Hepadnaviruses, including human hepatitis B virus (HBV), replicate through reverse transcription of an RNA intermediate, the pregenomic RNA (pgRNA). Despite this kinship to retroviruses, there are fundamental differences beyond the fact that hepadnavirions contain DNA instead of RNA. Most peculiar is the initiation of reverse transcription: it occurs by protein-priming, is strictly committed to using an RNA hairpin on the pgRNA, ε, as template, and depends on cellular chaperones; moreover, proper replication can apparently occur only in the specialized environment of intact nucleocapsids. This complexity has hampered an in-depth mechanistic understanding. The recent successful reconstitution in the test tube of active replication initiation complexes from purified components, for duck HBV (DHBV), now allows for the analysis of the biochemistry of hepadnaviral replication at the molecular level. Here we review the current state of knowledge at all steps of the hepadnaviral genome replication cycle, with emphasis on new insights that turned up by the use of such cell-free systems. At this time, they can, unfortunately, not be complemented by three-dimensional structural information on the involved components. However, at least for the ε RNA element such information is emerging, raising expectations that combining biophysics with biochemistry and genetics will soon provide a powerful integrated approach for solving the many outstanding questions. The ultimate, though most challenging goal, will be to visualize the hepadnaviral reverse transcriptase in the act of synthesizing DNA, which will also have strong implications for drug development.

(1) Reversible and non-cell-type specific attachment to cellassociated heparan sulfate proteoglycans.
(2) Specific and probably irreversible binding to an unknown hepatocyte-specific preS1-receptor. This step presumably requires activation of the virus resulting in exposure of the myristoylated N-terminus of the L-protein [1].
(3) Two different entry pathways have been proposed: (3A) endocytosis followed by release of nucleocapsids from
endocytic vesicles; (3B) fusion of the viral envelope at the plasma membrane.
(4) Cytoplasmic release of the viral nucleocapsid containing the relaxed circular partially double stranded DNA (rcDNA) with its covalently linked polymerase.
(5) Transport of the nucleocapsid along microtubules. Accumulation of the capsids at the nuclear envelope facilitates interactions with adaptor proteins of the nuclear pore complex.
(6) Possible trapping of the nucleocapsid in the nuclear basket and release of rcDNA into the nucleoplasm. The mechanisms determining the breakdown of the capsid and the release of the viral DNA genome are unsolved [2].
(7) ‘‘Repair” of the incoming rcDNA: Completion of the plus strand of the rcDNA by the viral polymerase. Removal of the polymerase from the 50-end of the minus strand
DNA. Removal of a short RNA-primer used for the DNAplus strand synthesis. Both processes are mediated by cellular enzymes [3].
(8) cccDNA formation by covalent ligation of both DNA strands (reviewed in [3]). The cccDNA molecule is organized as a chromatin-like structure displaying the typical beads-on-a string arrangement consisting of both histone and non-histone proteins (minichromosome) [4]. The lack of cccDNA in artificial host cells (e.g. hepatocytes of HBV transgenic mice) suggests that host specific factors may regulate cccDNA formation.
(9) Transcription. The cccDNA utilizes the cellular transcriptional machinery to produce all viral RNAs necessary for protein production and viral replication. Both host transcription factors, such as CCAAT/enhancer-binding protein (C/EBP) and hepatocyte nuclear factors (HNF) and viral proteins (core, the regulatory X-protein) regulate this process [4] and may modulate viral gene expression by interacting with the viral promoters of the four major overlapping open reading frames (ORFs): (I) the precore/ core gene, coding for the nucleocapsid protein and for the non-structural, secreted, precore protein, the HBeAg;
(II) the polymerase gene coding for the reverse transcriptase, RNase H and terminal protein domains; (III) the
L-,M-, and S-gene, coding for the three envelope proteins, which are synthesized in frame from different promoters; and (IV) the X gene, coding for the small regulatory X-protein. A correlation between viremia levels and the acetylation status of cccDNA-bound histones has been reported [5], indicating that epigenetic mechanisms can regulate the transcriptional activity of the cccDNA.
(10) All 4 major mRNAs utilize a single common polyadenylation signal. Processing of viral RNAs, nuclear export as well as stabilization of the viral RNAs appears to be exclusively mediated by host factors (i.e. La RNA binding protein).
(11) Translation of the pregenomic RNA (pgRNA) to the core protein and the viral polymerase. The regulatory X-protein and the three envelope proteins are translated from the subgenomic RNAs.
(12) Complex formation of the pgRNA (via its epsilon stemloop structure) with the core protein and the polymerase and self-assembly of an RNA-containing nucleocapsid.
(13) Reverse transcription of the pgRNA followed by plusstrand DNA-synthesis within the nucleocapsid. Maturation of the RNA-containing nucleocapsids to DNA-containing nucleocapsids within the cytoplasm.
(14) DNA-containing nucleocapsids can be either re-imported into the nucleus to form additional cccDNA molecules
(14A) or can be enveloped for secretion (14B). The envelope proteins are co-translationally inserted into the ER membrane, where they bud into the ER lumen, and are secreted by the cell, either as 22 nm subviral envelope particles (SVPs) or as 42 nm infectious virions (Dane particles) if they have enveloped the DNA-containing nucleocapsids before budding. During synthesis of the L-protein, the preS-domains remain cytoplasmically exposed and become myristoylated. At some step after preS-mediated nucleocapsid envelopment translocation across the membrane occurs.
(15) Experiments performed using duck hepatitis B revealed that the majority of cccDNA molecules in infected hepatocytes comes from newly synthesized nucleocapsids. 1–50 cccDNA molecules appear to accumulate per cell, though differences in cccDNA dynamics and efficiency of cccDNA accumulation may exist between HBV and the other hepadnaviruses. Both viral and host factors controlling cccDNA formation and pool size are yet poorly defined. A negativefeedback mechanism suppressing cccDNA amplification might involve the L-protein. As HBV polymerase inhibitors do not directly affect the cccDNA, a decrease in cccDNA levels is supposed to derive from the lack of sufficient recycling of viral nucleocapsids to the nucleus, due to inhibition of viral DNA-synthesis in the cytoplasm, and less incoming viruses from the blood [6].
(16) Compared to virions spherical and filamentous SVPs are secreted in a 103–106-fold excess into the blood of infected individuals. SVPs lack a nucleocapsid and are therefore non-infectious.

