Hepatitis E Virus Genome Structure and Replication Strategy

A novel multi-epitope peptide vaccine candidate targeting hepatitis E virus: An in silico approach

Hepatitis E virus (HEV) is a foodborne virus transmitted through the faecal-oral route that causes viral hepatitis in humans worldwide. Ever since its discovery as a zoonotic agent, HEV was isolated from several species with an expanding range of hosts. HEV possesses several features of other RNA viruses but also has certain HEV-specific traits that make its viral-host interactions inimitable. HEV leads to severe morbidity and mortality in immunocompromised people and pregnant women across the world. The situation in underdeveloped countries is even more alarming. Even after creating a menace across the world, we still lack an effective vaccine against HEV. Till date, there is only one licensed vaccine for HEV available only in China. The development of an anti-HEV vaccine that can reduce HEV-induced morbidity and mortality is required. Live attenuated and killed vaccines against HEV are not accessible due to the lack of a tolerant cell culture system, slow viral replication kinetics and varying growth conditions. Thus, the main focus for anti-HEV vaccine development is now on the molecular approaches. In the current study, we have designed a multi-epitope vaccine against HEV through a reverse vaccinology approach. For the first time, we have used viral ORF3, capsid protein and polyprotein altogether for epitope prediction. These are crucial for viral replication and persistence and are major vaccine targets against HEV. The proposed in silico vaccine construct comprises of highly immunogenic and antigenic T-cell and B-cell epitopes of HEV proteins. The construct is capable of inducing an effective and long-lasting host immune response as evident from the simulation results. In addition, the construct is stable, non-allergic and antigenic for the host. Altogether, our findings suggest that the in silico vaccine construct may be useful as a vaccine candidate for preventing HEV infections.

Recent decline in hepatitis E virus prevalence among wild boars in Japan: Probably due to countermeasures implemented in response to outbreaks of classical swine fever virus infection

Previous studies have emphasized the necessity of surveillance and control measures for hepatitis E virus (HEV) infection in wild boars, an important reservoir of HEV. To assess the current situation of HEV infection in wild boars in Japan, this study investigated the prevalence and genetic diversity of HEV among wild boars captured in 16 prefectures of Japan during 2018-2023. Serum samples from 968 wild boars were examined for anti-HEV IgG antibodies and HEV RNA. The prevalence of anti-HEV IgG varied geographically from 0 % to 35.0 %. HEV RNA was detected in 3.6 % of boars, with prevalence varying by prefecture from 0 % to 22.2 %. Genotype 3 was the most prevalent genotype (91.9 %), followed by genotype 4 (5.4 %), with one strain closely related to genotype 6. The prevalence of HEV infection among wild boars decreased from 2018/2019 to 2022/2023 with significant declines in levels of anti-HEV IgG antibodies (14.5 % vs. 6.2 %, P < 0.0001) and HEV RNA (7.6 % vs. 1.5 %, P < 0.0001). Regional analysis showed varying trends, with no HEV RNA-positive boars found in several regions in recent years. A plausible factor contributing to the decline in HEV infection is the application of countermeasures, including installing fences to prevent intrusion into pig farms, implemented in response to the emergence of classical swine fever virus (CSFV) infection in wild boars and domestic pigs, with incidents reported annually since 2018. Further investigation is warranted to explore the association between countermeasures to CSFV infection and the decrease in HEV infection among wild boars.

Recent advances in hepatitis E virus research and the Japanese clinical practice guidelines for hepatitis E virus infection

Acute hepatitis E was considered rare until reports emerged affirming the existence of hepatitis E virus (HEV) genotypes 3 and 4 infections in Japan in the early 2000s. Extensive studies by Japanese researchers have highlighted the pivotal role of pigs and wild animals, such as wild boars and deer, as reservoirs for HEV, linking them to zoonotic infections in Japan. Currently, when hepatitis occurs subsequent to the consumption of undercooked or grilled pork, wild boar meat, or offal (including pig liver and intestines), HEV infection should be considered. Following the approval of anti-HEV immunoglobulin A antibody as a diagnostic tool for hepatitis E by Japan's Health Insurance System in 2011, the annual number of diagnosed cases of HEV infection has surged. Notably, the occurrence of post-transfusion hepatitis E promoted nationwide screening of blood products for HEV using nucleic acid amplification tests since 2020. Furthermore, chronic hepatitis E has been observed in immunosuppressed individuals. Considering the significance of hepatitis E, heightened preventive measures are essential. The Japan Agency for Medical Research and Development Hepatitis A and E viruses (HAV and HEV) Study Group, which includes special virologists and hepatologists, held a virtual meeting on February 17, 2024. Discussions encompassed pathogenesis, transmission routes, diagnosis, complications, severity factors, and ongoing and prospective vaccination or treatments for hepatitis E. Rigorous assessment of referenced studies culminated in the formulation of recommendations, which are detailed within this review. This comprehensive review presents recent advancements in HEV research and Japanese clinical practice guidelines for HEV infection.

