Study On The Molecular Epidemiology Of Occult HBV Infection Among Healthy Young Chinese Adults

Objective: Occult HBV infection is defined as the persistence of HBV DNA inindividuals negative for HBV surface antigen (HBsAg), but positive for HBV DNA.The prevalence and mechanisms have not been elucidated because of the lowsensitivity of detection methods and the lack of mutual comparability. The purpose ofthis study are (1) To investigate the prevalence of occult Hepatitis B Virus (HBV)infection among healthy young people who had accepted hepatitis B vaccine in northof China,(2) To clone and sequence the whole HBV gene of occult HBV infection ofhealthy young people and to investigate the virological features and the mechanism ofoccult HBV infection.Methods:1176sera samples were collected from healthy young people who hadaccepted hepatitis B vaccine in north of China. Anti-HBcAb positive samples weretested by nested PCR using specific primers of the X and S region of the HBVgenome to investigate the prevalence of occult HBV infection.9entire linear HBVgenomes from HBsAg negative cases (OB1-OB9) were amplified using PCR method,and were cloned into pMD18T-HBV plasmid. Full length genomes were sequenced toanalyze the HBV gene variation.Results: In the research population, the HBV infection rate was2.6%（30/1176）,occult hepatitis B infection rate was0.76%(9/1176). Full-length HBV DNA from9patients with occult HBV infection was amplified and3-4strains of each patient weresuccessfully constructed, which was found belonging to genotype B and C. The genemutations in those cloned HBV genomes had been compared with82HBV surface antigen positive strains sequences from GENEBANK and showed as follows:(1)deletions in the pre-S1(OB1, OB3, OB5, and OB7) and preS2(OB3) regions,deletions in BCP (OB1) and C (OB3) regions were found in C genotype strains.(2)Deletions of C and P (OB5, OB7, OB2, and OB8) regions were found in all Bgenotype strains.(3) Point mutations and insert mutations were observed in most ofthe clones and it will lead a result of that functional and structural changes werehappened in expression of HBV protein.Conclusion: The prevalence of HBV infection and occult HBV infection remainexist among healthy young people who had accepted hepatitis B vaccine in north ofChina. Thus, more meticulous attention should be given to prevent HBV transmissionand occult HBV infection by blood transfusion or organ transplantation in endemicareas, the deletions in the pre-S, Basal core promoter (BCP）, core region(C）andpolymerase (P) regions that disable the regulatory elements may be responsible foroccult HBV infection. It was comfirmed that deletions in the preS1region and BCPdouble mutation play an important role in the process of liver cancer and it will be anew guidance in HCC diagnosis between occult HBV infector. Further studies onclinical implication and mechanism of occult HBV infection are required.