Transmissibility of Hepatitis B Virus (HBV) Infection through Blood Transfusion from Blood Donors with Occult HBV Infection

The prevalence and long term outcome of occult hepatitis B virus infections in community based populations

Features of occult hepatitis B infection in community-based populations have yet to be described. In this study we documented: (1) the prevalence and demographics, (2) associated serology and viral loads, and (3) clinical outcomes of occult hepatitis B infection in community-based populations. Hepatitis B surface antigen (HBsAg)-negative sera collected from three Northern Canadian communities (HBsAg prevalences: 11-12%) in 1983-1985 were tested for HBV-DNA by nested stage polymerase chain reaction. Of 706 HBsAg negative sera, 9 (1.3%) were HBV-DNA positive. The median age of occult hepatitis B infected patients at the time of sampling was 9.8 years (range 3.1-50.4 years) and six (67%) were female. Two (22%) individuals were anti-HBs positive (in the absence of prior vaccination). Viral loads were undetectable in all but two samples (2.40 and 2.86  log₁₀ IU/ml). Only one of the five (20%) patients who were assessed clinically, remained HBV-DNA positive at 25-30 year follow-up. There was no clinical, biochemical or radiologic evidence of chronic hepatitis, cirrhosis or hepatocellular carcinoma in these individuals or on review of the charts from the remaining four infected patients. The results of this study suggest that in community-based populations: (1) occult hepatitis B infection is not as common as HBsAg positive infection, (2) the majority of infected subjects are young females, (3) a minority are anti-HBs positive, (4) viral loads are either undetectable or low, and (5) in the absence of concurrent liver disease, occult hepatitis B infection does not appear to be associated with long term adverse clinical outcomes.

Mutations associated with occult hepatitis B virus infection result in decreased surface antigen expression in vitro

Occult hepatitis B virus (HBV) infection is characterized by the absence of detectable hepatitis B surface antigen (HBsAg) in the serum, despite detectable HBV DNA. Investigations of the mechanisms underlying the development of occult HBV infection are lacking in the current literature, although viral mutations in the surface region, resulting in decreased HBsAg expression or secretion, represent one potential mechanism. Wild-type HBsAg expression vectors were constructed from genotype-matched chronic HBV sequences. Site-directed mutagenesis was then utilized to introduce three genotype A mutations - M103I, K122R and G145A - associated with occult HBV infection in vivo, alone and in combination, into the wild-type HBsAg vectors. Transfection of Huh7 and HepG2 cell lines was performed, and cell culture supernatants and cell lysates were collected over 7 days to assess the effects of these mutations on extracellular and intracellular HBsAg levels. The G145A mutation resulted in significantly decreased extracellular and intracellular HBsAg expression in vitro. The most pronounced reduction in HBsAg expression was observed when all three mutations were present. The mutations evaluated in vitro in the current study resulted in decreased HBsAg expression and potentially increased hepatic retention and/or decreased hepatic secretion of synthesized HBsAg, which could explain the lack of HBsAg detection that is characteristic of occult HBV infection in vivo.

Occult Hepatitis B (OBH) in Clinical Settings

CONTEXT

Occult hepatitis B (OHB), or persistent HBV DNA in patients who are hepatitis B surface antigen (HBsAg) negative, is a recently recognized entity. In an attempt to summarize the issues, this review presents an overview of the current proposed hypothesis on the clinical relevance and also updates the knowledge on the classification of OHB in different clinical settings.

EVIDENCE ACQUISITION

OHB COULD BE FOUND IN DIFFERENT POPULATION AND CLINICAL BACKGROUNDS INCLUDING: viral co-infections (with either human immunodeficiency or hepatitis C viruses), HBV chronic carriers, dialysis patients, transplantation settings and certain clinical situations (named in here: special clinical settings) with no apparent distinguishable clinical parameters.

RESULTS

The exact magnitude, pathogenesis, and clinical relevance of OHB are unclear. Even the possible role exerted by this cryptic infection on liver disease outcome, and hepatocellular carcinoma development remains unknown.

CONCLUSIONS

Monitoring of Individuals with positive anti-HBc, mass immunization programs and improvement in diagnostic tools seem to be important to control the probability of transmission of HBV through cryptic HBV infection.

Two cases of transfusion-transmitted hepatitis B virus (HBV) infection in a low-endemic country before implementation of HBV nucleic acid testing

BACKGROUND

The risk of hepatitis B virus (HBV) transmission by transfusion is higher than that of other blood-borne viruses. In France, before the introduction of HBV nucleic acid testing (NAT) in 2010, blood donations were tested for hepatitis B surface antigen (HBsAg) and antibodies against hepatitis B core antigen, and the residual risk of HBV transfusion related to preseroconversion acute phase was estimated at 0.54 per million donations. The additional value of the implementation of a highly sensitive HBV NAT to prevent such transmissions is discussed.

STUDY DESIGN AND METHODS

Two lookback investigations based on HBV seroconversion of repeat donors were performed. Donors and recipients were followed up in multiple samples that were tested for HBV serologic and molecular markers.

RESULTS

The recipients have shown posttransfusion HBsAg seroconversion. The archived samples from the implicated donations were positive for HBV DNA at extremely low viral load in both cases. HBV isolates from donors and recipients of each case were organized in the same cluster with 100% identities into Genotypes A2 and B4, respectively. One recipient spontaneously recovered from infection while the second was successfully treated.

