Background Syphilis is resurgent in China, but there have been limited data on molecular epidemiology. A novel Treponema Pallidum (T pallidum) typing method that uses tp0548 gene in addition to arp and tpr E, G, J genes with greater discriminatory power has recently been developed. This study aimed to analyse T pallidum strain types across geographical areas in China using this novel method.
Methods From 2008 to 2010, genital specimens, including those from chancres, condyloma lata and mucosal patches, were collected from patients with clinically suspected primary or secondary syphilis in STI clinics in East China (Nanjing), South China (Guangzhou, Jiangmen and Fuzhou), Southwest China (Nanning and Chengdu), North China (Tianjin), and Northeast China (Harbin). All specimens were first amplified by PCR of polA gene to screen for positive DNA, followed by analysis of arp, tpr E,G, J and tp0548 genes for complete strain type. A χ2 test was used to compare the distribution of strain types across the 5 geographical areas.
Results Typeable T pallidum DNA was detected in 184 of 401 specimens, and 27 strain types were identified. Overall, 3 to 20 repeats (except 4, 11, and 19 repeats) and 25 repeats were found for the 60-bp arp gene. This was the first time 9 and 25 repeats for the arp gene have been detected. For the RFLP pattern of the tpr E, G, J genes, a, d, h, j and l were identified. For the sequence pattern of the tp0548 gene, c, e and f were identified. The distribution of strain types was significantly different across the geographical areas of China (χ2=29.2, p=0.008), but type 14d/f was most predominant within each geographical area (approximately 40% constituent ratio in each area). Taking all geographical areas into account, types 15d/f, 13d/f, 16d/f, and 14a/f were the next most common in descending order see Abstract P4-S3.04 figure 1.
Conclusions There is substantial genetic diversity of T pallidum in China. However, the overall predominance of a single 14d/f strain type may imply a potential link in sexual transmission of syphilis across geographical areas.
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