Distinct Entry Mechanisms for Nonenveloped and Quasi-Enveloped Hepatitis E Viruses. J Virol. 2016;90:4232-4242. [PMID: 26865708 DOI: 10.1128/jvi.02804-15]

ICTV Virus Taxonomy Profile: Hepeviridae 2022

The family Hepeviridae includes enterically transmitted small quasi-enveloped or non-enveloped positive-sense single-stranded RNA viruses infecting mammals and birds (subfamily Orthohepevirinae) or fish (Parahepevirinae). Hepatitis E virus (genus Paslahepevirus) is responsible for self-limiting acute hepatitis in humans; the infection may become chronic in immunocompromised individuals and extrahepatic manifestations have been described. Avian hepatitis E virus (genus Avihepevirus) causes hepatitis-splenomegaly syndrome in chickens. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Hepeviridae, which is available at www.ictv.global/report/hepeviridae.

Two mutations in the ORF1 of genotype 1 hepatitis E virus enhance virus replication and may associate with fulminant hepatic failure

Hepatitis E virus (HEV) infection in pregnant women has a high incidence of developing fulminant hepatic failure (FHF) with significant mortality. Multiple amino acid changes in genotype 1 HEV (HEV-1) are reportedly linked to FHF clinical cases, but experimental confirmation of the roles of these changes in FHF is lacking. By utilizing the HEV-1 indicator replicon and infectious clone, we generated 11 HEV-1 single mutants, each with an individual mutation, and investigated the effect of these mutations on HEV replication and infection in human liver cells. We demonstrated that most of the mutations actually impaired HEV-1 replication efficiency compared with the wild type (WT), likely due to altered physicochemical properties and structural conformations. However, two mutations, A317T and V1120I, significantly increased HEV-1 replication. Notably, these two mutations simultaneously occurred in 100% of 21 HEV-1 variants from patients with FHF in Bangladesh. We further created an HEV-1 A317T/V1120I double mutant and found that it greatly enhanced HEV replication, which may explain the rapid viral replication and severe disease. Furthermore, we tested the effect of these FHF-associated mutations on genotype 3 HEV (HEV-3) replication and found that all the mutants had a reduced level of replication ability and infectivity, which is not unexpected due to distinct infection patterns between HEV-1 and HEV-3. Additionally, we demonstrated that these FHF-associated mutations do not appear to alter their sensitivity to ribavirin (RBV), suggesting that ribavirin remains a viable option for antiviral therapy for patients with FHF. The results have important implications for understanding the mechanism of HEV-1-associated FHF.

A ribavirin-induced ORF2 single-nucleotide variant produces defective hepatitis E virus particles with immune decoy function

Hepatitis E virus (HEV) has increasing prevalence worldwide. However, little is known about the impact of single-nucleotide variants (SNV) on the replication cycle. Here, we report a ribavirin-induced open reading frame 2 (ORF2) SNV that demonstrats reduced RNA copies released in the supernatant and an impairment in the production of infectious particles. Furthermore, the P79S variant displays an altered subcellular distribution of the ORF2 protein and is able to impair antibody-mediated neutralization of HEV in a competition assay potentially acting as an immune decoy. These findings provide insights in understanding the biology of circulating HEV variants and may guide development of personalized antiviral strategies in the future.

Hepatitis E virus (HEV) is the causative agent of hepatitis E in humans and is the leading cause of enterically transmitted viral hepatitis worldwide. Ribavirin (RBV) is currently the only treatment option for many patients; however, cases of treatment failures or posttreatment relapses have been frequently reported. RBV therapy was shown to be associated with an increase in HEV genome heterogeneity and the emergence of distinct HEV variants. In this study, we analyzed the impact of eight patient-derived open reading frame 2 (ORF2) single-nucleotide variants (SNVs), which occurred under RBV treatment, on the replication cycle and pathogenesis of HEV. The parental HEV strain and seven ORF2 variants showed comparable levels of RNA replication in human hepatoma cells and primary human hepatocytes. However, a P79S ORF2 variant demonstrated reduced RNA copy numbers released in the supernatant and an impairment in the production of infectious particles. Biophysical and biochemical characterization revealed that this SNV caused defective, smaller HEV particles with a loss of infectiousness. Furthermore, the P79S variant displayed an altered subcellular distribution of the ORF2 protein and was able to interfere with antibody-mediated neutralization of HEV in a competition assay. In conclusion, an SNV in the HEV ORF2 could be identified that resulted in altered virus particles that were noninfectious in vitro and in vivo, but could potentially serve as immune decoys. These findings provide insights in understanding the biology of circulating HEV variants and may guide development of personalized antiviral strategies in the future.

Structure Prediction and Analysis of Hepatitis E Virus Non-Structural Proteins from the Replication and Transcription Machinery by AlphaFold2

Hepatitis E virus (HEV) is a major cause of acute viral hepatitis in humans globally. Considered for a long while a public health issue only in developing countries, the HEV infection is now a global public health concern. Most human infections are caused by the HEV genotypes 1, 2, 3 and 4 (HEV-1 to HEV-4). Although HEV-3 and HEV-4 can evolve to chronicity in immunocompromised patients, HEV-1 and HEV-2 lead to self-limited infections. HEV has a positive-sense single-stranded RNA genome of ~7.2 kb that is translated into a large pORF1 replicative polyprotein, essential for the viral RNA genome replication and transcription. Unfortunately, the composition and structure of these replicases are still unknown. The recent release of the powerful machine-learning protein structure prediction software AlphaFold2 (AF2) allows us to accurately predict the structure of proteins and their complexes. Here, we used AF2 with the replicase encoded by the polyprotein pORF1 of the human-infecting HEV-3. The boundaries and structures reveal five domains or nonstructural proteins (nsPs): the methyltransferase, Zn-binding domain, macro, helicase, and RNA-dependent RNA polymerase, reliably predicted. Their substrate-binding sites are similar to those observed experimentally for other related viral proteins. Precisely knowing enzyme boundaries and structures is highly valuable to recombinantly produce stable and active proteins and perform structural, functional and inhibition studies.

Using codon usage analysis to speculate potential animal hosts of hepatitis E virus: An exploratory study

There has been an increase in the reported number of animals worldwide that carry the hepatitis E virus (HEV). This study aimed to explore potential animal hosts for HEV through codon usage analysis. Full-length HEV sequences of six genotypes as well as codon usage of potential animal hosts were collected. Moreover, nucleotide composition and codon usage bias were compared across HEV genotypes and animal hosts. Based on the analysis for human HEV-1 and humans, the results were basically consistent with epidemiology evidence. Among 17 potential animal hosts, all HEV genotypes exhibited a preference for guanine/cytosine in the third position of synonymous codons. Furthermore, non-human primates and humans have large high-frequency codons identical to HEV in addition to a high correlation of codon fraction with HEV. Some animals in close contact with humans showed high preference for HEV, including cattle, dogs, and rats with HEV-A, cats, dogs, and swine with HEV-C1. Codon usage bias has limited efficiency in determining the hosts for HEV, but it may provide indicative clues for potential animal hosts when combined with experimental and epidemiological evidence.

The encephalomyocarditis virus Leader promotes the release of virions inside extracellular vesicles via the induction of secretory autophagy

Naked viruses can escape host cells before the induction of lysis via release in extracellular vesicles (EVs). These nanosized EVs cloak the secreted virus particles in a host-derived membrane, which alters virus-host interactions that affect infection efficiency and antiviral immunity. Currently, little is known about the viral and host factors regulating this form of virus release. Here, we assessed the role of the encephalomyocarditis virus (EMCV) Leader protein, a 'viral security protein' that subverts the host antiviral response. EV release upon infection with wildtype virus or a Leader-deficient mutant was characterized at the single particle level using high-resolution flow cytometry. Inactivation of the Leader abolished EV induction during infection and strongly reduced EV-enclosed virus release. We demonstrate that the Leader promotes the release of virions within EVs by stimulating a secretory arm of autophagy. This newly discovered role of the EMCV Leader adds to the variety of mechanisms via which this protein affects virus-host interactions. Moreover, these data provide first evidence for a crucial role of a non-structural viral protein in the non-lytic release of picornaviruses via packaging in EVs.

