Variable In Vivo Hepatitis D Virus (HDV) RNA Editing Rates According to the HDV Genotype

Human hepatitis delta virus (HDV) is a small defective RNA satellite virus that requires hepatitis B virus (HBV) envelope proteins to form its own virions. The HDV genome possesses a single coding open reading frame (ORF), located on a replicative intermediate, the antigenome, encoding the small (s) and the large (L) isoforms of the delta antigen (s-HDAg and L-HDAg). The latter is produced following an editing process, changing the amber/stop codon on the s-HDAg-ORF into a tryptophan codon, allowing L-HDAg synthesis by the addition of 19 (or 20) C-terminal amino acids. The two delta proteins play different roles in the viral cell cycle: s-HDAg activates genome replication, while L-HDAg blocks replication and favors virion morphogenesis and propagation. L-HDAg has also been involved in HDV pathogenicity. Understanding the kinetics of viral editing rates in vivo is key to unravel the biology of the virus and understand its spread and natural history. We developed and validated a new assay based on next-generation sequencing and aimed at quantifying HDV RNA editing in plasma. We analyzed plasma samples from 219 patients infected with different HDV genotypes and showed that HDV editing capacity strongly depends on the genotype of the strain.

Detection and Genetic Characterization of Hepatitis B and D Viruses: A Multi-Site Cross-Sectional Study of People Who Use Illicit Drugs in the Amazon Region

Hepatitis B (HBV) and delta (HDV) viruses are endemic in the Amazon region, but vaccine coverage against HBV is still limited. People who use illicit drugs (PWUDs) represent a high-risk group due to common risk behavior and socioeconomic factors that facilitate the acquisition and transmission of pathogens. The present study assessed the presence of HBV and HBV-HDV co-infection, identified viral sub-genotypes, and verified the occurrence of mutations in coding regions for HBsAg and part of the polymerase in HBV-infected PWUDs in municipalities of the Brazilian states of Amapá and Pará, in the Amazon region. In total, 1074 PWUDs provided blood samples and personal data in 30 municipalities of the Brazilian Amazon. HBV and HDV were detected by enzyme-linked immunosorbent assay and polymerase chain reaction. Viral genotypes were identified by nucleotide sequencing followed by phylogenetic analysis, whereas viral mutations were analyzed by specialized software. High rates of serological (32.2%) and molecular (7.2%) markers for HBV were detected, including cases of occult HBV infection (2.5%). Sub-genotypes A1, A2, D4, and F2a were most frequently found. Escape mutations due to vaccine and antiviral resistance were identified. Among PWUDs with HBV DNA, serological (19.5%) and molecular (11.7%) HDV markers were detected, such as HDV genotypes 1 and 3. These are worrying findings, presenting clear implications for urgent prevention and treatment needs for the carriers of these viruses.

Demographics and outcomes of hepatitis B and D: A 10-year retrospective analysis in a Swiss tertiary referral center

BACKGROUND

Hepatitis B virus (HBV) is a major global health challenge with approximately 250-350 million chronically infected individuals. An improved understanding of the demographic features and outcomes of chronic HBV infection and hepatitis D virus (HDV) infection in low-endemic areas may improve prevention, early identification and management both at individual and community levels. Here, we retrospectively analyzed the demographic and clinical characteristics, treatment rates and outcomes of adult patients with chronic HBV infection with or without HDV coinfection examined at Lausanne University Hospital, Switzerland over a 10-year period.

METHODS

We analyzed the medical records of all adult patients with chronic HBV and HDV infection examined in our center between 2007 and 2016. Liver-related outcome was defined as the occurrence of cirrhosis, hepatocellular carcinoma, liver transplantation or liver-related death. Analyses were performed using logistic regression and results were reported as odds ratio (OR) and 95% confidence interval (CI).

RESULTS

Of 672 consecutive patients, 421 (62.6%) were male, median age was 36 years (interquartile range, 28-46 years), and 233 (34.7%) were of African origin. The prevalence of HDV coinfection was 7.1% and the proportion of anti-HDV-positive patients with detectable HDV RNA was 70.0%. In multivariate analysis, HDV coinfection was the strongest predictor for liver-related outcome (OR 6.06, 95% CI 2.93-12.54, p<0.001), followed by HBeAg positivity (OR 2.47, 95% CI 1.30-4.69, p = 0.006), age (OR per 10-year increase 2.03, 95% CI 1.63-2.52, p<0.001) and sex (OR for female 0.39, 95% CI 0.22-0.71, p = 0.002). The predictive accuracy of the multivariate model was high (receiver operator characteristic area under the curve 0.81).

CONCLUSION

This retrospective study underscores the importance of migration in the epidemiology of chronic hepatitis B in low-endemic areas. HDV coinfection, HBeAg positivity and age predicted liver-related outcomes while female sex had a protective effect.