KLIMIK Dergisi: KLIMIK Journal; Istanbul29.2 (Aug 2016): 56-59.

Özet
Hepatit B virusu (HBV)’nun replikasyon sırasında oluşturduğu yüksek viral kopya sayısı ve ters transkriptaz enziminin hata düzeltme (“proofreading”) aktivitesinden yoksun olmasına bağlı olarak, HBV genotipleri, subgenotipleri, mutantlar ve rekombinantlar meydana gelmektedir. Günümüze kadar HBV’nin A’dan J’ye kadar 10 farklı genotipi ve 40’a yakın subgenotipi tanımlanmıştır. Kuzeybatı Avrupa, Kuzey Amerika ve Afrika’da genotip A; Asya ülkelerinde genotip B ve C yaygın olarak görülürken; genotip C Doğu ve Güneydoğu Asya ülkelerinde daha baskın olarak görülmektedir. Genotip D, tüm dünya genelinde yaygın olmakla birlikte Akdeniz Bölgesi, Yakın Doğu ve Ortadoğu ülkeleriyle Güney Asya’da daha sık görülmektedir. Batı Afrika’da genotip E; Orta ve Güney Amerika’da genotip F daha baskındır. Genotip G ise Fransa, Almanya ve Amerika’dan bildirilmiştir. Genotip H, Orta Amerika’da bulunmaktadır. Yeni tanımlanan genotip I ise genotip A, C ve G’nin genotipik rekombinasyonu olarak ortaya çıkmış olup Vietnam ve Laos’tan izole edilmiştir. En yeni genotip olan genotip J, Japonya’nın Ryukyu adalarında tanımlanmıştır ve bu genotipin gibon/orangutan genotipleri ve insan genotip C’siyle yakın ilişkisi bulunmaktadır. Bu derlemede, HBV’nin günümüze kadar tanımlanmış genotip ve subgenotipleri, coğrafi yayılımı ve klinik tablolarla ilişkisi gözden geçirilmiştir.

BMC Gastroenterol. 2012 Feb 14;12:14.

Abstract
BACKGROUND:
The aspartate aminotransferase-to-platelet ratio index (APRI), a tool with limited expense and widespread availability, is a promising noninvasive alternative to liver biopsy for detecting hepatic fibrosis. The objective of this study was to systematically review the performance of the APRI in predicting significant fibrosis and cirrhosis in hepatitis B-related fibrosis.
METHODS:
Areas under summary receiver operating characteristic curves (AUROC), sensitivity and specificity were used to examine the accuracy of the APRI for the diagnosis of hepatitis B-related significant fibrosis and cirrhosis. Heterogeneity was explored using meta-regression.
RESULTS:
Nine studies were included in this meta-analysis (n = 1,798). Prevalence of significant fibrosis and cirrhosis were 53.1% and 13.5%, respectively. The summary AUCs of the APRI for significant fibrosis and cirrhosis were 0.79 and 0.75, respectively. For significant fibrosis, an APRI threshold of 0.5 was 84% sensitive and 41% specific. At the cutoff of 1.5, the summary sensitivity and specificity were 49% and 84%, respectively. For cirrhosis, an APRI threshold of 1.0-1.5 was 54% sensitive and 78% specific. At the cutoff of 2.0, the summary sensitivity and specificity were 28% and 87%, respectively. Meta-regression analysis indicated that the APRI accuracy for both significant fibrosis and cirrhosis was affected by histological classification systems, but not influenced by the interval between Biopsy & APRI or blind biopsy.
CONCLUSION:
Our meta-analysis suggests that APRI show limited value in identifying hepatitis B-related significant fibrosis and cirrhosis.

