Development of a real-time PCR assay to detect Treponema pallidum in clinical specimens and assessment of the assay's performance by comparison with serological testing

Evaluation of a PCR test for detection of treponema pallidum in swabs and blood

Syphilis diagnosis is based on clinical observation, serological analysis, and dark-field microscopy (DFM) detection of Treponema pallidum subsp. pallidum, the etiological agent of syphilis, in skin ulcers. We performed a nested PCR (nPCR) assay specifically amplifying the tpp47 gene of T. pallidum from swab and blood specimens. We studied a cohort of 294 patients with suspected syphilis and 35 healthy volunteers. Eighty-seven of the 294 patients had primary syphilis, 103 had secondary syphilis, 40 had latent syphilis, and 64 were found not to have syphilis. The T. pallidum nPCR results for swab specimens were highly concordant with syphilis diagnosis, with a sensitivity of 82% and a specificity of 95%. Reasonable agreement was observed between the results obtained with the nPCR and DFM methods (kappa = 0.53). No agreement was found between the nPCR detection of T. pallidum in blood and the diagnosis of syphilis, with sensitivities of 29, 18, 14.7, and 24% and specificities of 96, 92, 93, and 97% for peripheral blood mononuclear cell (PBMC), plasma, serum, and whole-blood fractions, respectively. HIV status did not affect the frequency of T. pallidum detection in any of the specimens tested. Swab specimens from mucosal or skin lesions seemed to be more useful than blood for the efficient detection of the T. pallidum genome and, thus, for the diagnosis of syphilis.

Protocols for detection and typing of Treponema pallidum using PCR methods

Syphilis, caused by Treponema pallidum, is a sexually transmitted disease which was epidemic in Europe between the 15th and 20th century. From 2000 onwards it is worldwide mostly encountered among men who have sex with men but also among women in resource poor setting. Syphilis can easily be treated with penicillin but can become chronic, if left untreated. The disease develops in several stages with ulcerative lesions in the primary stage, and systemic spread to organs via the blood in later stages. Taking swab samples from these ulcerative lesions gives the best options for detection by PCR of T. palillidum. Alternatively blood samples can be analyzed in later stages. If tested positive in screening PCR assays, T. pallidum can also be typed by molecular methods, enabling molecular epidemiology. Different protocols are discussed in this chapter, that include all steps from sample collection, nucleic acid extraction, PCR, and detection. The combination of all steps together determine the final sensitivity and specificity of T. pallidum PCR.

Molecular detection of Treponema pallidum sp. pallidum in blood samples of VDRL-seroreactive women with lethal pregnancy outcomes: a retrospective observational study in northern Brazil

INTRODUCTION

Although control measures of maternal and congenital syphilis are available in Brazil, difficulties exist within the healthcare network in providing a laboratory diagnosis of the infection during the prenatal period. The objective of this study was to confirm the presence of Treponema pallidum by PCR in women with positive VDRL serology and lethal pregnancy outcomes, i.e., abortion, stillbirth and neonatal death.

METHODS

A retrospective study was conducted on VDRLseroreactive women with lethal pregnancy outcomes admitted to the Fundação Santa Casa de Misericórdia do Pará (FSCM-PA) between January and July 2004. Serum samples and DNA from whole blood were obtained at the time of screening by the VDRL test. These samples were analyzed by IgG ELISA, IgM FTA-Abs and simple PCR (polA).

RESULTS

During the study period, 0.7% (36/4,912) of women with lethal pregnancy outcomes presented a positive VDRL test. The polAgene was amplified in 72.7% (24/33) of these women, with 55.6% (20/36) and 94.4% (34/36) presenting IgM and IgG antibodies against T. pallidum, respectively. Comparison of these results showed a significant difference, with agreement between the PCR and IgM FTA-Abs results, suggesting that maternal syphilis was an active infection. No basic cause of death of the conceptus was reported in 97.2% (35/36) of cases. Among women who were submitted to the VDRL test during the prenatal period, only four of the nine seroreactive patients underwent treatment.

CONCLUSIONS

The high frequency of syphilis in the group studied indicates the fragility of the service of infection diagnosis, treatment and monitoring, compromising epidemiological control.

Getting the measure of syphilis: qPCR to better understand early infection

Objectives

Until recently, PCR had been used to detect but not quantify Treponema pallidum. To understand infection kinetics of this uncultivable organism, a real-time PCR assay was developed to quantify 47 kDa membrane lipoprotein gene DNA (tpp47).

Methods

Assay specificity was determined against DNA from humans, skin organisms and sexually transmitted pathogens. tpp47 DNA (Nichols strain) was used to construct a standard curve for T pallidum quantification. Blood and ulcer samples were obtained from 99 patients being investigated or screened for syphilis and tpp47 was quantified.