Diversification of mammalian deltaviruses by host shifting

Hepatitis delta virus (HDV) is an unusual RNA agent that replicates using host machinery but exploits hepatitis B virus (HBV) to mobilize its spread within and between hosts. In doing so, HDV enhances the virulence of HBV. How this seemingly improbable hyperparasitic lifestyle emerged is unknown, but it underpins the likelihood that HDV and related deltaviruses may alter other host-virus interactions. Here, we show that deltaviruses diversify by transmitting between mammalian species. Among 96,695 RNA sequence datasets, deltaviruses infected bats, rodents, and an artiodactyl from the Americas but were absent from geographically overrepresented Old World representatives of each mammalian order, suggesting a relatively recent diversification within the Americas. Consistent with diversification by host shifting, both bat and rodent-infecting deltaviruses were paraphyletic, and coevolutionary modeling rejected cospeciation with mammalian hosts. In addition, a 2-y field study showed common vampire bats in Peru were infected by two divergent deltaviruses, indicating multiple introductions to a single host species. One vampire bat-associated deltavirus was detected in the saliva of up to 35% of individuals, formed phylogeographically compartmentalized clades, and infected a sympatric bat, illustrating horizontal transmission within and between species on ecological timescales. Consistent absence of HBV-like viruses in two deltavirus-infected bat species indicated acquisitions of novel viral associations during the divergence of bat and human-infecting deltaviruses. Our analyses support an American zoonotic origin of HDV and reveal prospects for future cross-species emergence of deltaviruses. Given their peculiar life history, deltavirus host shifts will have different constraints and disease outcomes compared to ordinary animal pathogens.

Animal models for the study of human hepatitis B and D virus infection: New insights and progress

Hepatitis B virus (HBV) is a member of the Hepadnaviridae family and infects hepatocytes, leading to liver pathology in acutely and chronically infected individuals. Co-infection with Hepatitis D virus (HDV), which requires the surface proteins of HBV to replicate, can exacerbate this disease progression. Thus, the >250 million people living with chronic HBV infection, including 13 million co-infected with HDV, would significantly benefit from an effective and affordable curative treatment. Animal models are crucial to the development of innovative disease therapies, a paradigm repeated again and again throughout the fields of immunology, neurology, reproduction, and development. Unfortunately, HBV has a highly-restricted species tropism, infecting limited species including humans, chimpanzees, and treeshrews. The first experimentally controlled studies of HBV infection were following inoculation of human volunteers in 1942, which identified the transmissibility of hepatitis through serum transfer and led to the hypothesis that the etiological agent was viral. Subsequent research in chimpanzees (Desmyter et al., 1971; Lichter, 1969) and later in other species, such as the treeshrews (Walter et al., 1996; Yan et al., 1996), further confirmed the viral origin of hepatitis B. Shortly thereafter, HBV-like viral infections were identified in woodchucks (Summers et al., 1978; Werner et al., 1979) and ducks, and much of our understanding of HBV replication can be attributed to these important models. However, with the exodus of chimpanzees from research and the limited reagents and historical data for treeshrews and other understudied species, there remains an urgent need to identify physiologically relevant models of chronic HBV infection. While large strides have been made in generating such models, particularly over the past two decades, there is still no available model that faithfully recapitulates the immunity and pathogenesis of HBV infection. Here, we discuss recent advancements in the generation of murine and non-human primate (NHP) models of HBV/HDV infection.

Chronic hepatitis delta: A state-of-the-art review and new therapies

Chronic delta hepatitis is the most severe form of viral hepatitis affecting nearly 65 million people worldwide. Individuals with this devastating illness are at higher risk for developing cirrhosis and hepatocellular carcinoma. Delta virus is a defective RNA virus that requires hepatitis B surface antigen for propagation in humans. Infection can occur in the form of a co-infection with hepatitis B, which can be self-limiting, vs superinfection in a patient with established hepatitis B infection, which often leads to chronicity in majority of cases. Current noninvasive tools to assess for advanced liver disease have limited utility in delta hepatitis. Guidelines recommend treatment with pegylated interferon, but this is limited to patients with compensated disease and is efficacious in about 30% of those treated. Due to limited treatment options, novel agents are being investigated and include entry, assembly and export inhibitors of viral particles in addition to stimulators of the host immune response. Future clinical trials should take into consideration the interaction of hepatitis B and hepatitis D as suppression of one virus can lead to the activation of the other. Also, surrogate markers of treatment efficacy have been proposed.

Insight into the Contribution and Disruption of Host Processes during HDV Replication

Hepatitis delta virus (HDV) is unique among animal viruses. HDV is a satellite virus of the hepatitis B virus (HBV), however it shares no sequence similarity with its helper virus and replicates independently in infected cells. HDV is the smallest human pathogenic RNA virus and shares numerous characteristics with viroids. Like viroids, HDV has a circular RNA genome which adopts a rod-like secondary structure, possesses ribozyme domains, replicates in the nucleus of infected cells by redirecting host DNA-dependent RNA polymerases (RNAP), and relies heavily on host proteins for its replication due to its small size and limited protein coding capacity. These similarities suggest an evolutionary relationship between HDV and viroids, and information on HDV could allow a better understanding of viroids and might globally help understanding the pathogenesis and molecular biology of these subviral RNAs. In this review, we discuss the host involvement in HDV replication and its implication for HDV pathogenesis.