Codon Usage of Hepatitis E Viruses: A Comprehensive Analysis

Hepatitis E virus (HEV) is an emerging zoonotic pathogen with multiple species and genotypes, which may be classified into human, animal, and zoonotic HEV. Codon usage bias of HEV remained unclear. This study aims to characterize the codon usage of HEV and elucidate the main drivers influencing the codon usage bias. A total of seven HEV genotypes, HEV-1 (human HEV), HEV-3 and HEV-4 (zoonotic HEV), HEV-8, HEV-B, HEV-C1, and HEV-C2 (emerging animal HEV), were included in the study. Complete coding sequences, ORF1, ORF2, and ORF3, were accordingly obtained in the GenBank. Except for HEV-8, the other six genotypes tended to use codons ending in G/C. Based on the analysis of relatively synonymous codon usage (RSCU) and principal component analysis (PCA), codon usage bias was determined for HEV genotypes. Codon usage bias differed widely across human, zoonotic, and animal HEV genotypes; furthermore, it varied within certain genotypes such as HEV-4, HEV-8, and HEV-C1. In addition, dinucleotide abundance revealed that HEV was affected by translation selection to form a unique dinucleotide usage pattern. Moreover, parity rule 2 analysis (PR2), effective codon number (ENC)-plot, and neutrality analysis were jointly performed. Natural selection played a leading role in forming HEV codon usage bias, which was predominant in HEV-1, HEV-3, HEV-B and HEV-C1, while affected HEV-4, HEV-8, and HEV-C2 in combination with mutation pressure. Our findings may provide insights into HEV evolution and codon usage bias.

Hepatitis E virus infects brain microvascular endothelial cells, crosses the blood-brain barrier, and invades the central nervous system

Hepatitis E virus (HEV) causes not only acute and chronic hepatitis but also neurological disorders. To delineate the mechanism of HEV-associated neurological diseases, we showed that both quasi-enveloped and nonenveloped HEVs can cross the blood–brain barrier model in a tumor necrosis factor alpha (TNF-α)-independent manner and productively infect brain microvascular endothelial cells in vitro. Furthermore, we showed that HEV was detected in brain and spinal cord from HEV-infected pigs and that pigs with detectable HEV in central nervous system (CNS) tissues had histological lesions in brain and spinal cord and significantly higher levels of proinflammatory cytokines TNF-α and interleukin 18 than pigs without detectable HEV in CNS tissues. The results shed light on a potential mechanism of HEV-associated neuroinvasion.

Hepatitis E virus (HEV) is an important but understudied zoonotic virus causing both acute and chronic viral hepatitis. A proportion of HEV-infected individuals also developed neurological diseases such as Guillain–Barré syndrome, neuralgic amyotrophy, encephalitis, and myelitis, although the mechanism remains unknown. In this study, by using an in vitro blood–brain barrier (BBB) model, we first investigated whether HEV can cross the BBB and whether the quasi-enveloped HEV virions are more permissible to the BBB than the nonenveloped virions. We found that both quasi-enveloped and nonenveloped HEVs can similarly cross the BBB and that addition of proinflammatory cytokine tumor necrosis factor alpha (TNF-α) has no significant effect on the ability of HEV to cross the BBB in vitro. To explore the possible mechanism of HEV entry across the BBB, we tested the susceptibility of human brain microvascular endothelial cells lining the BBB to HEV infection and showed that brain microvascular endothelial cells support productive HEV infection. To further confirm the in vitro observation, we conducted an experimental HEV infection study in pigs and showed that both quasi-enveloped and nonenveloped HEVs invade the central nervous system (CNS) in pigs, as HEV RNA was detected in the brain and spinal cord of infected pigs. The HEV-infected pigs with detectable viral RNA in CNS tissues had histological lesions in brain and spinal cord and significantly higher levels of proinflammatory cytokines TNF-α and interleukin 18 than the HEV-infected pigs without detectable viral RNA in CNS tissues. The findings suggest a potential mechanism of HEV-associated neuroinvasion.

Bile acids promote the caveolae-associated entry of swine acute diarrhea syndrome coronavirus in porcine intestinal enteroids

Intestinal microbial metabolites have been increasingly recognized as important regulators of enteric viral infection. However, very little information is available about which specific microbiota-derived metabolites are crucial for swine enteric coronavirus (SECoV) infection in vivo. Using swine acute diarrhea syndrome (SADS)-CoV as a model, we were able to identify a greatly altered bile acid (BA) profile in the small intestine of infected piglets by untargeted metabolomic analysis. Using a newly established ex vivo model–the stem cell-derived porcine intestinal enteroid (PIE) culture–we demonstrated that certain BAs, cholic acid (CA) in particular, enhance SADS-CoV replication by acting on PIEs at the early phase of infection. We ruled out the possibility that CA exerts an augmenting effect on viral replication through classic farnesoid X receptor or Takeda G protein-coupled receptor 5 signaling, innate immune suppression or viral attachment. BA induced multiple cellular responses including rapid changes in caveolae-mediated endocytosis, endosomal acidification and dynamics of the endosomal/lysosomal system that are critical for SADS-CoV replication. Thus, our findings shed light on how SECoVs exploit microbiome-derived metabolite BAs to swiftly establish viral infection and accelerate replication within the intestinal microenvironment.

Bile acids (BAs), a commonly studied category of microbial metabolites, have long been acknowledged to have proviral or antiviral activities. Recent studies using different swine enteric coronaviruses (SECoVs) showed that BA play an important role in regulating viral replication in vitro. A mechanistic understanding of how BA regulates SECoV replication in small intestinal enterocytes is lacking. Herein, we utilized an emerging highly pathogenic SECoV, swine acute diarrhea syndrome (SADS)-CoV, which possesses the potential for zoonotic transmission, to investigate the crucial role of BA in modulating viral replication in porcine intestinal enteroids (PIEs). Our observations explain how BAs acts on epithelial cells to enhance SADS-CoV replication by inducing caveolae-mediated endocytosis and endosomal acidification, altering the dynamics of viral trafficking through the cellular endosomal/lysosomal system. Our results shed light on the role of BAs in the rapid establishment of SECoV infection within the intestinal microenvironment.

Independent Evaluation of Cell Culture Systems for Hepatitis E Virus

Hepatitis E virus (HEV) infection in humans is primarily caused by genotypes within Paslahepevirus species balayani (HEV-A). Rocahepevirus species ratti (HEV-C1, otherwise known as rat HEV) can also infect humans. HEV grows poorly in cell culture. Recent studies have reported that hyper-confluent cell layers, amphotericin B, MgCl₂, progesterone, and dimethyl sulfoxide (DMSO) increase HEV yield in vitro. Here, we describe an independent evaluation of the effectiveness of these modifications in improving the yield of HEV-A genotype 4 (HEV-A4) and HEV-C1 from clinical samples in PLC/PRF/5 cells. We found that amphotericin B, MgCl₂, and DMSO increased HEV yield from high-viral-load patient stool samples, while progesterone was not effective. Yield of HEV-C1 was lower than HEV-A4 across all medium conditions, but was boosted by DMSO. HEV-A4 could be maintained for over 18 months in amphotericin B- and MgCl₂-containing medium, with the demonstration of viral antigen in supernatants and infected cells. We also evaluated various protocols to remove pseudo-envelopes from cell culture-derived HEV. Treating cell culture supernatant with NP-40 was the most effective. Our findings identify key modifications that boost HEV growth in vitro and illustrate the importance of independent verification of such studies using diverse HEV variants and cell lines.

Stability of Hepatitis E Virus After Drying on Different Surfaces

The hepatitis E virus (HEV) causes acute and chronic hepatitis in humans. The zoonotic HEV genotype 3 is mainly transmitted by consumption of contaminated food produced from infected animals. However, transmission via contaminated surfaces has also to be considered. Here, the genotype 3c strain 47832c was dried on steel, wood, plastics and ceramics, stored at 23 °C or 3 °C for up to 8 weeks and remaining infectivity was titrated on cell culture. During the drying process, only a mean 0.2 log₁₀ decrease of HEV infectivity was observed. At 23 °C, remaining infectious virus was detected until week 4 on most surfaces, but HEV was completely inactivated (> 4 log₁₀ decrease) after 8 weeks. At 3 °C, HEV was detectable up to 8 weeks on most surfaces, with an average 2.3 log₁₀ decrease. HEV showed the highest stability on plastics, which was lower on ceramics and steel, and lowest on wood. The addition of bovine serum albumin mimicking high protein load had only a slight stabilizing effect. In conclusion, HEV shows a high stability against drying and subsequent storage on different surfaces. Strict application of hygienic measures during food production is therefore crucial in order to prevent HEV persistence on surfaces and subsequent cross-contamination.