Results

The assay was specific, not cross-reactive with other organisms tested and sensitive, with a detection limit of a single copy of tpp47 DNA. For ulcer samples, the assay was 100% sensitive and 97.14% specific. Sensitivity fell to 34.1% for blood samples but specificity remained high (100%). tpp47 DNA was more commonly detected, and at a higher copy number, in blood of patients with secondary infection (sensitivity 57.89%) compared with primary infection. Quantity of tpp47 DNA was higher in primary infection ulcers, especially in HIV-1-positive patients, than in ulcers persisting into secondary disease.

Conclusions

Quantifying T pallidum provides insight into syphilis infection kinetics: Ulcers of primary disease in HIV-1-positive patients are perhaps more infectious and the presence and load of T pallidum bacteraemia is variable, with a peak in the secondary stage. Quantitative PCR has the potential to map T pallidum infection and to highlight the impact of HIV on syphilis.

Treponema infection associated with genital ulceration in wild baboons

The authors describe genital alterations and detailed histologic findings in baboons naturally infected with Treponema pallidum. The disease causes moderate to severe genital ulcerations in a population of olive baboons (Papio hamadryas anubis) at Lake Manyara National Park in Tanzania. In a field survey in 2007, 63 individuals of all age classes, both sexes, and different grades of infection were chemically immobilized and sampled. Histology and molecular biological tests were used to detect and identify the organism responsible: a strain similar to T pallidum ssp pertenue, the cause of yaws in humans. Although treponemal infections are not a new phenomenon in nonhuman primates, the infection described here appears to be strictly associated with the anogenital region and results in tissue alterations matching those found in human syphilis infections (caused by T pallidum ssp pallidum), despite the causative pathogen's greater genetic similarity to human yaws-causing strains.

Symptomatic and asymptomatic early neurosyphilis in HIV-infected men who have sex with men: a retrospective case series from 2000 to 2007

Background The rise in serious complications of early syphilis, including neurosyphilis, particularly in those with HIV infection and in men who have sex with men (MSM), is of concern. Objectives: To review the manifestations and management of neurosyphilis in a population of HIV-infected MSM. Methods: Retrospective review of patients with HIV and early neurosyphilis in three centres in Melbourne, Australia, in 2000–07. Results: Eighteen male HIV patients met the criteria for diagnosis of early neurosyphilis. Thirteen patients (72.2%) had neurological symptoms: six with headache (33.3%), four with tinnitus (22.2%) and five with impaired vision (27.8%), and one patient each with ataxia, leg weakness and anal discharge with faecal incontinence. Five patients (27.8%) reported no neurological symptoms. All had serum rapid plasma reagin (RPR) titres ≥1 : 32 and all except one had cerebrospinal fluid positive for syphilis fluorescent treponemal antibodies-absorbed. After treatment with 14–15 days of 1.8 g intravenous benzylpenicillin 4-hourly, 12 of 17 patients (71%) demonstrated a four-fold drop in serum RPR titre over 6–12 months and were considered successfully treated. A rise in RPR was noted in three patients during the 12-month follow-up period, suggesting re-infection or recurrence. Conclusion: HIV-infected patients found to have syphilis either because of symptoms or by routine screening should be carefully assessed for neurological, ophthalmic and otological symptoms and signs. A low threshold for a diagnostic lumbar puncture to exclude the diagnosis of neurosyphilis enables appropriate administration and dose of penicillin for treatment, which appears successful in ~75% of cases.

The intersection between HIV and syphilis in men who have sex with men: some fresh perspectives

Syphilis is increasing in men who have sex with men and disproportionately affects HIV-infected men. Here we review the epidemiology, diagnostic techniques, treatment guidelines, follow-up procedures and control of syphilis. The difference in these factors in HIV-infected men and uninfected men and evidence for this is reviewed. We explain that HIV-infected men are at higher risk of syphilis acquisition as a result of different behavioral factors. Thus, some control strategies may be different for HIV-infected men owing to these factors and also because HIV-infected men are more closely linked with medical care. There is no strong evidence to suggest there should be any differences in diagnostic techniques, treatment guidelines or follow-up procedures between HIV-infected and uninfected men.

Frequent screening for syphilis as part of HIV monitoring increases the detection of early asymptomatic syphilis among HIV-positive homosexual men

BACKGROUND

Syphilis continues to be a significant public health problem among HIV-positive men who have sex with men (MSM) internationally. This study aimed to determine whether the routine inclusion of syphilis serology with every blood test performed as part of HIV monitoring increases the detection of early asymptomatic syphilis among HIV-positive MSM.

METHODS

We examined the effect of this intervention, implemented in January 2007, on the detection of early asymptomatic syphilis among HIV-positive MSM attending the Melbourne Sexual Health Centre, Australia, and compared this with the previous clinic policy of annual syphilis screening.