The functional role of sodium taurocholate cotransporting polypeptide NTCP in the life cycle of hepatitis B, C and D viruses

Chronic hepatitis B, C and D virus (HBV, HCV and HDV) infections are a major cause of liver disease and cancer worldwide. Despite employing distinct replication strategies, the three viruses are exclusively hepatotropic, and therefore depend on hepatocyte-specific host factors. The sodium taurocholate co-transporting polypeptide (NTCP), a transmembrane protein highly expressed in human hepatocytes that mediates the transport of bile acids, plays a key role in HBV and HDV entry into hepatocytes. Recently, NTCP has been shown to modulate HCV infection of hepatocytes by regulating innate antiviral immune responses in the liver. Here, we review the current knowledge of the functional role and the molecular and cellular biology of NTCP in the life cycle of the three major hepatotropic viruses, highlight the impact of NTCP as an antiviral target and discuss future avenues of research.

Prevalence and predictors for compensated Advanced Chronic Liver Disease (c-ACLD) in patients with chronic Hepatitis Delta Virus (HDV) infection

Objective

The study aimed to evaluate the prevalence and predictor factors for compensated advanced chronic liver disease (c-ACLD) in patients with hepatitis Delta virus (HDV) infection.

Methods

This cross-sectional study included consecutive HDV-infected patients defined by positive anti-HDV. Patients with hepatitis C coinfection, liver transplantation or presence of conditions that limit liver (LSM) or spleen stiffness measurement (SSM) were excluded. Blood tests, abdominal ultrasound, SSM and LSM by transient elastography (FibroScan^®) were performed at the same day. Alcohol consumption was quantified using the AUDIT score and c-ACLD was defined by LSM ≥ 15 kPa performed by an experimented operator blinded for clinical and laboratory data.

Results

101 patients were eligible and few patients were excluded due to negative anti-HDV (n = 7), hepatitis C coinfection (n = 2), liver transplantation (n = 10) and limitation for LSM or SSM (n = 5). Therefore, 77 patients [61% male, age = 43 (IQR,36–52) years] were included. The prevalence of c-ACLD was 57% (n = 44/77). Patients with c-ACLD had a higher rate of detectable HBV viral load (p = 0.039), higher levels of transaminases, GGT, alkaline phosphatases, total bilirubin and INR (p<0.001 for all), as well as lower platelet count and albumin levels (p>0.001 for both) compared to those without c-ACLD. Patients with c-ACLD had higher SSM [65.2 (IQR,33.8–75.0) vs 21.8 (16.5–32.0) kPa; p<0.001] and higher splenic volume [475 (IQR,311–746) vs 154 (112–283) cm³; p<0.001] compared to those without. Detectable HBV viral load (>10 UI/ml), alkaline phosphatase (per IU/L) and GGT levels (per IU/L) were independently associated with c-ACLD in all multivariate models. Splenic volume [per cm³,OR = 1.01 (95%CI,1.01–1.02);p = 0.002], SSM [per kPa, OR = 1.04 (1.01–1.07);p = 0.012] and splenomegaly [yes vs no,OR = 28.45 (4.42–182.95);p<0.001] were independently associated with c-ACLD.

Conclusions

The prevalence of c-ACLD was high in patients with chronic HDV infection in western Amazon basin. HBV viral load, liver enzymes and splenic features can be used to predict severe liver disease in HDV-infected patients.

[The algorithms of etiologic laboratory diagnostic of parenteral viral hepatitis]

The article considers methods of laboratory diagnostic of parenteral viral hepatitis. The approaches ensuring single-valued differentiation of infected patients are determined. The various methods of evaluation of activity of infection process are presented. The algorithm of complex laboratory analysis concerning presence of parenteral viral hepatitis (B, C, D, G, TT, SEN) was proposed to ensure maximal informative minimum of laboratory analyses permitting fast and single-valued interpretation of received diagnostic data.

Entry of hepatitis B and hepatitis D virus into hepatocytes: Basic insights and clinical implications

For almost three decades following the discovery of the human Hepatitis B Virus (HBV) the early events of virus infection (attachment to hepatocytes, specific binding to a receptor on hepatocytes) remained enigmatic. The gradual improvement of tissue culture systems for HBV has enabled the identification of viral determinants for viral infectivity and facilitated the discovery of the human sodium taurocholate co-transporting polypeptide (hNTCP) as a liver specific receptor of HBV and its satellite, the human Hepatitis Delta Virus (HDV). These findings are currently leading basic and clinical research activities in new directions. (1) Stable hNTCP-expressing cell lines have become a valuable platform to study the full HBV replication cycle from its native template, the cccDNA. (2) The suitability of NTCP complemented cell culture systems for high throughput screening approaches will facilitate identification of novel host factors involved in HBV replication (including those that determine the peculiar host specificity of HBV infection) and will enable identification and development of novel drug candidates for improved therapeutics. (3) Since NTCP is a major host-specific restriction factor for HBV and HDV, hNTCP-expressing animals provide the basis for future susceptible in vivo models. (4) The concept obtained with the entry inhibitor Myrcludex B demonstrates that NTCP is a suitable target for clinical interference with viral entry. This will foster further clinical approaches aiming at curative combination therapies.

