title: Quantification of hepatitis B virus genomes and infectivity in human serum samples.
abstract: BACKGROUND
  Hepatitis B virus (HBV) infections are still a major health issue, with approximately 350 million people chronically infected with HBV worldwide. Information about the minimum copy number of HBV genomes required for infection would be useful as a reference for drug and vaccine development; for monitoring HBV patients during treatment; for screening of blood, organ, and tissue donors; and for regulating nucleic acid amplification assays for HBV.
  
  
  METHODS
  Serum samples from chronic carriers (hepatitis B surface antigen-positive and antibody to HBV core antigen-positive) of the three most common subtypes of HBV were studied; their infectivity titers had been evaluated previously in chimpanzees. The genotypes of the HBV samples were determined by DNA sequences and type-specific amino acids of the S gene of HBV. Copy numbers of HBV DNA were quantified by real-time TaqMan polymerase chain reaction (PCR) and by nested PCR applied to limiting dilutions. The copy number determined for each inoculum was compared with previously defined chimpanzee infectivity titers.
  
  
  RESULTS
  The genotypes of the HBV adw, ayw, and adr inocula were A, D, and C, respectively. The concentration of HBV DNA was determined to be 5.4 x 10(9), 2.5 x 10(9), and 3.1 x 10(8) genome equivalents (geq) per mL for serum samples containing the adw, ayw, and adr, respectively. The chimpanzee infectivity titers per milliliter of these initial HBV-containing serum samples were previously determined to be 10(7.5) for adw, 10(7.5) for ayw (MS-2 strain), and 10(8) for adr.
  
  
  CONCLUSIONS
  The minimal copy number of HBV DNA in chronic carriers of HBV that can infect the chimpanzee model was estimated to be from 3 to 169 geq based upon the three well-characterized inocula.
authors.affiliation: Division of Emerging and Transfusion Transmitted Diseases, CBER, FDA, Bethesda, Maryland, USA. chuchieh.hsia@fda.hhs.gov
authors.forename: Chu Chieh
authors.initials: CC
authors.lastname: Hsia
authors.forename: Robert H
authors.initials: RH
authors.lastname: Purcell
authors.forename: Mahmood
authors.initials: M
authors.lastname: Farshid
authors.forename: Peter A
authors.initials: PA
authors.lastname: Lachenbruch
authors.forename: Mei-Ying W
authors.initials: MY
authors.lastname: Yu
mesh_terms: D000818:Animals; D004279:DNA, Viral / Q000097:blood* / Q000235:genetics; D005814:Genes, Viral / Q000235:genetics; D005838:Genotype; D006509:Hepatitis B / Q000097:blood* / Q000235:genetics; D006514:Hepatitis B Surface Antigens / Q000097:blood; D006515:Hepatitis B virus / Q000235:genetics / Q000472:pathogenicity; D006801:Humans; D002679:Pan troglodytes; D016133:Polymerase Chain Reaction / Q000379:methods; D012680:Sensitivity and Specificity; D044967:Serum / Q000737:chemistry / Q000821:virology*; D013045:Species Specificity
chemical_list: D004279:DNA, Viral; D006514:Hepatitis B Surface Antigens