RESULTS

In the 18 months before and after the intervention, the median number of syphilis tests performed per man per year was 1 and 2, respectively. The proportion of MSM diagnosed with early syphilis who were asymptomatic was 21% (3 of 14) and 85% (41 of 48) for the 2 respective periods (P = 0.006). The time between the midpoint since last syphilis serology and diagnosis of syphilis was a median of 107 days (range 9-362) and 45 days (range 23-325) for the 2 periods, respectively (P = 0.018).

CONCLUSIONS

The inclusion of routine syphilis serology with every blood test performed as part of HIV monitoring in HIV-positive MSM resulted in a large increase in the proportion of men diagnosed with early asymptomatic syphilis. This simple intervention probably also decreased the duration of infectiousness, enhancing syphilis control while also reducing morbidity.

Clinical value of Treponema pallidum real-time PCR for diagnosis of syphilis

The diagnosis of syphilis can be complicated when it is based on diverse clinical manifestations, dark-field microscopy, and serology. In the present study, therefore, we examined the additional clinical value of a Treponema pallidum real-time TaqMan PCR for the detection of primary and secondary syphilis. The additional value of the T. pallidum real-time PCR for the diagnosis of primary syphilis was evaluated by the use of three different algorithms: (i) a head-to-head comparison of the dark-field microscopy result and the T. pallidum real-time PCR result, (ii) comparison of the clinical diagnosis made in a sexually transmitted infection clinic (STI) (including by dark-field microscopy) and the T. pallidum real-time PCR result, and (iii) comparison of the clinical diagnosis made in a general practitioner's office (without dark-field microscopy) and the T. pallidum real-time PCR result. A fourth algorithm was used to determine the performance of the T. pallidum real-time PCR regarding the detection of secondary syphilis. From December 2006 to April 2008, 716 patients with suspected cases of primary syphilis and 133 patients with suspected cases of secondary syphilis were included in the study. A kappa value of 0.601 was found for the agreement between dark-field microscopy and the T. pallidum real-time PCR. Good agreement was found between the T. pallidum real-time PCR and both the diagnosis of the general practitioner (kappa = 0.745) and the diagnosis of the STI clinic (kappa = 0.769). The sensitivity with respect to the STI clinic diagnosis was 72.8%, the specificity was 95.5%, the positive predictive value was 89.2%, and the negative predictive value was 95.0%. The T. pallidum real-time PCR is a fast, efficient, and reliable test for the diagnosis of primary syphilis in an STI outpatient clinic and a general practitioner setting, but it has no added diagnostic value for the diagnosis of secondary syphilis.

Molecular characterization of syphilis in patients in Canada: azithromycin resistance and detection of Treponema pallidum DNA in whole-blood samples versus ulcerative swabs

Although detection of Treponema pallidum DNA in whole-blood specimens of syphilis patients has been reported, it is uncertain at what stage of the disease such specimens are most suitable for the molecular diagnosis of syphilis. Also, few studies have directly compared the different gene targets for routine laboratory diagnostic usage in PCR assays. We examined 87 specimens from 68 patients attending two urban sexually transmitted disease clinics in Alberta, Canada. PCR was used to amplify the T. pallidum tpp47, bmp, and polA genes as well as a specific region of the 23S rRNA gene linked to macrolide antibiotic susceptibility. In primary syphilis cases, PCR was positive exclusively (75% sensitivity rate) in ulcerative swabs but not in blood specimens, while in secondary syphilis cases, 50% of the blood specimens were positive by PCR. Four out of 14 (28.6%) of our PCR-positive syphilis cases were found to be caused by an azithromycin-resistant strain(s). Our results confirmed that swabs from primary ulcers are the specimens of choice for laboratory diagnostic purposes. However, further research is required to determine what specimen(s) would be most appropriate for molecular investigation of syphilis in secondary and latent syphilis.

[Utility of molecular biology techniques in the diagnosis of sexually transmitted diseases and genital infections]

Historically, the diagnosis of sexually transmitted diseases (STDs) has been difficult. The introduction of molecular biology techniques in microbiological diagnosis and their application to non-invasive samples has produced significant advances in the diagnosis of these diseases. Overall, detection of Neisseria gonorrhoeae by molecular biology techniques provides a presumptive diagnosis and requires confirmation by culture in areas with a low prevalence. For Chlamydia trachomatis infections, these techniques are considered to be the most sensitive and specific procedures for mass screening studies, as well as for the diagnosis of symptomatic patients. Diagnosis of Mycoplasma genitalium infection by culture is very slow and consequently molecular techniques are the only procedures that can provide relevant diagnostic information. For Treponema pallidum, molecular techniques can provide direct benefits in the diagnosis of infection. Molecular techniques are not established for the routine diagnosis of donovanosis, but can be recommended when performed by experts. Molecular methods are advisable in Haemophilus ducreyi, because of the difficulties of culture and its low sensitivity. In genital herpes, molecular techniques have begun to be recommended for routine diagnosis and could soon become the technique of choice. For other genital infections, bacterial vaginosis, vulvovaginal candidosis and trichomoniasis, diagnosis by molecular methods is poorly established. With genital warts, techniques available for screening and genotyping of endocervical samples could be used for certain populations, but are not validated for this purpose.