Pathogenesis by subviral agents: viroids and hepatitis delta virus

The viroids of plants are the simplest known infectious genetic elements. They have RNA genomes of up to 400 nucleotides in length and no protein encoding capacity. Hepatitis delta virus (HDV), an infectious agent found only in humans co-infected with hepatitis B virus (HBV), is just slightly more complex, with an RNA genome of about 1700 nucleotides, and the ability to express just one small protein. Viroid and HDV RNAs share several features that include circular structure, compact folding, and replication via a rolling-circle mechanism. Both agents were detected because of their obvious pathogenic effects. Their simplicity demands a greater need than conventional RNA or DNA viruses to redirect host components for facilitating their infectious cycle, a need that directly and indirectly incites pathogenic effects. The mechanisms by which these pathogenic effects are produced are the topic of this review. In this context, RNA silencing mediates certain aspects of viroid pathogenesis.

[The return of the hepatitis delta virus]

- There are several regions worldwide with a high prevalence of infection with the hepatitis delta virus (HDV) in hepatitis B virus (HBV) carriers.- Chronic HDV infection is occurring with increasing frequency due to increased immigration.- HDV transmission can take place through the same routes as HBV by simultaneous infection with both viruses (co-infection) or infection of an HBV carrier with HDV (superinfection).- Delta hepatitis is considered as the most severe form of viral hepatitis with a high risk of progression to cirrhosis and hepatocellular carcinoma.- Chronic delta hepatitis is exclusively observed in patients who are HBV carriers.- Pegylated interferon is currently the only registered therapy for patients with delta hepatitis, but leads to a persistent virological response in only a minority of them, and rarely leads to a complete cure.- New antivirals, such as viral entry blockers, prenylation inhibitors and anti-sense oligonucleotides are promising and currently being investigated in phase 2 trials.

Hepatitis viruses exploitation of host DNA methyltransferases functions

Hepatitis B virus (HBV), hepatitis C virus (HCV) and Delta (HDV) infections are a global health burden. With different routes of infection and biology, HBV, HCV and HDV are capable to induce liver cirrhosis and cancer by impinging on epigenetic mechanisms altering host cell's pathways. In the present manuscript, we reviewed the published studies taking into account the relationship between the hepatitis viruses and the DNA methyltransferases proteins.

Hepatitis D virus infection, replication and cross-talk with the hepatitis B virus

Viral hepatitis remains a worldwide public health problem. The hepatitis D virus (HDV) must either coinfect or superinfect with the hepatitis B virus (HBV). HDV contains a small RNA genome (approximately 1.7 kb) with a single open reading frame (ORF) and requires HBV supplying surface antigens (HBsAgs) to assemble a new HDV virion. During HDV replication, two isoforms of a delta antigen, a small delta antigen (SDAg) and a large delta antigen (LDAg), are produced from the same ORF of the HDV genome. The SDAg is required for HDV replication, whereas the interaction of LDAg with HBsAgs is crucial for packaging of HDV RNA. Various clinical outcomes of HBV/HDV dual infection have been reported, but the molecular interaction between HBV and HDV is poorly understood, especially regarding how HBV and HDV compete with HBsAgs for assembling virions. In this paper, we review the role of endoplasmic reticulum stress induced by HBsAgs and the molecular pathway involved in their promotion of LDAg nuclear export. Because the nuclear sublocalization and export of LDAg is regulated by posttranslational modifications (PTMs), including acetylation, phosphorylation, and isoprenylation, we also summarize the relationship among HBsAg-induced endoplasmic reticulum stress signaling, LDAg PTMs, and nuclear export mechanisms in this review.

Host RNA circles and the origin of hepatitis delta virus

Recent reports show that many cellular RNAs are processed to form circular species that are relatively abundant and resistant to host nucleases. In some cases, such circles actually bind host microRNAs. Such depletion of available microRNAs appears to have biological roles; for instance, in homeostasis and disease. These findings regarding host RNA circles support a speculative reappraisal of the origin and mode of replication of hepatitis delta virus, hepatitis delta virus (HDV), an agent with a small circular RNA genome; specifically, it is proposed that in hepatocytes infected with hepatitis B virus (HBV), some viral RNA species are processed to circular forms, which by a series of chance events lead to an RNA that can be both replicated by host enzymes and assembled, using HBV envelope proteins, to form particles some of which are infectious. Such a model also may provide some new insights into the potential pathogenic potential of HDV infections. In return, new insights into HDV might provide information leading to a better understanding of the roles of the host RNA circles.

