Chlamydia trachomatis serology as a means of monitoring intervention activities to eliminate trachoma as a public health problem

Trachoma causes blindness as a result of repeated ocular infection with Chlamydia trachomatis (Ct). International efforts are focused on eliminating trachoma as a public health problem by 2020; the World Health Organisation’s (WHO) and the Global Alliance for the Elimination of Trachoma by 2020 (GET2020) (1) recommend the SAFE strategy (Surgery to treat trichiasis, Antibiotics to treat infection with Ct, Facial cleanliness and Environmental change to reduce transmission) (2). Current implementation guidelines for the A, F and E aspects of the strategy are based on the prevalence of trachomatous inflammation-follicular (TF) in children aged 1-9 years. Antibiotics are administered as azithromycin mass drug administration (MDA) to all residents of districts wherein the prevalence of TF in 1-9 year old children is greater than 10% (3). As we approach the global elimination of trachoma, the prevalence of TF in children will decline towards the elimination threshold of 5%, and with it, the positive predictive value of TF. This may result in inappropriate, continued administration of antibiotics, which is a mis-use of valuable financial and person resources, as well as raising concerns about antimicrobial stewardship. Once the prevalence of TF in children aged 1-9 years is below 5%, re-emergence must be monitored. The WHO recommends a ‘pre-validation’ survey to determine if re-emergence has occurred (4). The 2014 Technical Consultation on Trachoma Surveillance (4) recommended exploring the district-level prevalence of TF, the district-level prevalence of conjunctival infection with Ct and the district-level prevalence of antibodies against Ct, to determine an appropriate measure, or combination of measures, for deciding when to stop MDA. Numerous methods exist for detecting antibodies against Ct antigens (5–9). Specimens may be collected by venepuncture or from fingerprick, stored as whole blood, serum or dried blood spots on filter paper, and assayed using enzyme-linked immunosorbent assays (ELISA), lateral flow assays (LFA), or multiplex bead assay (MBA); of theses, MBA allows for the testing for antibodies against numerous antigens from endemic infections, but the required instrumentation and reagents are more cost-intensive. Historically, serology for Ct fell out of favour due to the high cross-reaction with antigens from C pneumoniae, however, with the advent of new proteomic tools and assays with greater reported sensitivity and specificity, serology has re-emerged as a potential tool for monitoring the prevalence of antibody-inducing chlamydial infection (4,10,11). Both ELISA and MBA assays present output as numerical data, which must be translated to a population seroprevalence value. Therefore, a method must be determined for dichotomising numerical data and setting a threshold between seropositive and seronegative samples. Receiver 5 Operating Characteristic (ROC) curves have previously been used, but these rely on appropriate reference standards. Alternate methods that rely solely on the data generated within a study, such as finite mixture modelling, may be more appropriate (12–15). Once seropositivity has been estimated, it is of interest to detect changes in the age-specific seroprevalence of a population. Catalytic models have previously been used to monitor changes in the prevalence of malaria (13,16–22) and this methodology can be applied to detect changes in transmission as a proxy for the force of infection (FOI) as well as to estimate seroconversion rates, and to a lesser extent, seroreversion rates (13,19). The simplicity of dichotomous seroprevalence estimates may provide lower resolution information than the quantitative antibody levels. Recent work uses quantitative antibody levels to measure changes in transmission (23). Ensemble machine learning can be used to produce characteristic agespecific antibody curves that may reveal changes in population mean antibody levels that would otherwise be masked because changes occurred above or below the seropositivity threshold. There remain several areas to be elucidated. While antigens used in modern serological studies are considered specific for Ct, there is yet no way to distinguish between antibodies due to ocular infection or genital infection, making serological studies in anyone over the age of sexual debut a challenge. There is no standard reference for antibody levels, making a comparison between different studies challenging. The two most commonly used assays produce different output data: ELISAs measures optical density- the amount of light absorbed by the specimen- while MBAs detect fluorescence in an assayed specimen. An internal standard would allow for comparison between the two assays. This PhD research addresses several key questions about the use of serology and Ct-specific antibodies for monitoring the prevalence of trachoma. As more countries progress to eliminating trachoma as a public health problem by 2020, efforts will need to be increased to monitor and evaluate elimination efforts and to prevent re-emergence of the disease. Serological techniques may be ideal for such activities

Has Chlamydia trachomatis prevalence in young women in England, Scotland and Wales changed? Evidence from national probability surveys

We evaluate the utility of the National Surveys of Attitudes and Sexual Lifestyles (Natsal) undertaken in 2000 and 2010, before and after the introduction of the National Chlamydia Screening Programme, as an evidence source for estimating the change in prevalence of Chlamydia trachomatis (CT) in England, Scotland and Wales. Both the 2000 and 2010 surveys tested urine samples for CT by Nucleic Acid Amplification Tests (NAATs). We examined the sources of uncertainty in estimates of CT prevalence change, including sample size and adjustments for test sensitivity and specificity, survey non-response and informative non-response. In 2000, the unadjusted CT prevalence was 4.22% in women aged 18-24 years; in 2010, CT prevalence was 3.92%, a non-significant absolute difference of 0.30 percentage points (95% credible interval -2.8 to 2.0). In addition to uncertainty due to small sample size, estimates were sensitive to specificity, survey non-response or informative non-response, such that plausible changes in any one of these would be enough to either reverse or double any likely change in prevalence. Alternative ways of monitoring changes in CT incidence and prevalence over time are discussed