CONCLUSION

The present cases highlight the importance of introducing highly sensitive HBV NAT to prevent transmission. Moreover, the lookback studies based on appropriate molecular and serologic investigations of patients transfused with previous donations from newly identified HBV-infected repeat donors offer the opportunity to treat a recently infected recipient.

Hepatitis B virus in transfusion medicine: still a problem?

Hepatitis B virus (HBV) has probably evolved with humans for nearly 35,000 years. HBV diversified into 9 genotypes (A-I) presenting specific features directing epidemiology, clinical expression and testing. Genotypes E and C are more infectious and carry higher risk of chronicity and cancer. HBsAg blood screening implemented 40 years ago enormously decreased the risk of transfusion transmission but the remaining risk requires extremely sensitive nucleic acid testing (NAT) to be removed. Limitations of the host immune system, the impact of immunodeficiency and the mechanisms utilised for viral persistence were recently identified. HBV replication produces excess HBsAg and infectious and defective viral particles but screening assays for HBsAg or viral particles alone do not allow fully efficient detection, making necessary screening for both. The host immune system fails to completely control the virus that escapes and persists unrecognized at very low levels or as immuno-selected variants. Variants may not be identified by assays, explaining false negative results. Specific mutations may affect post-transcriptional mechanisms including HBV RNA splicing. Asymptomatic HBV infected blood donors are at risk of long-term complications through mechanisms to be understood for appropriate counselling. Infectivity of occult HBV infection (OBI) by transfusion appears low, anti-HBc (anti-core antigen) only being more infectious than anti-HBs (anti-S protein) positive units.

Challenges in hepatitis B detection among blood donors

PURPOSE OF REVIEW

The availability of hepatitis B virus (HBV) nucleic acid testing (NAT) for donor blood screening led to its implementation in low prevalence and high prevalence countries. Genomic detection was a substantial addition to HBV surface protein (HBsAg) screening by detecting window period infections and 'occult' HBV infections (OBIs), characterized by undetectable HBsAg, low viral load and presence of serological markers (anti-HBc and/or anti-HBs). OBIs are the result of multiple, poorly understood mechanisms including incomplete immune control mutations of the HBsAg antigenic determinants; abnormal expression of S gene; and inhibition of genome transcription. Infectivity for the recipient is high for window period blood and relatively low for OBIs.

RECENT FINDINGS

The number of cases identified by NAT ranges between 1 : 1000 and 1 : 50 000, depending on epidemiology and assay sensitivity whether NAT is implemented in individual donations or pools of samples. OBI donors are generally older than 45 years except in Africa, carry very low viral load (median 11-25  IU/ml) and have normal alanine transaminase levels. Cases carrying anti-HBc alone are more infectious than those with low level of anti-HBs. Evidence of HBsAg escape mutants that are undetected by commercial assays has been published. Inhibition of HBsAg mRNA production and export are potential mechanisms of OBI occurrence.

SUMMARY

HBV blood safety is improved by NAT for HBV DNA when applied to individual donations. Until the sensitivity of NAT is improved, both this method and HBsAg screening are needed to eliminate potentially infectious blood donations. Occult HBV characterization clarifies new facets of HBV natural history.

Hepatitis B virus transmission by blood transfusion during 4 years of individual-donation nucleic acid testing in South Africa: estimated and observed window period risk

BACKGROUND

Since October 2005, a total of 2,921,561 blood donations have been screened by the South African National Blood Service for hepatitis B virus (HBV) by individual-donation nucleic acid testing (ID-NAT). Over 4 years, 149 hepatitis B surface antigen-negative acute-phase HBV NAT-positive donations were identified (1:19,608). The lookback program identified one probable HBV transmission.

STUDY DESIGN AND METHODS

The complete genomes of HBV isolated from the donor and recipient were sequenced, cloned, and analyzed phylogenetically. The HBV window period (WP) transmission risk was estimated assuming a minimum infectious dose of 3.7 HBV virions and an incidence rate correction factor of 1.34 for transient detectability of HBV DNA.

RESULTS

Of 149 acute-phase HBV NAT yields, 114 (1:25,627) were classified as pre-antibody to hepatitis B core antigen (anti-HBc) WP and 35 (1:83,473) as post-anti-HBc WP. The acute-phase transmission risk in the HBV DNA-negative pre- and post-anti-HBc WPs (of 15.3 and 1.3 days, respectively) was estimated at 1:40,000 and 1:480,000, respectively. One HBV transmission (1:2,900,000) was identified in a patient who received a transfusion from an ID-NAT-nonreactive donor in the pre-anti-HBc WP. Sequence analysis confirmed transmission of HBV Subgenotype A1 with 99.7% nucleotide homology between donor and recipient strains. The viral burden in the infectious red blood cell unit was estimated at 32 (22-43) HBV DNA copies/20 mL of plasma.

CONCLUSION

We report the first known case of transfusion-transmitted HBV infection by blood screened using ID-NAT giving an observed HBV transmission rate of 0.34 per million. The estimated pre-acute-phase transmission risk in the ID-NAT screened donor population was 73-fold higher than the observed WP transmission rate.