Virus entry mediated by hepatitis B virus envelope proteins

Hepatitis B virus (HBV), a major cause of human liver disease worldwide, encodes three envelope proteins needed for the attachment and entry of the virus into susceptible host cells. A second virus, hepatitis delta virus, which is known to enhance liver disease in HBV infected patients, diverts the same HBV envelope proteins to achieve its own assembly and infection. In the lab, lentiviral vectors based on human immunodeficiency virus type 1 can be assembled using the HBV envelope proteins, and will similarly infect susceptible cells. This article provides a partial review and some personal reflections of how these three viruses infect and of how recipient cells become susceptible, along with some consideration of questions that remain to be answered.

High prevalence and significance of hepatitis D virus infection among treatment-naïve HBsAg-positive patients in Northern Vietnam

Background

Hepatitis D virus (HDV) infection is considered to cause more severe hepatitis than hepatitis B virus (HBV) monoinfection. With more than 9.5 million HBV-infected people, Vietnam will face an enormous health burden. The prevalence of HDV in Vietnamese HBsAg-positive patients is speculative. Therefore, we assessed the prevalence of HDV in Vietnamese patients, determined the HDV-genotype distribution and compared the findings with the clinical outcome.

Methods

266 sera of well-characterized HBsAg-positive patients in Northern Vietnam were analysed for the presence of HDV using newly developed HDV-specific RT-PCRs. Sequencing and phylogenetic analysis were performed for HDV-genotyping.

Results

The HDV-genome prevalence observed in the Vietnamese HBsAg-positive patients was high with 15.4% while patients with acute hepatitis showed 43.3%. Phylogenetic analysis demonstrated a predominance of HDV-genotype 1 clustering in an Asian clade while HDV-genotype 2 could be also detected. The serum aminotransferase levels (AST, ALT) as well as total and direct bilirubin were significantly elevated in HDV-positive individuals (p<0.05). HDV loads were mainly low (<300 to 4.108 HDV-copies/ml). Of note, higher HDV loads were mainly found in HBV-genotype mix samples in contrast to single HBV-infections. In HBV/HDV-coinfections, HBV loads were significantly higher in HBV-genotype C in comparison to HBV-genotype A samples (p<0.05).

Conclusion

HDV prevalence is high in Vietnamese individuals, especially in patients with acute hepatitis B. HDV replication activity showed a HBV-genotype dependency and could be associated with elevated liver parameters. Besides serological assays molecular tests are recommended for diagnosis of HDV. Finally, the high prevalence of HBV and HDV prompts the urgent need for HBV-vaccination coverage.

Identification of a binding site for ASF/SF2 on an RNA fragment derived from the hepatitis delta virus genome

The hepatitis delta virus (HDV) is a small (∼1700 nucleotides) RNA pathogen which encodes only one open reading frame. Consequently, HDV is dependent on host proteins to replicate its RNA genome. Recently, we reported that ASF/SF2 binds directly and specifically to an HDV-derived RNA fragment which has RNA polymerase II promoter activity. Here, we localized the binding site of ASF/SF2 on the HDV RNA fragment by performing binding experiments using purified recombinant ASF/SF2 combined with deletion analysis and site-directed mutagenesis. In addition, we investigated the requirement of ASF/SF2 for HDV RNA replication using RNAi-mediated knock-down of ASF/SF2 in 293 cells replicating HDV RNA. Overall, our results indicate that ASF/SF2 binds to a purine-rich region distant from both the previously published initiation site of HDV mRNA transcription and binding site of RNAP II, and suggest that this protein is not involved in HDV replication in the cellular system used.

[Current concepts of pathogenesis, clinical course and treatment of hepatitis delta (35 years since its discovery)]

Chronic HDV infection is a most serious and rapidly progressing hepatic disease with high risk of liver cirrhosis and hepato cellular carcinoma (HCC). Many aspects of its pathogenesis, virus biology and treatment remain unknown 35 years after the discovery of the disease. HDV is significantly different from HCV and HBV despite common route of infection. HDV as a satellite pathogen realizes its pathological action in an organism with compromised immune system that proved unable to eliminate HBEV. Hepatic lesions induced by HBV create favourable conditions for HDV propagation that causes rapid development of cirrhosis and its complications. The low efficacy of IFN-alpha therapy is due to the properties of HDV that inhibits the immune response. In most cases, decompensation and hepatic insufficiency determine prognosis of and mortality from HDV infection rather than HCC as in HBV and HCV.

Origin of hepatitis delta virus

This article addresses some of the questions relating to how hepatitis delta virus (HDV), an agent so far unique in the animal world, might have arisen. HDV was discovered in patients infected with hepatitis B virus (HBV). It generally makes HBV infections more damaging to the liver. It is a subviral satellite agent that depends upon HBV envelope proteins for its assembly and ability to infect new cells. In other aspects of replication, HDV is both independent of and very different from HBV. In addition, the small single-stranded circular RNA genome of HDV, and its mechanism of replication, demonstrate an increasing number of similarities to the viroids - a large family of helper-independent subviral agents that cause pathogenesis in plants.

