HCV genotype 6 is restricted in its distribution in South East Asia and it has been circulating for a long period of time. Phylogenetic and phylodynamic analysis on epidemic history of HCV focusing genotype 6 in South East Asia was explored, taking references from the pattern delineated in Liuzhou. Our results show that the date of most recent common ancestor (MRCA) of the whole HCV genotype 6 was estimated to be 100 years ago or more. There was an obvious increase of effective number of HCV genotype 6 infections in the part 20 years. Epidemic history of Subtype 6a and 6e/6d also showed the similar time course as that of the genotype 6. Interestingly, there was an increase of effective number of infections around 15-20 years ago which was maintained in the following decade for subtype 6a as well as 6e/6d. This specific pattern was consistent with the history of needle sharing in South East Asia, where the number of IDUs increased in the 1980s. The epidemic then spread to Southern China as evident by the increasing trend in Liuzhou. There was an exponential growth around 5 years ago involving subtype 6a predominantly, which might remain prevalent in Southern China in the coming decades. In conclusion, the study has shed new light on the transmission history of HCV, providing an explanation on the emergence of HCV genotype 6 in South East Asia. / HCV infection is an important public health problem associated with blood transfusion and needle-sharing in injection drug users (IDU) in Southern China. An understanding of the epidemiological pattern of the HCV infection, in conjunction with the transmission dynamics, would be beneficial for supporting effective prevention and control. This is accessed using a combination of molecular and public health approaches. / Through the Liuzhou Methadone Clinic, a total of 117 IDUs were recruited from Guangxi, Southern China. A majority of the IDUs (96%) were HCV antibody positive, of which 21% were HIV infected. Unlike HCV monoinfection, there was spatial heterogeneity in the distribution of HIV/HCV coinfection. The latter was also characterised by a higher prevalence of needle-sharing. Phylogenetic analysis of HCV revealed that genotype 6a was predominant in the study population. There were shorter genetic distances among the 6a samples compared to 3 other HCV genotypes/subtypes, 1a, 3a, and 3b. Our results suggested that HIV and HCV were both introduced at around the same time to the IDU populations in Southern China, followed by their differential spread as determined by the biologie characteristics of the virus and the intensity of behavioural risk. This pattern might be different from that in other South East Asian countries where HCV infections have probably predated HIV. / Tan, Yi. / Adviser: Kung Hsiang-fu. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3404. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 164-178). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.