Hepatit B virus (HBV), Hepadnaviridae ailesinden bir DNA virusudur. Ait oldukları Hepadnaviridae ailesinin diğer üyeleri gibi konakları sınırlıdır ve yerleştikleri konakta akut infeksiyon, persistan infeksiyon, fulminant hepatit, siroz ve hepatosellüler karsinom gibi ölümcül hastalıklara neden olurlar (1) .
Dünya nüfusunun yaklaşık yarısı (2 milyar) HBV ile infekte ve yaklaşık 400-500 milyon kifli (%5-15) HBV taşıyıcısıdır. Türkiyede ise HBs Ag seroprevalansı, bölgeden bölgeye göre farklı olmakla birlikte, bu oran % 3.9-12.5 arasında değişmektedir (2) . Her yıl dünyada 50 milyon, A.B.D.’de 1.5 milyon yeni olgu saptanmaktadır. HBV, sigaradan sonra en önemli ikinci kanserojen etkendir. HBV’ye bağlı nedenlerle yıllık ölüm, yaklaşık 1-2 milyon kişidir. HBV, HIV’den 100 kat daha infeksiyözdür. Bulaştırıcı en düşük kan miktarı HIV için 0.1 ml, HBV için 0.00004 ml’dir (3).

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Clinical Microbiology Reviews, July 2007, p. 426-439, Vol. 20, No. 3

SUMMARY
INTRODUCTION
HBV PROTEINS AND REPLICATION
EPIDEMIOLOGY
HBV INFECTION
ANTIVIRAL AGENTS
MOLECULAR ASSAYS IN THE DIAGNOSIS AND MANAGEMENT OF HBV INFECTION
Quantitative HBV DNA Assays: Utility
Molecular Tests for HBV Quantification: Available Assays and Performance Characteristics
HBV Genotyping: Utility
HBV Genotyping Methods
Antiviral Resistance Testing: Utility and Assays
Detection of Core Promoter/Precore Mutations in HBeAg– CHB: Utility and Assays
FUTURE TRENDS IN MOLECULAR DIAGNOSTIC TESTING FOR CHRONIC HEPATITIS B
ACKNOWLEDGMENTS
REFERENCES

Hepatitis B virus (HBV) is an enveloped virus with a small (3.2-kb) partially double-stranded DNA genome that causes acute and chronic infections. The impact of these infections on public health worldwide is enormous, with an estimated prevalence of 2 billion acute infections and 360 million chronic infections globally. This review focuses on chronic hepatitis B and the molecular assays used in its diagnosis and management. Background information, including that about features of the hepatitis B virion, viral replication, and epidemiology of infection, that is important for understanding chronic hepatitis B and molecular diagnostic tests for HBV is provided. To facilitate an understanding of the utility of molecular testing for chronic hepatitis B, the four stages of chronic hepatitis B infection that are currently recognized, as well as an additional entity, occult hepatitis B, that can be diagnosed only by sensitive nucleic acid amplification methods, are reviewed in detail, including available therapeutic agents. The molecular diagnostic content focuses on tests for HBV DNA quantification, genotyping, and mutation detection (including precore/core promoter and antiviral resistance mutations). The discussion of these tests encompasses their current utility and performance characteristics, drawing from current clinical guidelines and other studies from the literature. In recognition of the continual evolution of this field, the final section describes emerging molecular markers with future diagnostic potential.

HEPATOLOGY 2007; 45: 507-39

The following guidelines are an update to previous AASLD guidelines and reflect new knowledge and the licensure of new antiviral agents against HBV. Recommendations in these guidelines pertain to the (1) evaluation of patients with chronic HBV infection, (2) prevention of HBV infection, (3) management of chronically infected persons, and (4) treatment of chronic hepatitis B.

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Adapted from materials by the Hennepin County Community Health Department and the Minnesota Department of Health

Prof. Dr. Ulus Salih AKARCA

The Turkish Journal of Gastroenterology 2008,19 (4),207-230

Like in the rest of the world, hepatitis B virus (HBV) infection is also a major health problem in our country. Approximately 400 million are known to be chronically infected with HBV. About 3.5 millions have evidence of present or past infection (1). Chronically infected patients die of hepatic complications secondary to the disease in 15-40% of cases. The disease shall maintain its importance in future decades despite efficient vaccination (2). Beside its wide prevalence and association with serious morbidity and mortality, the problems encountered in the treatment also make this disease a major health problem. This report will review HBV virology; pathogenesis; route of transmission and epidemiology of the disease; preventive measures; diagnostic methods; screening programs; standard treatment modalities; treatment of special patient populations; and social problems; and offer recommendations in related topics.