Reovirus infection is regulated by NPC1 and endosomal cholesterol homeostasis

Cholesterol homeostasis is required for the replication of many viruses, including Ebola virus, hepatitis C virus, and human immunodeficiency virus-1. Niemann-Pick C1 (NPC1) is an endosomal-lysosomal membrane protein involved in cholesterol trafficking from late endosomes and lysosomes to the endoplasmic reticulum. We identified NPC1 in CRISPR and RNA interference screens as a putative host factor for infection by mammalian orthoreovirus (reovirus). Following internalization via clathrin-mediated endocytosis, the reovirus outer capsid is proteolytically removed, the endosomal membrane is disrupted, and the viral core is released into the cytoplasm where viral transcription, genome replication, and assembly take place. We found that reovirus infection is significantly impaired in cells lacking NPC1, but infection is restored by treatment of cells with hydroxypropyl-β-cyclodextrin, which binds and solubilizes cholesterol. Absence of NPC1 did not dampen infection by infectious subvirion particles, which are reovirus disassembly intermediates that bypass the endocytic pathway for infection of target cells. NPC1 is not required for reovirus attachment to the plasma membrane, internalization into cells, or uncoating within endosomes. Instead, NPC1 is required for delivery of transcriptionally active reovirus core particles from endosomes into the cytoplasm. These findings suggest that cholesterol homeostasis, ensured by NPC1 transport activity, is required for reovirus penetration into the cytoplasm, pointing to a new function for NPC1 and cholesterol homeostasis in viral infection.

Genetic screens are useful strategies to identify host factors required for viral infection. NPC1 was identified in independent CRISPR and RNA interference screens as a putative host factor required for reovirus replication. We discovered that NPC1-mediated cholesterol transport is dispensable for reovirus attachment, internalization, and disassembly but required for penetration of the viral disassembly intermediate from late endosomes into the cytoplasm. These findings uncover an essential function for cholesterol in the entry of reovirus and raise the possibility that cholesterol homeostasis regulates the entry of other viruses that penetrate late endosomes to initiate replication.

Avian Hepatitis E Virus ORF2 Protein Interacts with Rap1b to Induce Cytoskeleton Rearrangement That Facilitates Virus Internalization

Avian hepatitis E virus (HEV) causes liver diseases and multiple extrahepatic disorders in chickens. However, the mechanisms involved in avian HEV entry remain elusive. Herein, we identified the RAS-related protein 1b (Rap1b) as a potential HEV-ORF2 protein interacting candidate. Experimental infection of chickens and cells with an avian HEV isolate from China (CaHEV) led to upregulated expression and activation of Rap1b both in vivo and in vitro. By using CaHEV capsid as mimic of virion to treat cell in vitro, it appears that the interaction between the viral capsid and Rap1b promoted cell membrane recruitment of the downstream effector Rap1-interacting molecule (RIAM). In turn, RIAM further enhanced Talin-1 membrane recruitment and retention, which led to the activation of integrin α5/β1, as well as integrin-associated membrane protein kinases, including focal adhesion kinase (FAK). Meanwhile, FAK activation triggered activation of downstream signaling molecules, such as Ras-related C3 botulinum toxin substrate 1 RAC1 cell division cycle 42 (CDC42), p21-activated kinase 1 (PAK1), and LIM domain kinase 1 (LIMK1). Finally, F-actin rearrangement induced by Cofilin led to the formation of lamellipodia, filopodia, and stress fibers, contributes to plasma membrane remodeling, and might enhance CaHEV virion internalization. In conclusion, our data suggested that Rap1b activation was triggered during CaHEV infection and appeared to require interaction between CaHEV-ORF2 and Rap1b, thereby further inducing membrane recruitment of Talin-1. Membrane-bound Talin-1 then activates key Integrin-FAK-Cofilin cascades involved in modulation of actin kinetics, and finally leads to F-actin rearrangement and membrane remodeling to potentially facilitate internalization of CaHEV virions into permissive cells. IMPORTANCE Rap1b is a multifunctional protein that is responsible for cell adhesion, growth, and differentiation. The inactive form of Rap1b is phosphorylated and distributed in the cytoplasm, while active Rap1b is prenylated and loaded with GTP to the cell membrane. In this study, the activation of Rap1b was induced during the early stage of avian HEV infection under the regulation of PKA and SmgGDS. Continuously activated Rap1b recruited its effector RIAM to the membrane, thereby inducing the membrane recruitment of Talin-1 that led to the activation of membrane α5/β1 integrins. The triggering of the signaling pathway-associated Integrin α5/β1-FAK-CDC42&RAC1-PAK1-LIMK1-Cofilin culminated in F-actin polymerization and membrane remodeling that might promote avian HEV virion internalization. These findings suggested a novel mechanism that is potentially utilized by avian HEV to invade susceptible cells.

Development of recombinant infectious hepatitis E virus harboring the nanoKAZ gene and its application in drug screening

Hepatitis E virus (HEV) is a quasi-enveloped virus with a single-stranded positive-sense RNA genome belonging to family Hepeviridae. Studies on molecular aspects of HEV and drug screening have benefited from the discovery of bioluminescent reporter genes. However, the stability of large foreign genes is difficult to maintain after insertion into the viral genome. Currently, ribavirin is used to treat HEV-infected patients who require antiviral therapy. This has several major drawbacks. Thus, the development of novel anti-HEV drugs is of great importance. We developed a system consisting of recombinant infectious HEV harboring small luciferase gene (nanoKAZ) in the hypervariable region (HVR) of the open reading frame 1 (ORF1) (HEV-nanoKAZ). It replicated efficiently in cultured cells, was genetically stable, and had morphological characteristics similar to the parental virus. Both membrane-associated (eHEV-nanoKAZ) and membrane-unassociated (neHEV-nanoKAZ) particles were infectious. HEV particles circulating in the blood stream and attaching to hepatocytes in HEV-infected patients are membrane-associated, thus, eHEV-nanoKAZ was applied in drug screening. The eHEV-nanoKAZ system is able to cover at least the inhibitor of HEV entry and inhibitor of HEV RNA replication. Four drugs with anti-HEV activity were identified. Their effectiveness in cultured cells was confirmed in naïve and HEV-producing PLC/PRF/5 cells. Two hit drugs (azithromycin and ritonavir) strongly inhibited HEV production in culture supernatants, as well as intracellular expression of ORF2 protein, and may therefore be candidate novel anti-HEV drugs. The HEV-nanoKAZ system was developed and applied in drug screening, and is expected to be useful for investigating the HEV life cycle. IMPORTANCE Bioluminescent reporter viruses are essential tools in molecular virological research. It has been widely used to investigate viral life cycles and in the development of antiviral drugs. For drug screening, the use of a bioluminescent reporter virus helps shorten the time required to perform the assay. A system, consisting of recombinant infectious HEV harboring the nanoKAZ gene in the HVR of ORF1 (HEV-nanoKAZ), was developed in this study, and was successfully applied to drug screening in which four hit drugs with anti-HEV activity were identified. The results of this study provide evidence supporting the use of this system in more variable HEV studies. In addition, both forms of viral particles (eHEV-nanoKAZ and neHEV-nanoKAZ) are infectious, which will enable their application in HEV studies requiring both forms of viral particles, such as in the investigation of unknown HEV receptors and the elucidation of host factors important for HEV entry.

Recapitulating hepatitis E virus-host interactions and facilitating antiviral drug discovery in human liver-derived organoids

Hepatotropic viruses naturally have narrow host and tissue tropisms, challenging the development of robust experimental models. The advent of organoid technology provides a unique opportunity for moving the field forward. Here, we demonstrate that three-dimensional cultured organoids from fetal and adult human liver with cholangiocyte or hepatocyte phenotype support hepatitis E virus (HEV) replication. Inoculation with infectious HEV particles demonstrates that human liver–derived organoids support the full life cycle of HEV infection. By directing organoids toward polarized monolayers in a transwell system, we observed predominantly apical secretion of HEV particles. Genome-wide transcriptomic and tRNAome analyses revealed robust host responses triggered by viral replication. Drug screening in organoids identified brequinar and homoharringtonine as potent HEV inhibitors, which are also effective against the ribavirin resistance variant harboring G1634R mutation. Thus, successful recapitulation of HEV infection in liver-derived organoids shall facilitate the study of virus-host interactions and development of antiviral therapies.