[Role of the hepatitis Delta virus on the pathogenesis of hepatic cirrhosis and hepatocellular carcinoma. Recent advances]

Hepatitis Delta virus is a defective RNA virus that requires HBV as helper virus. The two viruses share the same route of transmission, being prevalently transmitted by contaminated blood and body fluids. HDV can infect simultaneously with HBV (coinfection) or in a patient with already established HBV infection (superinfection). A progressive decline in HDV prevalence both as acute or chronic infection has been observed for several years. More recently, several European countries have observed stable HDV prevalence mainly due to migrants from non European countries. Persistent HDV replication has been demonstrated as correlated to cirrhosis development and hepatocellular carcinoma occurrence. Moreover, persistent HDV replication predicts liver related mortality. Early and prolonged treatment may lead to virus eradication, improving long-term prognosis.

Myristoylation signal transfer from the large to the middle or the small HBV envelope protein leads to a loss of HDV particles infectivity

A myristate linked to the N-terminus of the large hepatitis B virus (HBV) envelope protein was found to be required for infectivity of the hepatitis delta virus (HDV). Myristoylation of the large HBV envelope protein being known as indispensable for HBV infectivity, this result further demonstrates the similarities between the HBV and HDV entry pathways. In addition, the transfer of the N-myristoylation signal from the large to the middle or the small HBV envelope protein led in both cases to a loss of HDV infectivity. Hence, it is suggested that viral entry could depend on a physical link, or a spatial association, between the N-terminal receptor-binding polypeptide of the large protein and the myristoyl anchor linked to glycine-2.

Infectivity determinants of the hepatitis B virus pre-S domain are confined to the N-terminal 75 amino acid residues

The N-terminal pre-S domain of the large hepatitis B virus (HBV) envelope protein plays a pivotal role at the initial step of the viral entry pathway. In the present study, the entire pre-S domain was mapped for infectivity determinants, following a reverse-genetics approach and using in vitro infection assays with hepatitis delta virus (HDV) or HBV particles. The results demonstrate that lesions created within the N-terminal 75 amino acids of the pre-S region abrogate infectivity, whereas mutations between amino acids 76 and 113, overlapping the matrix domain, had no effect. In contrast to the results of a recent study (L. Stoeckl, A. Funk, A. Kopitzki, B. Brandenburg, S. Oess, H. Will, H. Sirma, and E. Hildt, Proc. Natl. Acad. Sci. 103:6730-6734, 2006), the deletion of a cell membrane translocation motif (TLM) located between amino acids 148 and 161 at the C terminus of pre-S2 did not interfere with the infectivity of the resulting HDV or HBV mutants. Furthermore, a series of large deletions overlapping the pre-S2 domain were compatible with infectivity, although the efficiency of infection was reduced when the deletions extended to the pre-S1 domain. Overall, the results demonstrate that the activity of the pre-S domain at viral entry solely depends on the integrity of its first 75 amino acids and thus excludes any function of the matrix domain or TLM.

Hepatitis A, B, C, D, E, G: an update

Acute and chronic liver diseases are an assortment of disorders brought to the clinician's attention by abnormal liver function tests or specific signs and symptoms. The differential diagnosis includes disorders that have primary or secondary liver involvement. This paper will be limited to the epidemiology, clinical manifestations, diagnosis, treatment, and prevention of the different viral liver diseases: A, B, C, D, E and G.

[Etiology and pathogenesis of viral hepatitis]

In the strictest sense, the term "viral hepatitis" includes a series of clinical conditions of infectious origin caused by five phylogenetically unrelated human viruses that have developed specific tropism to hepatocytes. In a broader sense, it also includes acute liver diseases due to infection by other viruses that do not display specific liver tropism, but may produce liver disease as a complication of the infection. Hepatitis B and C viruses have, in addition, developed strategies that allow them to establish long-lasting, chronic infections in some patients. Chronic viral hepatitis, liver cirrhosis and primary liver cancer are the main clinical outcomes of these phenomena of viral persistence, which respond to two main mechanisms: induction of immune tolerance in the host, and emergence and selection of viral mutants that are able to escape the immune response.

Hepatitis delta virus

Hepatitis delta virus (HDV) is a sub-viral agent that is dependent for its life cycle on hepatitis B virus (HBV). The help it obtains from HBV is limited to the sharing of envelope proteins. These proteins are needed to facilitate the assembly of the HDV genome into new virus particles, and in turn, to allow the attachment and entry of HDV into new host cells. In other respects, the replication of the small single-stranded circular RNA genome of HDV is independent of HBV. HDV genome replication produces two forms of a RNA-binding protein known as the long and small delta antigens (Ag). All other proteins needed for HDV genome replication, especially the RNA-directed RNA polymerase activity, are provided by the host cell. This mini-review article is a mixture of personal perspective and speculations about the future of HDV research. It starts with a brief overview of HDV and its replication, notes some of the major unresolved questions, and directs the interested reader to more detailed reviews.

