الفهرس 
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Abstract
Introduction : Occult HBV infection (OBI) is defined as the presence of HBV DNA in serum and/or liver tissue in the absence of hepatitis B surface antigen (HBsAg). The presence of anti-HBcAg antibodies without any other HBV serological marker is frequently found in different situations for example: presence of a vaccine escape mutant which is not detected by most of the currently available HBsAg detection tests. Aim of the work: Detection of possible genetic mutations within the surface region of HBV genome that may hinder expression and detection of serum HBs Ag. Patients and methods: This study was conducted on one group of patients that included 20 patients; they were selected according to their serological HBV markers ; having negative HBs Ag and positive total HBc Ab serological assay. The patients’ age ranged from 27 to 61 years, 15 of them were males and 5 were females. Samples were subjected to other HBV serological markers and conventional PCR test; in addition, sequencing and phylogentic analysis of HBV DNA positive samples were performed, and then amino acid sequences were aligned with standard hepatitis B sequence on Genebank database. Results: The study revealed that patients with positive HBV DNA showed higher incidence of associated HCV infection; they also showed obvious hypoalbuminemia and hyperbilirubinemia as a result of associated liver cirrhosis and HCC development. Phylogentic analysis of the sequenced samples demonstrated that the predominant HBV genotype was genotype D, especially subgenotype D1. Alignment results demonstrated amino acid substitutions in all sequenced samples. Conclusion : The prevalence of occult HBV in patients with HCV infection is remarkably high. In addition, there is a significant correlation between occult HBV and development of HCC. Alignment results demonstrated amino acid substitutions in all sequenced samples. These mutations could be involved in failure of HBs Ag detection, immunotherapy escape, or vaccine escape.