Transfusion-transmitted hepatitis E: What we know so far?

Hepatitis E virus (HEV) is a major cause of viral hepatitis globally. There is growing concern about transfusion-transmitted HEV (TT-HEV) as an emerging global health problem. HEV can potentially result in chronic infection in immunocompromised patients, leading to a higher risk of liver cirrhosis and even death. Between 0.0013% and 0.281% of asymptomatic blood donors around the world have HEV viremia, and 0.27% to 60.5% have anti-HEV immunoglobulin G. HEV is infectious even at very low blood concentrations of the virus. Immunosuppressed patients who develop persistent hepatitis E infection should have their immunosuppressant regimen reduced; ribavirin may be considered as treatment. Pegylated interferon can be considered in those who are refractory or intolerant to ribavirin. Sofosbuvir, a nucleotide analog, showed modest antiviral activity in some clinical studies but sustained viral response was not achieved. Therefore, rescue treatment remains an unmet need. The need for HEV screening of all blood donations remains controversial. Universal screening has been adopted in some countries after consideration of risk and resource availability. Various pathogen reduction methods have also been proposed to reduce the risk of TT-HEV. Future studies are needed to define the incidence of transmission through transfusion, their clinical features, outcomes and prognosis.

Structural aspects of hepatitis E virus

Hepatitis E virus (HEV) is a leading cause of acute hepatitis worldwide. Hepatitis E is an enterically transmitted zoonotic disease that causes large waterborne epidemic outbreaks in developing countries and has become an increasing public-health concern in industrialized countries. In this setting, the infection is usually acute and self-limiting in immunocompetent individuals, although chronic cases in immunocompromised patients have been reported, frequently associated with several extrahepatic manifestations. Moreover, extrahepatic manifestations have also been reported in immunocompetent individuals with acute HEV infection. HEV belongs to the alphavirus-like supergroup III of single-stranded positive-sense RNA viruses, and its genome contains three partially overlapping open reading frames (ORFs). ORF1 encodes a nonstructural protein with eight domains, most of which have not been extensively characterized: methyltransferase, Y domain, papain-like cysteine protease, hypervariable region, proline-rich region, X domain, Hel domain, and RNA-dependent RNA polymerase. ORF2 and ORF3 encode the capsid protein and a multifunctional protein believed to be involved in virion release, respectively. The novel ORF4 is only expressed in HEV genotype 1 under endoplasmic reticulum stress conditions, and its exact function has not yet been elucidated. Despite important advances in recent years, the biological and molecular processes underlying HEV replication remain poorly understood, primarily due to a lack of detailed information about the functions of the viral proteins and the mechanisms involved in host-pathogen interactions. This review summarizes the current knowledge concerning HEV proteins and their biological properties, providing updated detailed data describing their function and focusing in detail on their structural characteristics. Furthermore, we review some unclear aspects of the four proteins encoded by the ORFs, highlighting the current key information gaps and discussing potential novel experimental strategies for shedding light on those issues.

The Capsid (ORF2) Protein of Hepatitis E Virus in Feces Is C-Terminally Truncated

The hepatitis E virus (HEV) is a causative agent of hepatitis E. HEV virions in circulating blood and culture media are quasi-enveloped, while those in feces are nonenveloped. The capsid (ORF2) protein associated with an enveloped HEV virion is reported to comprise the translation product of leucine 14/methionine 16 to 660 (C-terminal end). However, the nature of the ORF2 protein associated with fecal HEV remains unclear. In the present study, we compared the molecular size of the ORF2 protein among fecal HEV, cell-culture-generated HEV (HEVcc), and detergent-treated protease-digested HEVcc. The ORF2 proteins associated with fecal HEV were C-terminally truncated and showed the same size as those of the detergent-treated protease-digested HEVcc virions (60 kDa), in contrast to those of the HEVcc (68 kDa). The structure prediction of the ORF2 protein (in line with previous studies) demonstrated that the C-terminal region (54 amino acids) of an ORF2 protein is in flux, suggesting that proteases target this region. The nonenveloped nondigested HEV structure prediction indicates that the C-terminal region of the ORF2 protein moves to the surface of the virion and is unnecessary for HEV infection. Our findings clarify the maturation of nonenveloped HEV and will be useful for studies on the HEV lifecycle.

[Viral hepatitis A to E: prevalence, pathogen characteristics, and pathogenesis]

Bei der viralen Hepatitis handelt es sich um eine akute oder chronische Entzündung der Leber, die durch verschiedene Viren verursacht wird. Weltweit leiden derzeit ca. 325 Mio. Menschen an der chronischen Form. Jährlich versterben insgesamt ca. 1,6 Mio. an den Folgen einer viralen Hepatitis. Die Hepatitisviren werden in 5 Erregergruppen unterteilt, die mit den Buchstaben A bis E bezeichnet werden (HAV–HEV). Diese unterscheiden sich in Phylogenie, Übertragung, Epidemiologie, Wirtsspezifität, Lebenszyklus, Struktur und in speziellen Aspekten der Pathogenese.

Das strikt humanpathogene HAV, Teil der Familie Picornaviridae, induziert meist nur akute Hepatitiden und ist primär in Entwicklungsländern verbreitet. Das den Hepeviridae zugeordnete HEV beschreibt eine ähnliche Epidemiologie, ist jedoch durch sein zoonotisches Potenzial auch in Industrienationen weitverbreitet und kann zusätzlich eine chronische Erkrankung induzieren. Eine Chronifizierung tritt ebenso bei dem weltweit verbreiteten HBV (Hepadnaviridae) auf, dessen Satellitenvirus HDV (Kolmioviridae) das vorhandene kanzerogene Potenzial noch einmal erhöht. Das ebenfalls weltweit verbreitete HCV (Flaviviridae) birgt ein äußerst hohes Risiko der Chronifizierung und somit ebenfalls ein stark erhöhtes, kanzerogenes Potenzial.

Die Erreger der viralen Hepatitis unterscheiden sich in ihren Eigenschaften und Lebenszyklen. Eine differenzierte Betrachtung im Hinblick auf Epidemiologie, Nachweismethoden und Prävention ist daher angezeigt. Obwohl robuste Therapien, und im Falle einzelner Erreger auch Vakzine, vorhanden sind, muss die Forschung insbesondere in Hinblick auf die armutsassoziierten Erreger erheblich vorangetrieben werden.

The Role of Exosomes in Viral Hepatitis and Its Associated Liver Diseases

Exosomes, the important carriers between cells, can carry proteins, micro ribonucleic acids (miRNAs), long non-coding RNAs (lncRNAs) and other molecules to mediate cellular information transduction. They also play an important role in the pathogenesis, prognosis and treatment of viral hepatitis and its associated liver diseases. Several studies have reported that viral hepatitis and its associated liver diseases, including hepatitis A, B, C and E; hepatic fibrosis and hepatocellular carcinoma, were closely associated with exosomes. Exploring the role of exosomes in viral hepatitis and associated liver diseases will enhance our understanding of these diseases. Therefore, this review mainly summarised the role of exosomes in viral hepatitis and its associated liver diseases to identify new strategies for liver diseases in clinical practise.

Cell Division Control Protein 42 Interacts With Hepatitis E Virus Capsid Protein and Participates in Hepatitis E Virus Infection

Hepatitis E Virus (HEV) causes viral hepatitis in humans worldwide, while a subset of HEV species, avian HEV, causes hepatitis-splenomegaly syndrome in chickens. To date, there are few reports on the host proteins interacting with HEV and being involved in viral infection. Previous pull-down assay combining mass spectrometry indicated that cell division control protein 42 (CDC42), a member belonging to the Rho GTPase family, was pulled down by avian HEV capsid protein. We confirmed the direct interaction between CDC42 and avian and mammalian HEV capsid proteins. The interaction can increase the amount of active guanosine triphosphate binding CDC42 state (GTP-CDC42). Subsequently, we determined that the expression and activity of CDC42 were positively correlated with HEV infection in the host cells. Using the different inhibitors of CDC42 downstream signaling pathways, we found that CDC42-MRCK (a CDC42-binding kinase)-non-myosin IIA (NMIIA) pathway is involved in naked avian and mammalian HEV infection, CDC42-associated p21-activated kinase 1 (PAK1)-NMIIA/Cofilin pathway is involved in quasi-enveloped mammalian HEV infection and CDC42-neural Wiskott-Aldrich syndrome protein-actin-polymerizing protein Arp2/3 pathway (CDC42-(N-)WASP-Arp2/3) pathway participates in naked and quasi-enveloped mammalian HEV infection. Collectively, these results demonstrated for the first time that HEV capsid protein can directly bind to CDC42, and non- and quasi-enveloped HEV use different CDC42 downstream signaling pathways to participate in viral infection. The study provided some new insights to understand the life cycle of HEV in host cells and a new target of drug design for combating HEV infection.