Role of the antigenic loop of the hepatitis B virus envelope proteins in infectivity of hepatitis delta virus

The infectious particles of hepatitis B virus (HBV) and hepatitis delta virus (HDV) are coated with the large, middle, and small envelope proteins encoded by HBV. While it is clear that the N-terminal pre-S1 domain of the large protein, which is exposed at the virion surface, is implicated in binding to a cellular receptor at viral entry, the role in infectivity of the envelope protein antigenic loop, also exposed to the virion surface and accessible to neutralizing antibodies, remains to be established. In the present study, mutations were created in the antigenic loop of the three envelope proteins, and the resulting mutants were evaluated for their capacity to assist in the maturation and infectivity of HDV. We observed that short internal combined deletions and insertions, affecting residues 109 to 133 in the antigenic loop, were tolerated for secretion of both subviral HBV particles and HDV virions. However, when assayed for infectivity on primary cultures of human hepatocytes or on the recently described HepaRG cell line, virions carrying deletions between residues 118 and 129 were defective. Single amino acid substitutions in this region revealed that Gly-119, Pro-120, Cys-121, Arg-122, and Cys-124 were instrumental in viral entry. These results demonstrate that in addition to a receptor-binding site previously identified in the pre-S1 domain of the L protein, a determinant of infectivity resides in the antigenic loop of HBV envelope proteins.

Hepatitis D

Hepatitis D virus (HDV) is a small, RNA-containing virus that requires the concomitant presence of Hepatitis B virus (HBV) in an obligate manner for its survival and pathogenicity. HDV infection is very uncommon in Czech Republic. The results of antiviral therapy of hepatitis D patients are not satisfactory. Alpha-interferon (alpha-IFN) in high doses (9-10 MU three times a week for 12 months) is usually recommended.

Denying the wolf access to sheep's clothing

Hepatitis delta virus (HDV) is a cause of acute and chronic liver disease for which no effective therapy is currently available. Previous research has demonstrated that prenylation of the large HDV antigen is essential for viral assembly. A new report describes a novel small animal model for HDV replication and demonstrates that prenylation inhibitors are highly effective at clearing viremia and thus have potential relevance for the treatment of chronic delta hepatitis.

Role of N glycosylation of hepatitis B virus envelope proteins in morphogenesis and infectivity of hepatitis delta virus

Hepatitis delta virus (HDV) particles are coated with the large (L), middle (M), and small (S) hepatitis B virus envelope proteins. In the present study, we constructed glycosylation-defective envelope protein mutants and evaluated their capacity to assist in the maturation of infectious HDV in vitro. We observed that the removal of N-linked carbohydrates on the S, M, and L proteins was tolerated for the assembly of subviral hepatitis B virus (HBV) particles but was partially inhibitory for the formation of HDV virions. However, when assayed on primary cultures of human hepatocytes, virions coated with S, M, and L proteins lacking N-linked glycans were infectious. Furthermore, in the absence of M, HDV particles coated with nonglycosylated S and L proteins retained infectivity. These results indicate that carbohydrates on the HBV envelope proteins are not essential for the in vitro infectivity of HDV.

Inhibition of hepatitis delta virus RNA editing by short inhibitory RNA-mediated knockdown of ADAR1 but not ADAR2 expression

Hepatitis delta virus (HDV) requires host RNA editing at the viral RNA amber/W site. Of the two host genes responsible for RNA editing via deamination of adenosines in double-stranded RNAs, short inhibitory RNA-mediated knockdown of host ADAR1 expression but not that of ADAR2 led to decreased HDV amber/W editing and virus production. Despite substantial sequence and structural variation among the amber/W sites of the three HDV genotypes, ADAR1a was primarily responsible for editing all three. We conclude that ADAR1 is primarily responsible for editing HDV RNA at the amber/W site during HDV infection.

Latest discoveries on the infection and coinfection with hepatitis D virus

HDV is an incomplete virus that has HBV infection as a prerequisite. Superinfection by HDV leads to acute hepatitis and causes progression to liver cirrhosis in a significant proportion of HBsAg carriers. The traditional methods for the diagnosis of HDV infection, such as detection of serum anti-HD antibodies, are sufficient for the clinical diagnosis of delta infection. However, such techniques lack the sensitivity and specificity required to more accurately characterize the nature of HDV infection and to assess the efficacy of therapies. Recent improvements in molecular techniques, such as HDV RNA hybridization and RT-PCR, have provided increased diagnostic precision and a more thorough understanding of the natural course of HDV infection. These advances have enhanced the clinician's ability to accurately evaluate the stage of HDV infection, response to therapy, and occurrence of reinfection after orthotopic liver transplant.

Animal models of hepatitis delta virus infection and disease

Hepatitis delta virus (HDV) is a defective RNA virus with similarities to unusual subviral pathogens of higher plants. It requires hepatitis B virus (HBV) for its replication/transmission, and HBV-infected humans are the only established host. HDV causes both severe acute hepatitis and rapidly progressive chronic disease in some individuals. The HDV life cycle involves remarkable features, such as ribozyme- mediated autocatalytic processes, Pol II-directed RNA synthesis from a single-stranded circular RNA template, and RNA editing. Much of our understanding of the nature of this pathogen derives from experimental studies in the chimpanzee model of HBV infection. The hepadnavirus-infected eastern woodchuck also is capable of supporting HDV replication and offers opportunities for the development of control strategies that might be applicable to human type D hepatitis.

