Characterization of occult hepatitis B virus strains in South African blood donors.
Since October 2005, all blood units collected in South Africa were screened individually for human immunodeficiency virus (HIV)-1, hepatitis B and C virus (HBV, HCV) genomes uncovering preseroconversion window period (WP) infections for each virus and occult HBV infections (OBIs) defined as persistent HBV DNA without detectable hepatitis B surface antigen (HBsAg). Samples identified as HBsAg-negative/DNA-positive were confirmed by combining real-time quantitative polymerase chain reaction, nested amplification, anti-HBc and anti-HBs. Amplified basic core promoter/precore, pre-S/S, and whole genome were sequenced, analyzed, and compared to 73 HBsAg+ strains. Genotype was determined by phylogenetic analysis. From 109 samples examined, 54 were classified as OBI, 14 as WP, 20 as false-positive, five as other classification, and 16 as undetermined due to lack of serological or follow-up data. OBI donors were predominantly males (67%), median age 31 years, black (54%), with normal alanine aminotransferase levels. Viral load ranged between unquantifiable and 518 IU/mL (median 5 IU/mL). Genotype A1 was more frequent (23 strains) than genotype D (seven strains). Genotype A1 strains were little mutated. In the major hydrophilic region, 56.5% strains were wild type or with few amino acid substitutions. Most important, all 13 full genome sequences presented 1 to 7 mutations known to or assumed to negatively impact viral replication. In particular, 6/13 sequences had a stop codon in the HBx gene translated into deletion of 117 or 19-25 C-terminus amino acids not found in 15 HBeAg+ HBsAg+ strains. One WP sequence with an HBx stop codon suggested infectivity.


CONCLUSIONS
Genotype A1 OBIs are different from genotype A2 and D OBIs in that there is little evidence of immune pressure as a major factor involved in OBI genesis. Limited replication appears mostly related to genetic viral defects.
Department of Haematology, University of Cambridge, Cambridge, UK. jpa1000@cam.ac.uk
Jean-Pierre
JP
Allain
Dalila
D
Belkhiri
Marion
M
Vermeulen
Robert
R
Crookes
Russell
R
Cable
Azin
A
Amiri
Ravi
R
Reddy
Arthur
A
Bird
Daniel
D
Candotti
D000328:Adult; D001769:Blood / Q000821:virology*; D001782:Blood Donors; D005260:Female; D006515:Hepatitis B virus / Q000235:genetics* / Q000302:isolation & purification*; D006801:Humans; D008297:Male; D008875:Middle Aged; D013019:South Africa; D055815:Young Adult