The Viral ORF3 Protein Is Required for Hepatitis E Virus Apical Release and Efficient Growth in Polarized Hepatocytes and Humanized Mice

Hepatitis E virus (HEV), an enterically transmitted RNA virus, is a major cause of acute hepatitis worldwide. Additionally, HEV genotype 3 (gt3) can frequently persist in immunocompromised individuals with an increased risk for developing severe liver disease. Currently, no HEV-specific treatment is available. The viral open reading frame 3 (ORF3) protein facilitates HEV egress in vitro and is essential for establishing productive infection in macaques. Thus, ORF3, which is unique to HEV, has the potential to be explored as a target for antiviral therapy. However, significant gaps exist in our understanding of the critical functions of ORF3 in HEV infection in vivo. Here, we utilized a polarized hepatocyte culture model and a human liver chimeric mouse model to dissect the roles of ORF3 in gt3 HEV release and persistent infection. We show that ORF3's absence substantially decreased HEV replication and virion release from the apical surface but not the basolateral surface of polarized hepatocytes. While wild-type HEV established a persistent infection in humanized mice, mutant HEV lacking ORF3 (ORF3null) failed to sustain the infection despite transient replication in the liver and was ultimately cleared. Strikingly, mice inoculated with the ORF3null virus displayed no fecal shedding throughout the 6-week experiment. Overall, our results demonstrate that ORF3 is required for HEV fecal shedding and persistent infection, providing a rationale for targeting ORF3 as a treatment strategy for HEV infection. IMPORTANCE HEV infections are associated with significant morbidity and mortality. HEV gt3 additionally can cause persistent infection, which can rapidly progress to liver cirrhosis. Currently, no HEV-specific treatments are available. The poorly understood HEV life cycle hampers the development of antivirals for HEV. Here, we investigated the role of the viral ORF3 protein in HEV infection in polarized hepatocyte cultures and human liver chimeric mice. We found that two major aspects of the HEV life cycle require ORF3: fecal virus shedding and persistent infection. These results provide a rationale for targeting ORF3 to treat HEV infection.

The Hepatitis E Virus Open Reading Frame 2 Protein: Beyond Viral Capsid

Hepatitis E virus (HEV) is a zoonotic pathogen causing hepatitis in both human and animal hosts, which is responsible for acute hepatitis E outbreaks worldwide. The 7.2 kb genome of the HEV encodes three well-defined open reading frames (ORFs), where the ORF2 translation product acts as the major virion component to form the viral capsid. In recent years, besides forming the capsid, more functions have been revealed for the HEV-ORF2 protein, and it appears that HEV-ORF2 plays multiple functions in both viral replication and pathogenesis. In this review, we systematically summarize the recent research advances regarding the function of the HEV-ORF2 protein such as application in the development of a vaccine, regulation of the innate immune response and cellular signaling, involvement in host tropism and participation in HEV pathogenesis as a novel secretory factor. Progress in understanding more of the function of HEV-ORF2 protein beyond the capsid protein would contribute to improved control and treatment of HEV infection.

Cellular Organelles Involved in Hepatitis E Virus Infection

Hepatitis E virus (HEV), a major cause of acute hepatitis worldwide, infects approximately 20 million individuals annually. HEV can infect a wide range of mammalian and avian species, and cause frequent zoonotic spillover, increasingly raising public health concerns. To establish a successful infection, HEV needs to usurp host machineries to accomplish its life cycle from initial attachment to egress. However, relatively little is known about the HEV life cycle, especially the functional role(s) of cellular organelles and their associated proteins at different stages of HEV infection. Here, we summarize current knowledge regarding the relation of HEV with the different cell organelles during HEV infection. Furthermore, we discuss the underlying mechanisms by which HEV infection is precisely regulated in infected cells and the modification of host cell organelles and their associated proteins upon HEV infection.

Hepatitis E Virus Immunopathogenesis

Hepatitis E virus is an important emerging pathogen producing a lethal impact on the pregnant population and immunocompromised patients. Starting in 1983, it has been described as the cause for acute hepatitis transmitted via the fecal–oral route. However, zoonotic and blood transfusion transmission of HEV have been reported in the past few decades, leading to the detailed research of HEV pathogenesis. The reason behind HEV being highly virulent to the pregnant population particularly during the third trimester, leading to maternal and fetal death, remains unknown. Various host factors (immunological, nutritional, hormonal) and viral factors have been studied to define the key determinants assisting HEV to be virulent in pregnant and immunocompromised patients. Similarly, chronic hepatitis is seen particularly in solid organ transplant patients, resulting in fatal conditions. This review describes recent advances in the immunopathophysiology of HEV infections in general, pregnant, and immunocompromised populations, and further elucidates the in vitro and in vivo models utilized to understand HEV pathogenesis.

Resolution of hepatitis E virus infection in CD8+ T cell-depleted rhesus macaques

BACKGROUND & AIMS

HEV is a significant cause of acute hepatitis globally. Some genotypes establish persistent infection when immunity is impaired. Adaptive immune mechanisms that mediate resolution of infection have not been identified. Herein, the requirement for CD8+ T cells to control HEV infection was assessed in rhesus macaques, a model of acute and persistent HEV infection in humans.

METHODS

Rhesus macaques were untreated or treated with depleting anti-CD8α monoclonal antibodies before challenge with an HEV genotype (gt)3 isolate derived from a chronically infected human patient. HEV replication, alanine aminotransferase, anti-capsid antibody and HEV-specific CD4+ and CD8+ T cell responses were assessed after infection.

RESULTS

HEV control in untreated macaques coincided with the onset of a neutralizing IgG response against the ORF2 capsid and liver infiltration of functional HEV-specific CD4+ and CD8+ T cells. Virus control was delayed by 1 week in CD8+ T cell-depleted macaques. Infection resolved with onset of a neutralizing IgG antibody response and a much more robust expansion of CD4+ T cells with antiviral effector function.

CONCLUSIONS

Liver infiltration of functional CD8+ T cells coincident with HEV clearance in untreated rhesus macaques, and a 1-week delay in HEV clearance in CD8+ T cell-depleted rhesus macaques, support a role for this subset in timely control of virus replication. Resolution of infection in the absence of CD8+ T cells nonetheless indicates that neutralizing antibodies and/or CD4+ T cells may act autonomously to inhibit HEV replication. HEV susceptibility to multiple adaptive effector mechanisms may explain why persistence occurs only with generalized immune suppression. The findings also suggest that neutralizing antibodies and/or CD4+ T cells should be considered as a component of immunotherapy for chronic infection.

LAY SUMMARY

The hepatitis E virus (HEV) is a major cause of liver disease globally. Some genetic types (genotypes) of HEV persist in the body if immunity is impaired. Our objective was to identify immune responses that promote clearance of HEV. Findings indicate that HEV may be susceptible to multiple arms of the immune response that can act independently to terminate infection. They also provide a pathway to assess immune therapies for chronic HEV infection.

Phenotypic characterization of cell culture-derived hepatitis E virus subjected to different chemical treatments: Application in virus removal via nanofiltration

Safety evaluation for the hepatitis E virus (HEV) is required for plasma fractionation products. Plasma-derived HEV (pHEV) is quite unique in that it is associated with a lipid membrane, which, when stripped during manufacturing processes, induces morphological changes in the virus, making it difficult to select proper HEV phenotypes for clearance studies. We developed a convenient system for the preparation of a high titer cell culture-derived HEV (cHEV). In this system, PLC/PRF/5 cells transfected with the wild-type HEV genome generated lipid membrane-associated cHEV for a long period even after cryopreservation. We also examined how this lipid membrane-associated cHEV can be used to verify the robustness of pHEV removal via 19-nm nanofiltration. Sodium-deoxycholate and trypsin (NaDOC/T) treatment not only dissolved lipid but also digested membrane-associated proteins from pHEV and cHEV, making the resulting cHEV particle smaller in size than any pHEV phenotypes generated by ethanol or solvent-detergent treatment in this study. In both 19-nm and 35-nm nanofiltration, cHEV behaved identically to pHEV. These results indicate that cHEV is a useful resource for viral clearance studies in term of availability, and the use of NaDOC/T-treated cHEV ensured robust pHEV removal capacity via 19-nm nanofiltration.