Syphilis and HIV co-infection

Syphilis is a complex disease, which is sexually transmitted. The incidence of syphilis is rising all over the world, partly due to the increased transmission in HIV patients and other high risk groups such as men who have sex with men. Interestingly syphilis itself facilitates HIV infection in several ways. Great importance exists in recognition of both diseases and their complex interactions. This article will review the manifestations of syphilis in the context of HIV infected patients, and the challenging diagnosis and management of these patients.

Comparison of conventional, nested, and real-time PCR assays for rapid and accurate detection of Vibrio vulnificus

We conducted a prospective study to target toxR in the blood of patients with skin and soft tissue infections who were admitted to four tertiary hospitals to assess the clinical usefulness of real-time quantitative PCR (Q-PCR) as a diagnostic technique. We performed conventional PCR (C-PCR), nested PCR (N-PCR), and Q-PCR assays and compared the results to those obtained using the "gold standard" of microbiological culture. The lower detection limit for the Q-PCR assay was 5 x 10(0) copies/microl. By use of blood samples of patients with skin and soft tissue infections, the sensitivities of the C-PCR and N-PCR assays against the target toxR gene of V. vulnificus as diagnostic tools were determined to be 45% and 86%, respectively. The C-PCR and N-PCR assays had specificities of 100% and 73%, respectively. When we adopted a crossing-point (cp) cutoff value of <38 cp as a positive result, the Q-PCR assay had 100% sensitivity and specificity. Q-PCR to detect V. vulnificus-specific genes is not only the most sensitive and specific of the techniques but also the most rapid diagnostic method. Therefore, the appropriate application of the Q-PCR assay using blood is useful for the rapid diagnosis and subsequent treatment of V. vulnificus sepsis.

Syphilis in the United States: an update for clinicians with an emphasis on HIV coinfection

Diagnosis and treatment of syphilis are challenging because of its variable clinical presentation and course and the lack of definitive tests of cure after treatment. This review of the most recent literature on the epidemiology, clinical manifestations, current diagnosis, and treatment of syphilis is focused toward clinicians who treat patients with this disease. Syphilis coinfection with human immunodeficiency virus is emphasized because it is increasingly common in the United States and affects the initial presentation, disease course, diagnosis, and treatment of syphilis. Of particular consequence is the effect of human immunodeficiency virus on the clinical diagnosis, prevalence, and course of neurosyphilis, one of the most serious consequences of syphilis infection.

Detection of azithromycin resistance in Treponema pallidum by real-time PCR

We describe a real-time PCR assay for the discrimination of azithromycin-resistant and -susceptible strains of Treponema pallidum. This assay is rapid and allows for as many as 30 clinical specimens to be analyzed simultaneously without the need for DNA sequencing.

Assessment of the kinetics of Treponema pallidum dissemination into blood and tissues in experimental syphilis by real-time quantitative PCR

Little is known about the size and kinetics of treponemal burdens in blood and tissues during acquired or experimental syphilitic infection. We used real-time quantitative PCR to measure Treponema pallidum DNA levels in rabbits infected intratesticularly with the prototype Nichols strain. At the outset, we performed a series of in vitro blood spiking experiments to determine the effect of blood processing procedures on the distribution of treponemes in various blood components. T. pallidum DNA levels in plasma and whole blood were approximately 10-fold higher than those in serum and more than 200-fold greater than those in peripheral blood mononuclear cells (PBMCs). Ten rabbits were inoculated intratesticularly with doses of treponemes ranging from 4 x 10(7) to 2 x 10(8) organisms. In five rabbits, T. pallidum DNA levels were measured sequentially in serum, plasma, whole blood, and PBMCs until sacrifice at peak orchitis, at which time brain, kidney, liver, spleen, and testicles were harvested; blood and organs were also harvested at orchitis from the other five rabbits. T. pallidum DNA was detected in plasma within 24 h postinfection. Treponeme levels in whole blood and blood components increased significantly with the development of peak orchitis. Overall, levels in serum and PBMCs were lower than those in plasma and whole blood; this disparity was particularly marked at early time points. Significantly greater numbers of spirochetes were found in the spleen than in liver, kidney, or brain tissue at the time of sacrifice. Our findings highlight the remarkable capacity of T. pallidum to disseminate from the site of infection to blood and tissues, and they identify the spleen as a prime target for treponemal invasion.