| Syphilis is one of the common sexually transmitted diseases in the world. The World Health Organization recently estimated10.6million new cases of infectious syphilis each year. Treponema pallidum (T. pallidum), the pathogen of syphilis, can enter skin mucosa, cardiovascular system, nerve and bone. Syphilis infection can facilitate the transmission of HIV infection and the adverse development of AIDS. Syphilis can also increase the risk of adverse pregnancy outcomes, including abortion, stillbirth, premature delivery, low birth weight and congenital syphilis. China eliminated syphilis in1964, but syphilis resurged in late1970s after implementation of reform and opening policies because of rural-to-urban migration, higher-risk behaviors, and sexual networks of heterosexual, homosexual and bisexual contacts. According to surveillance results from the National Center for STD Control and Prevention, syphilis incidence has been increasing sharply since2003. In2011, syphilis incidence was as high as32.04per100,000persons, which was10.89%higher than that in2010. The annual number of new syphilis cases ranks third out of all categories B infectious diseases nationally, following tuberculosis and hepatitis B. It is very important to study the epidemiology, control and prevention of syphilis to decrease the transmission of syphilis in China.T. pallidum cannot be cultured in vitro, which makes syphilis research difficult. Since the1990s, it has been possible to investigate the molecular biology of syphilis due to the complete genome sequence determination of the Nichols strain. Molecular epidemiology is the integration of molecular biology with traditional epidemiologic research and a powerful tool for determining diversity and epidemiology of infectious diseases using molecular biomarkers. Molecular typing of T. pallidum clincal strains is an important aspect of the molecular epidemiology of syphilis. It helps to characterize syphilis transmission networks, trace infectious sources, differentiate between relapse and re-infection episodes, evaluate subtypes associated with clinical characteristics, and better understand the spatial, temporal and population distributions of T. pallidum. In1998, the first molecular typing method was introduced by the United States Centers for Disease Control and Prevention and is based on the interstrain variability of the acidic repeat protein gene and the T. pallidum repeat gene subfamily Ⅱ. Moreover, a recent study developed a third gene named tp0548with a better discriminatory typing power in2010at the University of Washington.Another important aspect of the molecular epidemiology of syphilis is monitoring macrolide antibiotic resistance, such as azithromycin. The use of azithromycin for the treatment of early syphilis offers certain advantages over conventional intramuscular therapy with benzathine penicillin G, including oral route of delivery with single-dose, no risk of anaphylactic shock, the ability to treat in the field and the convenience of partner-delivery therapy. The efficacy, safety and ease of azithromycin usage were verified by randomized controlled clinical trials. However, azithromycin treatment failures for early syphilis have been documented in multiple geographic locations in developed countries. Moreover, azithromycin resistance has been increasing each year and transmitting in certain sexual networks in these developed countries. Biological research has demonstrated that a single mutation from adenine to guanine in locus2058of the23SrRNA gene confers azithromycin resistance. Monitoring resistant strains helps to guide syphilis treatment in a defined time, space and population using the23SrRNA gene as a molecular biomarker.In China, four small-scale molecular typing studies, which were based on the arp and tprⅡ genes, have described the subtype distributions of T. pallidum in South Hunan, Guangzhou, Jiangmen and Shanghai. Shanghai has also reported the epidemiology of azithromycin resistant strains. China is a huge country with the severe resurgence of syphilis. The strain type distribution of T. pallidum and epidemiology of azithromycin resistance are still not well known due to the absence of molecular epidemiology data across multiple geographic areas.There are three sections for this study. Section one is a systematic review and meta-analysis of the molecular epidemiology of syphilis globally. A total of16published studies were included in five databases from Oct.17th1998to Dec.31st2010. The main results based on systematic analyses were as following:(1) primary lesions, such as genital ulcer, condyloma lata, papulae and mucosal patches, were better specimens for the molecular diagnosis and epidemiologic study of syphilis;(2) ear lobe scraping was a promising specimen type when no visible skin lesions existed, but it needs to be validated by more research with larger sample sizes;(3) there was substantial genetic diversity of T. pallidum globally and14d,14f,14a,13d and15d were the most prevalent subtypes in descending order;(4) subtype data associated with azithromycin resistance and neurosyphilis were limited.Section two discusses the establishment of laboratory methods for molecular diagnosis, genotyping and azithromycin-resistant mutant identification for syphilis. This section described a detailed methodology established for syphilis molecular epidemiology research in the STD reference laboratory of the National Center for STD Control and Prevention based on the systematic review of laboratory methods in the first section. Positive DNA was first screened by a diagnostic PCR assay of polA gene, which is unique to T. pallidum. Molecular typing was based on the interstrain variability of the arp, tpr subfamily Ⅱ and tp0548genes. Azithromycin resistance identification was based on a single mutation from adenine to guanine in locus2058of23SrRNA gene.Section three is a preliminary molecular epidemiology study of early syphilis in STD clinics in multiple geographic areas of China. We conducted a cross-sectional study in STD clinics from eight cities located in East, South and North China during the years2008to2011. A total of391outpatients with early syphilis were recruited based on an oral informed consent. Each subject was interviewed using a short structured questionnaire and encouraged to provide a moist skin lesion for specimen collection.211clinical specimens could be fully molecular typed and identified azithromycin-resistant mutations. Overall,27strain types were identified.14d/f accounted for39.8%prevalence and was the predominant strain type across China. Strain type distribution was significantly different across geographic areas (χ2=18.1,p=0.021).91.9%clinical strains were azithromycin resistant, and resistant mutations were significantly associated with history of macrolide antibiotics use (χ2=37.5,p<0.001). |
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