A New Infectious Unit: Extracellular Vesicles Carrying Virus Populations

Viral egress and transmission have long been described to take place through single free virus particles. However, viruses can also shed into the environment and transmit as populations clustered inside extracellular vesicles (EVs), a process we had first called vesicle-mediated en bloc transmission. These membrane-cloaked virus clusters can originate from a variety of cellular organelles including autophagosomes, plasma membrane, and multivesicular bodies. Their viral cargo can be multiples of nonenveloped or enveloped virus particles or even naked infectious genomes, but egress is always nonlytic, with the cell remaining intact. Here we put forth the thesis that EV-cloaked viral clusters are a distinct form of infectious unit as compared to free single viruses (nonenveloped or enveloped) or even free virus aggregates. We discuss how efficient and prevalent these infectious EVs are in the context of virus-associated diseases and highlight the importance of their proper detection and disinfection for public health. Expected final online publication date for the Annual Review of Cell and Developmental Biology, Volume 37 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Hepatitis E virus egress and beyond - the manifold roles of the viral ORF3 protein

Although the hepatitis E virus represents an uprising threat to the global community by representing the commonest cause of an acute viral hepatitis worldwide, its life cycle is grossly understudied. Albeit HEV is a non-enveloped virus, its progeny is released as quasi-enveloped virions. Thus, the responsible accessory protein pORF3 gained rising attention in the past years. It mediates viral release via the exosomal route by targeting the viral capsid to the endosomal system, more precisely to multivesicular bodies. As this is followed by quasi-envelopment, pORF3 may in terms represent a substitute to a conventional envelope protein. This feature proofs to be rather unique with respect to other enteric viruses, although the protein's role in the viral life cycle seems to reach far beyond simply maintaining release of progeny viruses. How pORF3 affects viral morphogenesis, how it mediates efficient viral release and how it supports viral spread is summarised in this microreview. With this, we aim to shed light on functions of pORF3 to gain further insights in still enigmatic aspects of the HEV life cycle. TAKE AWAYS: HEV is released as exosome via multivesicular bodies Viral pORF3 mediates release via endosomal complexes required for transport pORF3 modulates various cellular processes in infected cells Elucidation of pORF3-related processes imply novel clinical strategies.

The different replication between nonenveloped and quasi-enveloped hepatitis E virus

Hepatitis E virus (HEV) is the major pathogen of viral hepatitis. However, the understanding of the HEV life cycle is limited. In the present study, cells were separately infected with nonenveloped HEV (derived from feces or bile) or quasi-enveloped HEV (derived from the cell culture after serial passages, eHEV) and observed by confocal fluorescence microscopy to investigate the life cycle of HEV. HEV finished its binding and entry into host cells at first 6 h postinoculation (hpi). Cells inoculated with eHEV showed less infectivity than cells inoculated with nonenveloped HEV. Newly synthesized progeny virions were released into the supernatant of cell cultures from 48 hpi. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analysis results showed that the supernatant's progeny viruses were infectious even after five serial passages. These results show the significant difference between nonenveloped HEV and eHEV, which will provide novel insights into the HEV replication cycle. The efficient cell culture of HEV will promote the development of anti-HEV drugs and vaccines.

Open reading frame 3 protein of hepatitis E virus: Multi-function protein with endless potential

Hepatitis E virus (HEV), a fecal-orally transmitted foodborne viral pathogen, causes acute hepatitis in humans and is responsible for hepatitis E outbreaks worldwide. Since the identification of HEV as a zoonotic agent, this virus has been isolated from a variety of hosts with an ever-expanding host range. HEV-open reading frame (ORF) 3, the smallest ORF in HEV genomes, initially had been perceived as an unremarkable HEV accessory protein. However, as novel HEV-ORF3 function has been discovered that is related to the existence of a putative third virion structural form, referred to as “quasi-enveloped” HEV particles, HEV is challenging the conventional virion structure-based classification scheme, which assigns all viruses to two groups, “enveloped” or “non-enveloped”. In this review, we systematically describe recent progress that has identified multiple pathogenic roles of HEV-ORF3, including roles in HEV virion release, biogenesis of quasi-enveloped virus, regulation of the host innate immune response, and interference with host signaling pathways. In addition, implications of HEV-ORF3-associated quasi-enveloped virions are discussed to guide future development of improved vaccines against zoonotic HEV infection.

NPC1-regulated dynamic of clathrin-coated pits is essential for viral entry

Viruses utilize cellular lipids and manipulate host lipid metabolism to ensure their replication and spread. Therefore, the identification of lipids and metabolic pathways that are suitable targets for antiviral development is crucial. Using a library of compounds targeting host lipid metabolic factors and testing them for their ability to block pseudorabies virus (PRV) and vesicular stomatitis virus (VSV) infection, we found that U18666A, a specific inhibitor of Niemann-Pick C1 (NPC1), is highly potent in suppressing the entry of diverse viruses including pseudotyped severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). NPC1 deficiency markedly attenuates viral growth by decreasing cholesterol abundance in the plasma membrane, thereby inhibiting the dynamics of clathrin-coated pits (CCPs), which are indispensable for clathrin-mediated endocytosis. Significantly, exogenous cholesterol can complement the dynamics of CCPs, leading to efficient viral entry and infectivity. Administration of U18666A improves the survival and pathology of PRV- and influenza A virus-infected mice. Thus, our studies demonstrate a unique mechanism by which NPC1 inhibition achieves broad antiviral activity, indicating a potential new therapeutic strategy against SARS-CoV-2, as well as other emerging viruses.

Mechanism of Cross-Species Transmission, Adaptive Evolution and Pathogenesis of Hepatitis E Virus

Hepatitis E virus (HEV) is the leading cause of acute hepatitis worldwide. While the transmission in developing countries is dominated by fecal-oral route via drinking contaminated water, the zoonotic transmission is the major route of HEV infection in industrialized countries. The discovery of new HEV strains in a growing number of animal species poses a risk to zoonotic infection. However, the exact mechanism and the determinant factors of zoonotic infection are not completely understood. This review will discuss the current knowledge on the mechanism of cross-species transmission of HEV infection, including viral determinants, such as the open reading frames (ORFs), codon usage and adaptive evolution, as well as host determinants, such as host cellular factors and the host immune status, which possibly play pivotal roles during this event. The pathogenesis of hepatitis E infection will be briefly discussed, including the special forms of this disease, including extrahepatic manifestations, chronic infection, and fulminant hepatitis in pregnant women.

Strategy, Progress, and Challenges of Drug Repurposing for Efficient Antiviral Discovery

Emerging or re-emerging viruses are still major threats to public health. Prophylactic vaccines represent the most effective way to prevent virus infection; however, antivirals are more promising for those viruses against which vaccines are not effective enough or contemporarily unavailable. Because of the slow pace of novel antiviral discovery, the high disuse rates, and the substantial cost, repurposing of the well-characterized therapeutics, either approved or under investigation, is becoming an attractive strategy to identify the new directions to treat virus infections. In this review, we described recent progress in identifying broad-spectrum antivirals through drug repurposing. We defined the two major categories of the repurposed antivirals, direct-acting repurposed antivirals (DARA) and host-targeting repurposed antivirals (HTRA). Under each category, we summarized repurposed antivirals with potential broad-spectrum activity against a variety of viruses and discussed the possible mechanisms of action. Finally, we proposed the potential investigative directions of drug repurposing.

Structural and molecular biology of hepatitis E virus

Hepatitis E virus (HEV) is one of the most common causes of acute viral hepatitis, mainly transmitted by fecal-oral route but has also been linked to fulminant hepatic failure, chronic hepatitis, and extrahepatic neurological and renal diseases. HEV is an emerging zoonotic pathogen with a broad host range, and strains of HEV from numerous animal species are known to cross species barriers and infect humans. HEV is a single-stranded, positive-sense RNA virus in the family Hepeviridae. The genome typically contains three open reading frames (ORFs): ORF1 encodes a nonstructural polyprotein for virus replication and transcription, ORF2 encodes the capsid protein that elicits neutralizing antibodies, and ORF3, which partially overlaps ORF2, encodes a multifunctional protein involved in virion morphogenesis and pathogenesis. HEV virions are non-enveloped spherical particles in feces but exist as quasi-enveloped particles in circulating blood. Two types of HEV virus-like particles (VLPs), small T = 1 (270 Å) and native virion-sized T = 3 (320-340 Å) have been reported. There exist two distinct forms of capsid protein, the secreted form (ORF2S) inhibits antibody neutralization, whereas the capsid-associated form (ORF2C) self-assembles to VLPs. Four cis-reactive elements (CREs) containing stem-loops from secondary RNA structures have been identified in the non-coding regions and are critical for virus replication. This mini-review discusses the current knowledge and gaps regarding the structural and molecular biology of HEV with emphasis on the virion structure, genomic organization, secondary RNA structures, viral proteins and their functions, and life cycle of HEV.

