Objective To investigate the molecular basis of occult hepatitis B virus (HBV) infection (OBI) in Asian blood donors.
Design OBI donors from Hong Kong, Malaysia, Singapore, Taiwan and Thailand were tested for HBV serological markers, and strains were molecularly characterised.
Results Among 138 confirmed OBI carriers (median age 47 years), HBV genotypes B and C were dominant (60% and 34%, respectively) in agreement with the genotype distribution in chronically infected donors in the region. Viral load ranged between unquantifiable and 3670 IU/ml (median 11 IU/ml). Eleven per cent of OBIs showed an unusual anti-HBs-only serological profile without evidence of past vaccination for most of these individuals. Occult HBV strains showed a higher genetic diversity than strains from matched hepatitis B surface antigen (HBsAg)+ donors, irrespective of genotype. No unique genetic signature or evidence of reduced replication competence was found. Mutations in the vicinity of the pre-S2/S splice donor site were common in OBIB (44%) and OBIC (36%) strains. S regions from four OBI cases were transfected in HuH7 cells. Results showed limited HBsAg secretion and suggested that mutations disrupting the splice donor site structure may affect pre-S2/S mRNA splicing.
Conclusions There is indirect evidence that incomplete immune control is involved in the occurrence of OBI in Asian blood donors infected with genotypes B and C as observed in Europe with genotype A2 but to a lower extent than with genotype D. A post-transcriptional mechanism may play a role in HBsAg expression in some OBIs irrespective of HBV genotype.
- Hepatitis B virus
- occult HBV infection
- blood donors
- RNA splicing
- diagnostic virology
- hepatitis C
- hepatitis B
- molecular epidemiology
- chronic viral hepatitis
- hepatitis D
- hepatitis E
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Funding This study was supported by grants from the International Society of Blood Transfusion Foundation, the National Health Service Blood and Transplant, England, and Novartis.
Competing interests None.
Ethics approval Ethics approval was supplied by Hong Kong Red Cross Blood Centre Internal Review Board.
Provenance and peer review Not commissioned; externally peer reviewed.