Deleterious effects of hepatitis delta virus replication on host cell proliferation

Hepatitis delta virus (HDV) infection and spread in vivo are dependent upon coinfection by hepatitis B virus (HBV), and dual HDV/HBV infection is frequently more severe than HBV infection alone, raising the possibility that HDV infection may be deleterious to cells. Here we have examined the effects of HDV replication on the long-term growth of cultured cells. Our results show that most cells transfected with HDV cDNA do not give rise to stable cell lines expressing viral antigens or replicative intermediates; in addition, cotransfection of HDV replicons with a plasmid vector expressing a hygromycin resistance marker results in a dose-dependent impairment of hygromycin-resistant colony formation. When cells transfected with replication-competent HDV cDNA are followed prospectively, a progressive decline in viral RNA replication and a steady decrease in the proportion of cells expressing delta antigen are observed. However, in transient transfection assays, no evidence was found to link HDV replication to apoptosis or to cell cycle arrest, nor did HDV replication confer on host cells enhanced sensitivity to inducers of apoptosis. Thus, HDV replication does not appear to be acutely cytotoxic. However, in dividing cells HDV replication is associated with a subtler growth disadvantage, leading to selection in culture for cells displaying diminished HDV expression. This effect would not be expected to cause hepatitis in vivo but might contribute to impaired liver regeneration in the setting of ongoing hepatocellular injury.

Serological and molecular testing in viral hepatitis: an update

The routine serological diagnoses of the three major forms of viral hepatitis - A, B and C - as well as delta hepatitis, are important in the evaluation of acute and chronic viral hepatitis. Increasingly, molecular virology is also being used to evaluate patients with chronic hepatitis C, with genotype and viral load testing to plan therapy.

Hepatitis delta virus: molecular biology, pathogenesis and immunology

Hepatitis delta virus (HDV) is a unique infectious agent which causes severe liver disease in those infected with its helper virus, hepatitis B virus. No effective antiviral therapy for HDV exists. This review covers recent advances in the molecular biology, pathogenesis and immunology of HDV, with an emphasis on potential targets for the development of successful antiviral agents.

The hepatitis alphabet--hepatitis A-G and TTV

During the past three decades the number of viruses known to be capable to inducing liver inflammation has been considerably expanded. This short review gives a quick overview of the virologic characteristics, clinical manifestations, diagnosis, and treatment options. Newer hepatitis viruses such as hepatitis E virus (HEV), hepatitis GB-virus C/hepatitis G virus (GBV-C/HGV), and transfusion-transmitted virus (TTV) are discussed and data concerning their disease-inducing capacity reviewed.

The relationships of chronic hepatitis and cirrhosis to alcohol intake, hepatitis B and C, and delta virus infection: a case-control study in Albania

The present study examined the effect of hepatitis B virus (HBV) and alcohol intake, and the role of hepatitis delta virus (HDV) and hepatitis C virus (HCV) in the aetiology of chronic liver disease in Albania. A total of 106 cases of liver cirrhosis or chronic hepatitis were compared to 195 control patients without these or other liver diseases. Adjusted odds ratios were 52.7 (95% CI 22.7-122) for HBV surface antigen, 26.9 (95% CI 4.9-147) for anti-HCV, 26.2 (95% CI 3-1-221) for anti-HDV, 2.4 (95% CI 1.3-4.4) for lifetime alcohol intake and 2.3 (95% CI 1-5.5) for duration of alcohol intake. Although not significant, an interaction was suggested between HBsAg and anti-HCV and between HBsAg and alcohol intake. Our study underlines the role of hepatitis viruses in the development of chronic liver diseases. Additionally, it suggests that heavy alcohol intake may magnify the effect of HBV on these diseases. HBV vaccination and alcohol abstention appear to be important strategies to reduce the risk of liver cirrhosis and chronic hepatitis in Albania.

Overexpression of hepatitis delta antigen protects insect cells from baculovirus-induced cytolysis

Hepatitis delta virus (HDV) is a human pathogen causing fulminant hepatitis and liver cirrhosis. HDV has a circular single-stranded RNA genome, which encodes only a single protein, hepatitis delta antigen (HDAg), from the antigenomic strand. Although the functional roles of HDAg have been extensively studied, the molecular mechanism of persistent infection and pathogenesis of HDV are not yet understood. Here we report that overexpressed HDAg protects cells from death in baculovirus-infected insect cells. Using both wild-type and recombinant baculovirus-infected insect cells, we have demonstrated that HDAg inhibited wild-type baculovirus-induced cytolysis and thus extended the survival of virus-infected insect cells. By deletion analysis, we show that N-terminal 25 amino acids are essential for this function. From these data, we suggest that HDAg may play a major role in persistent infection of HDV.