Emerging role and therapeutic application of exosome in hepatitis virus infection and associated diseases

Hepatitis viruses are chief pathogens of hepatitis and end-stage liver diseases. Their replication and related pathogenic process highly rely on the host micro-environment and multiple cellular elements, including exosomes. Representing with a sort of cell-derived vesicle structure, exosomes were considered to be dispensable cellular components, even wastes. Along with advancing investigation, a specific profile of exosome in driving hepatitis viruses' infection and hepatic disease progression is revealed. Exosomes greatly affect the pathogenesis of hepatitis viruses by mediating their replication and modulating the host immune responses. The characteristics of host exosomes are markedly changed after infection with hepatitis viruses. Exosomes released from hepatitis virus-infected cells can carry viral nucleic or protein components, thereby acting as an effective subterfuge for hepatitis viruses by participating in viral transportation and immune escape. On the contrary, immune cell-derived exosomes contribute toward the innate antiviral immune defense and virus eradication. There is growing evidence supporting the application of exosomal biomarkers for predicting disease progress or therapeutic outcome, while exosomal nanoshuttles are regarded as promising therapeutic options based on their delivery properties and immune compatibility. In this review, we summarize the biogenesis and secretion mechanism of exosomes, review the recent findings pertaining to the role of exosomes in the interplay between hepatitis viruses and innate immune responses, and conclude their potential in further therapeutic application.

Egress of non-enveloped enteric RNA viruses

A long-standing paradigm in virology was that non-enveloped viruses induce cell lysis to release progeny virions. However, emerging evidence indicates that some non-enveloped viruses exit cells without inducing cell lysis, while others engage both lytic and non-lytic egress mechanisms. Enteric viruses are transmitted via the faecal-oral route and are important causes of a wide range of human infections, both gastrointestinal and extra-intestinal. Virus cellular egress, when fully understood, may be a relevant target for antiviral therapies, which could minimize the public health impact of these infections. In this review, we outline lytic and non-lytic cell egress mechanisms of non-enveloped enteric RNA viruses belonging to five families: Picornaviridae, Reoviridae, Caliciviridae, Astroviridae and Hepeviridae. We discuss factors that contribute to egress mechanisms and the relevance of these mechanisms to virion stability, infectivity and transmission. Since most data were obtained in traditional two-dimensional cell cultures, we will further attempt to place them into the context of polarized cultures and in vivo pathogenesis. Throughout the review, we highlight numerous knowledge gaps to stimulate future research into the egress mechanisms of these highly prevalent but largely understudied viruses.

Hepatitis E virus: Efficacy of pasteurization of plasma-derived VWF/FVIII concentrate determined by pig bioassay

BACKGROUND

Hepatitis E virus (HEV) is the leading cause of acute hepatitis throughout the world. Increasing blood component transfusion-associated HEV infections highlight the need for reliable virus inactivation procedures for plasma derivatives from pooled plasma donations.

STUDY DESIGN AND METHODS

An animal infection study was conducted to evaluate the efficiency of HEV inactivation by pasteurization during the manufacturing process of the von Willebrand Factor/Factor VIII (VWF/FVIII) concentrate Haemate P/Humate-P (CSL Behring, Marburg, Germany). For this purpose, groups of pigs were inoculated with stabilized VWF/FVIII intermediate spiked with HEV-positive liver homogenate and exposed to increasing incubation times of 0, 3, 6, and 10 h at 60°C. Animals were evaluated for virus replication over 27 days and in a subsequent trial over 92 days.

RESULTS

Virus replication was detected in animals up to the 6-h pasteurization group. In contrast, pasteurization for 10 h did not reveal virus detection when the observation period was 27 days. In an additional experiment using the 10-h pasteurized material, two individuals started virus excretion and seroconverted when the observation period was extended to 92 days. Based on the total infection rate (2 of 12) of the animals inoculated with the sample pasteurized for 10 h, a virus reduction factor of at least 4.7 log₁₀ is calculated.

CONCLUSION

This study demonstrates that pasteurization at 60°C for 10 h of an HEV-positive plasma derivative leads to the effective reduction of infectivity, resulting in a VWF/FVIII product with an appropriate margin of safety for HEV.

Advances in Hepatitis E Virus Biology and Pathogenesis

Hepatitis E virus (HEV) is one of the causative agents for liver inflammation across the world. HEV is a positive-sense single-stranded RNA virus. Human HEV strains mainly belong to four major genotypes in the genus Orthohepevirus A, family Hepeviridae. Among the four genotypes, genotype 1 and 2 are obligate human pathogens, and genotype 3 and 4 cause zoonotic infections. HEV infection with genotype 1 and 2 mainly presents as acute and self-limiting hepatitis in young adults. However, HEV infection of pregnant women with genotype 1 strains can be exacerbated to fulminant hepatitis, resulting in a high rate of case fatality. As pregnant women maintain the balance of maternal-fetal tolerance and effective immunity against invading pathogens, HEV infection with genotype 1 might dysregulate the balance and cause the adverse outcome. Furthermore, HEV infection with genotype 3 can be chronic in immunocompromised patients, with rapid progression, which has been a challenge since it was reported years ago. The virus has a complex interaction with the host cells in downregulating antiviral factors and recruiting elements to generate a conducive environment of replication. The virus-cell interactions at an early stage might determine the consequence of the infection. In this review, advances in HEV virology, viral life cycle, viral interference with the immune response, and the pathogenesis in pregnant women are discussed, and perspectives on these aspects are presented.

Immunogenicity of gold nanoparticle-based truncated ORF2 vaccine in mice against Hepatitis E virus

This study presents nanoparticle-based vaccine development for Hepatitis E virus (HEV). Gold nanoparticles (GNP) of average size 12 nm were synthesized by citrate reduction method followed by functionalization with cysteamine hydrochloride for nano-conjugation. Immune response of nano-conjugates of GNP with 26 kDa protein (368-606 amino acids) and 54 kDa protein (112-606 amino acids) were evaluated. In vitro release kinetics of GNP-conjugated 54 kDa (GNP54) and 26 kDa (GNP26) proteins showed slower rate of release of 54 kDa protein as compared to 26 kDa protein. Humoral immune response of mice immunized intramuscularly with GNP54, GNP26 and GNP alone, exhibited HEV-specific IgG titer of 7.9 ± 2.9, 5.686 ± 4.098 and 0.698 ± 0.089, respectively, after 14 days of booster immunization. In addition to this, HEV-specific cell-mediated immune response was demonstrated by splenocyte proliferation assay. Analysis of results using one-way ANOVA, showed statistically significant (p value < 0.05) increase in splenocyte proliferation for GNP54- and GNP26-immunized mice in comparison to GNP alone immunized mice. Stimulation index of HEV ORF2 proteins in GNP54/GNP26-immunized mice were comparable to Concanavalin A-treated positive control. These results indicate GNP-based vaccine as a promising candidate for efficiently mediating both humoral and cell-mediated immune response against HEV.

Current Paradigm of Hepatitis E Virus Among Pediatric and Adult Patients

Hepatitis E virus (HEV) infection is a polymorphic condition, present throughout the world and involving children and adults. Multiple studies over the last decade have contributed to a better understanding of the natural evolution of this infection in various population groups, several reservoirs and transmission routes being identified. To date, acute or chronic HEV-induced hepatitis has in some cases remained underdiagnosed due to the lower accuracy of serological tests and due to the evolutionary possibility with extrahepatic manifestations. Implementation of diagnostic tests based on nucleic acid analysis has increased the detection rate of this disease. The epidemiological and clinical features of HEV hepatitis differ depending on the geographical areas studied. HEV infection is usually a self-limiting condition in immunocompetent patients, but in certain categories of vulnerable patients it can induce a sudden evolution toward acute liver failure (pregnant women) or chronicity (immunosuppressed patients, post-transplant, hematological, or malignant diseases). In acute HEV infections in most cases supportive treatment is sufficient. In patients who develop chronic hepatitis with HEV, dose reduction of immunosuppressive medication should be the first therapeutic step, especially in patients with transplant. In case of unfavorable response, the initiation of antiviral therapy is recommended. In this review, the authors summarized the essential published data related to the epidemiological, clinical, paraclinical, and therapeutic aspects of HEV infection in adult and pediatric patients.

