody absorption (FTA-ABS) test reactivity determined at a central laboratory. Sera from 101 of 166 participants were FTA-ABS reactive, indicating past or current syphilis. Among the 136 individuals without confounding conditions, compared with patients who had never had syphilis, those with prior syphilis had a greater number of impaired NP test domains (1.90 SD [1.77] versus 1.25 [1.52], P = 0.03), a higher global deficit score (0.47 [0.46] versus 0.31 [0.33], P = 0.03), and more were impaired in the NP learning domain (36 [42.9%] of 84 versus 13 [25.0%] of 52, P = 0.04). These effects of prior syphilis remained after controlling for education and premorbid intelligence.

Factors associated with cerebrospinal fluid HIV RNA in HIV infected subjects undergoing lumbar puncture examination in a clinical setting

BACKGROUND

Cerebrospinal fluid (CSF) HIV RNA load may be associated with central nervous system (CNS) disease in HIV infected subjects. We investigated parameters associated with CSF HIV RNA within a large clinical cohort.

METHODS

All HIV infected subjects undergoing CSF examination including assessment of CSF HIV RNA at St. Mary's Hospital, London, UK between January 2008 and October 2010 were included. Parameters associated with a detectable CSF HIV RNA load were assessed using linear regression modelling. CSF viral escape was defined as CSF RNA >0.5 log(10) copies/mL greater than plasma HIV RNA and >200 copies/mL where plasma HIV RNA <50 copies/mL.

RESULTS

Of 142 subjects, 99 were receiving antiretroviral therapy (ART). Plasma HIV RNA was <50 copies/mL in 69 subjects. CSF examination was performed for investigation of presumed HIV encephalopathy (IxHE, n = 57), other CNS diseases considered HIV related (n = 39), syphilis (n = 20) and CNS presentations not considered HIV related (n = 26). CSF viral escape was present in 30/142 (21%) subjects overall and in 9/69 (13%) of those on ART with undetectable plasma HIV RNA. Overall, plasma HIV RNA load was significantly associated with detectable CSF HIV RNA (p ≤ 0.001). In subjects with plasma HIV RNA <50 copies/mL, only CNS penetration effectiveness (CPE, 2008) score of <2 was significantly associated with detectable CSF HIV RNA (p = 0.044). In patients undergoing LP for IxHE both plasma HIV RNA and CPE scores were independently associated with detectable CSF HIV RNA (p = 0.019 & 0.003 respectively) which was not observed in subjects undergoing CSF examination for other medical reasons.

CONCLUSIONS

In a clinical setting, CSF viral escape is observed frequently in 21% of subjects and is associated with different parameters depending on the clinical scenario.

Syphilis: using modern approaches to understand an old disease

Syphilis is a fascinating and perplexing infection, with protean clinical manifestations and both diagnostic and management ambiguities. Treponema pallidum subsp. pallidum, the agent of syphilis, is challenging to study in part because it cannot be cultured or genetically manipulated. Here, we review recent progress in the application of modern molecular techniques to understanding the biological basis of this multistage disease and to the development of new tools for diagnosis, for predicting efficacy of treatment with alternative antibiotics, and for studying the transmission of infection through population networks.