Advancing the public health applications of Chlamydia trachomatis serology

© 2018 Elsevier Ltd Genital Chlamydia trachomatis infection is the most commonly diagnosed sexually transmitted infection. Trachoma is caused by ocular infection with C trachomatis and is the leading infectious cause of blindness worldwide. New serological assays for C trachomatis could facilitate improved understanding of C trachomatis epidemiology and prevention. C trachomatis serology offers a means of investigating the incidence of chlamydia infection and might be developed as a biomarker of scarring sequelae, such as pelvic inflammatory disease. Therefore, serological assays have potential as epidemiological tools to quantify unmet need, inform service planning, evaluate interventions including screening and treatment, and to assess new vaccine candidates. However, questions about the performance characteristics and interpretation of C trachomatis serological assays remain, which must be addressed to advance development within this field. In this Personal View, we explore the available information about C trachomatis serology and propose several priority actions. These actions involve development of target product profiles to guide assay selection and assessment across multiple applications and populations, establishment of a serum bank to facilitate assay development and evaluation, and development of technical and statistical methods for assay evaluation and analysis of serological findings. The field of C trachomatis serology will benefit from collaboration across the public health community to align technological developments with their potential applications

Serological and PCR-based markers of ocular Chlamydia trachomatis transmission in northern Ghana after elimination of trachoma as a public health problem

Background Validation of elimination of trachoma as a public health problem is based on clinical indicators, using the WHO simplified grading system. Chlamydia trachomatis (Ct) infection and anti-Ct antibody responses (anti-Pgp3) have both been evaluated as alternative indicators in settings with varying levels of trachoma. There is a need to evaluate the feasibility of using tests for Ct infection and anti-Pgp3 antibodies at scale in a trachoma-endemic country and to establish the added value of the data generated for understanding transmission dynamics in the peri-elimination setting. Methodology/Principal findings Dried blood spots for serological testing and ocular swabs for Ct infection testing (taken from children aged 1–9 years) were integrated into the pre-validation trachoma surveys conducted in the Northern and Upper West regions of Ghana in 2015 and 2016. Ct infection was detected using the GeneXpert PCR platform and the presence of anti-Pgp3 antibodies was detected using both the ELISA assay and multiplex bead array (MBA). The overall mean cluster-summarised TF prevalence (the clinical indicator) was 0.8% (95% CI: 0.6–1.0) and Ct infection prevalence was 0.04% (95%CI: 0.00–0.12). Anti-Pgp3 seroprevalence using the ELISA was 5.5% (95% CI: 4.8–6.3) compared to 4.3% (95%CI: 3.7–4.9) using the MBA. There was strong evidence from both assays that seropositivity increased with age (p<0.001), although the seroconversion rate was estimated to be very low (between 1.2 to 1.3 yearly events per 100 children). Conclusions/Significance Infection and serological data provide useful information to aid in understanding Ct transmission dynamics. Elimination of trachoma as a public health problem does not equate to the absence of ocular Ct infection nor cessation in acquisition of anti-Ct antibodies

Serum biochemical parameters and cytokine profiles associated with natural African trypanosome infections in cattle.

BACKGROUND: Animal African trypanosomiasis (AAT) greatly affects livestock production in sub-Saharan Africa. In Ghana prevalence of AAT is estimated to range between 5 and 50%. Studies have reported serum biochemical aberrations and variability in cytokine profiles in animals during infection. However, information regarding the biochemical parameters and cytokine profiles associated with natural infections are limited. This study was therefore aimed at investigating changes in the levels of serum biochemical parameters and inflammatory cytokines during a natural infection. METHODS: Nested internal transcribed spacer (ITS)-based PCR and sequencing were used to characterise trypanosome infection in cattle at two areas in Ghana (Adidome and Accra) of different endemicities. The cattle were sampled at four to five-week intervals over a period of six months. Levels of serum biochemical parameters, including creatinine, cholesterol, alkaline phosphatase (ALP), alanine aminotransferase (ALT), total bilirubin and total protein and cytokines (interleukin 10, interleukin 4, interleukin 12, interferon gamma and tumor necrosis factor alpha) were measured in serum samples and then compared between infected cattle and uninfected controls. RESULTS: The predominant trypanosome species detected in Accra (non-endemic) and Adidome (endemic) were Trypanosoma theileri and Trypanosoma vivax, respectively. Serum biochemical parameters were similar between infected and uninfected cattle in Accra. Infected cattle at Adidome however, had significantly higher levels of ALP, creatinine, total protein and total bilirubin (P < 0.05) and significantly lower levels of cholesterol (P < 0.05) at specific time points. At basal levels and during infection, significantly higher pro-inflammatory to anti-inflammatory (Th1/Th2) cytokine ratios were observed in cattle at Adidome compared to Accra (P < 0.05), indicating a shift towards Th1 immune response in Adidome. Levels of IL-10 were, however, significantly elevated in infected cattle in Accra (P < 0.05), suggesting high anti-inflammatory cytokine response in Accra. CONCLUSION: These results suggests that cattle in an endemic area repeatedly infected with trypanosomes of different species or different antigenic types demonstrate high pro-inflammatory (Th1) immune response and biochemical alterations whereas cattle in a non-endemic area with predominantly chronic T. theileri infections demonstrate high anti-inflammatory response and no biochemical alterations