Stability of hepatitis E virus at high hydrostatic pressure processing

Hepatitis E virus (HEV) is the causative agent of acute and chronic hepatitis in humans. The zoonotic HEV genotype 3 is the main genotype in Europe. The foodborne transmission via consumption of meat and meat products prepared from infected pigs or wild boars is considered the major transmission route of this genotype. High hydrostatic pressure processing (HPP) is a technique, which can be used for inactivation of pathogens in food. Here, preparations of a cell culture-adapted HEV genotype 3 strain in phosphate-buffered saline (PBS) were subjected to HPP and the remaining infectivity was titrated in cell culture by counting fluorescent foci of replicating virus. A gradual decrease in infectivity was found by application of 100 to 600 MPa for 2 min. At 20 °C, infectivity reduction of 0.5 log₁₀ at 200 MPa and 1 log₁₀ at 400 MPa were observed. Slightly higher infectivity reduction of 1 log₁₀ at 200 MPa and 2 log₁₀ at 400 MPa were found by application of the pressure at 4 °C. At both temperatures, the virus was nearly completely inactivated (>3.5 log₁₀ infectivity decrease) at 600 MPa; however, low amounts of remaining infectious virus were observed in one of three replicates in both cases. Transmission electron microscopy showed disassembled and distorted particles in the preparations treated with 600 MPa. Time-course experiments at 400 MPa showed a continuous decline of infectivity from 30 s to 10 min, leading to a 2 log₁₀ infectivity decrease at 20 °C and to a 2.5 log₁₀ infectivity decrease at 4 °C for a 10 min pressure application each. Predictive models for inactivation of HEV by HPP were generated on the basis of the generated data. The results show that HPP treatment can reduce HEV infectivity, which is mainly dependent on pressure height and duration of the HPP treatment. Compared to other viruses, HEV appears to be relatively stable against HPP and high pressure/long time combinations have to be applied for significant reduction of infectivity.

Stable Expression of a Hepatitis E Virus (HEV) RNA Replicon in Two Mammalian Cell Lines to Assess Mechanism of Innate Immunity and Antiviral Response

Hepatitis E virus (HEV) is one of the major etiological agents responsible for acute hepatitis. Hepatitis E virus does not replicate efficiently in mammalian cell cultures, thus a useful model that mimics persistent HEV replication is needed to dissect the molecular mechanism of pathogenesis. Here we report a genotype-3 HEV RNA replicon expressing an EGFP-Zeocin (EZ) resistant gene (p6-EZ) that persistently self-replicated in cell lines of human (Huh-7-S10-3) or hamster (BHK-21) origin after transfection with in vitro RNA transcripts and subsequent drug screening. Two cell lines, S10-3-EZ and BHK-21-EZ, stably expressed EGFP in the presence of Zeocin during continuous passages. Both genomic and subgenomic HEV RNAs and viral replicase proteins were stably expressed in persistent HEV replicon cells. The values of the cell models in antiviral testing, innate immune RNA sensing and type I IFN in host defense were further demonstrated. We revealed a role of RIG-I like receptor-interferon regulatory factor 3 in host antiviral innate immune sensing during HEV replication. We further demonstrated that treatment with interferon (IFN-α) or ribavirin significantly reduced expression of replicon RNA in a dose-dependent manner. The availability of the models will greatly facilitate HEV-specific antiviral development, and delineate mechanisms of HEV replication.

Effect of Sodium Chloride, Sodium Nitrite and Sodium Nitrate on the Infectivity of Hepatitis E Virus

Hepatitis E virus (HEV) infection can cause acute and chronic hepatitis in humans. The zoonotic HEV genotype 3, which is highly prevalent in Europe, is mainly transmitted by consumption of raw meat and raw meat products produced from infected pigs or wild boars. High salt concentrations represent an important measure to preserve meat products and to inactivate foodborne pathogens. Here, an HEV preparation in phosphate-buffered saline (PBS) was subjected to different salt concentrations and the remaining infectivity was measured in a cell culture assay. Treatments with up to 20% sodium chloride for 24 h at 23 °C, with and without addition of 0.015% sodium nitrite or 0.03% sodium nitrate, did not lead to virus inactivation as compared to PBS only. Conditions usually applied for short-term and long-term fermented raw sausages were simulated by incubation at 22 °C for up to 6 days and at 16 °C for up to 8 weeks, respectively. Only 2% sodium chloride with 0.015% sodium nitrite showed a weak (< 1 log₁₀), but significant, infectivity reduction after 2 and 4 days as compared to PBS only. Addition of 2% sodium chloride and 0.03% sodium nitrate showed a slight, but not significant, decrease in infectivity after 2 and 8 weeks as compared to PBS only. In conclusion, HEV is highly stable at high salt concentrations and at salt conditions usually applied to preserve raw meat products.

Full-length genome sequencing of RNA viruses-How the approach can enlighten us on hepatitis C and hepatitis E viruses

Among the five main viruses responsible for human hepatitis, hepatitis C virus (HCV) and hepatitis E virus (HEV) are different while sharing similarities. Both viruses can be transmitted by blood or derivatives whereas HEV can also follow environmental or zoonotic routes. These highly variable RNA viruses can cause chronic hepatitis potentially leading to hepatocarcinoma. HCV and HEV can develop new structures and functions under selective pressure to adapt to host immunity, human tissues, treatments or even various animal reservoirs. Elsewhere, with directly acting antiviral treatments, HCV can be eradicated whereas HEV is an emerging pathogen against which specific treatments have to be improved. As a unique molecular tool able to explore viral genomic plasticity, full-length genome (FLG) sequencing has become easier, faster and cheaper. The present review will show how FLG sequencing can explore these RNA viruses with the aim to investigate key genomics data to improve basic knowledge, patients' healthcare and preventive tools.

Virus spread in the liver: mechanisms, commonalities, and unanswered questions

The liver is home to five known human hepatitis viruses (hepatitis A virus-hepatitis E virus). Despite being phylogenetically unrelated, these viruses replicate and spread in the liver without causing apparent cytopathic effects, and all have evolved strategies to counteract antibody-mediated inhibition of virus spread. In this review, we discuss the current understanding regarding the spread mechanisms for these viruses with an attempt to extract common principles and identify key questions for future studies.

Hepatitis E Virus Infection: Circulation, Molecular Epidemiology, and Impact on Global Health

Infection with hepatitis E virus (HEV) represents the most common source of viral hepatitis globally. Although infecting over 20 million people annually in endemic regions, with major outbreaks described since the 1950s, hepatitis E remains an underestimated disease. This review gives a current view of the global circulation and epidemiology of this emerging virus. The history of HEV, from the first reported enteric non-A non-B hepatitis outbreaks, to the discovery of the viral agent and the molecular characterization of the different human pathogenic genotypes, is discussed. Furthermore, the current state of research regarding the virology of HEV is critically assessed, and the challenges towards prevention and diagnosis, as well as clinical risks of the disease described. Together, these points aim to underline the significant impact of hepatitis E on global health and the need for further in-depth research to better understand the pathophysiology and its role in the complex disease manifestations of HEV infection.

Quasi-enveloped hepatitis virus assembly and release

Hepatitis A virus (HAV) and hepatitis E virus (HEV) infections are the main causes for acute hepatitis worldwide. Both viruses had long been considered as nonenveloped viruses. However, recent work has uncovered that both viruses circulate in the bloodstream as membrane-cloaked, "quasi-enveloped" particles that are, surprisingly, infectious and likely the only form mediating virus spread within the host. The discovery of quasi-enveloped HAV and HEV particles has fundamentally changed the traditional view on the life cycle and pathogenesis of these viruses. However, because HAV and HEV are phylogenetically unrelated and their capsid assembly processes are quite distinct, it is not clear whether they use similar or different mechanisms for envelopment and exit. This review provides an overview of the current knowledge about the assembly and exit processes of HAV and HEV and perspectives for future studies.