Characterization of virus‒host recombinant variants of the hepatitis E virus

Hepatitis E virus is a single-strand, positive-sense RNA virus that can lead to chronic infection in immunocompromised patients. Virus-host recombinant variants (VHRVs) have been described in such patients. These variants integrate part of human genes into the polyproline-rich region that could introduce new post-translational modifications (PTMs), such as ubiquitination. The aim of this study was to characterize the replication capacity of different VHRVs, namely, RNF19A, ZNF787, KIF1B, EEF1A1, RNA18, RPS17, and RPL6. We used a plasmid encoding the Kernow strain, in which the fragment encoding the S17 insertion was deleted (Kernow p6 delS17) or replaced by fragments encoding the different insertions. The HEV RNA concentrations in the supernatants and the HepG2/C3A cell lysates were determined via RT-qPCR. The capsid protein ORF2 was immunostained. The effect of ribavirin was also assessed. The HEV RNA concentrations in the supernatants and the cell lysates were higher for the variants harboring the RNF19A, ZNF787, KIF1B, RPS17, and EEF1A1 insertions than for the Kernow p6 del S17, while it was not with RNA18 or RPL6 fragments. The number of ORF2 foci was higher for RNF19A, ZNF787, KIF1B, and RPS17 than for Kernow p6 del S17. VHRVs with replicative advantages were less sensitive to the antiviral effect of ribavirin. No difference in PTMs was found between VHRVs with a replicative advantage and those without. In conclusion, our study showed that insertions did not systematically confer a replicative advantage in vitro. Further studies are needed to determine the mechanisms underlying the differences in replicative capacity.

IMPORTANCE

Hepatitis E virus (HEV) is a major cause of viral hepatitis. HEV can lead to chronic infection in immunocompromised patients. Ribavirin treatment is currently used to treat such chronic infections. Recently, seven virus-host recombinant viruses were characterized in immunocompromised patients. These viruses have incorporated a portion of a human gene fragment into their genome. We studied the consequences of these insertions on the replication capacity. We found that these inserted fragments could enhance virus replication for five of the seven recombinant variants. We also showed that the recombinant variants with replicative advantages were less sensitive to ribavirin in vitro. Finally, we found that the mechanisms leading to such a replicative advantage do not seem to rely on the post-translational modifications introduced by the human gene fragment that could have modified the function of the viral protein. The mechanisms involved in improving the replication of such recombinant viruses remain to be explored.

The Full-Genome Analysis and Generation of an Infectious cDNA Clone of a Genotype 6 Hepatitis E Virus Variant Obtained from a Japanese Wild Boar: In Vitro Cultivation in Human Cell Lines

Hepatitis E virus (HEV) can cause self-limiting acute and chronic hepatitis infections, particularly in immunocompromised individuals. In developing countries, HEV is mainly transmitted via drinking contaminated water, whereas zoonotic transmission dominates the route of infection in developed countries, including Japan. Pigs are an important reservoir for HEV infection. Wild boars, which share the same genus and species as domestic pigs, are also an HEV reservoir. During our nationwide study of HEV infection in wild boar populations in Japan, a genotype 6 (HEV-6) strain, wbJHG_23, was isolated in Hyogo Prefecture in 2023. The genomic length was 7244 nucleotides, excluding the poly(A) tract. The wbJHG_23 strain exhibited the highest nucleotide identity throughout its genome with two previously reported HEV-6 strains (80.3-80.9%). Conversely, it displayed lower similarity (73.3-78.1%) with the HEV-1-5, HEV-7, and HEV-8 strains, indicating that, although closely related, the wbJHG_23 strain differs significantly from the reported HEV-6 strains and might represent a novel subtype. The wbJHG_23 strain successfully infected the human-derived cancer cell lines, PLC/PRF/5 and A549 1-1H8 cells, suggesting that HEV-6 has the potential for zoonotic infection. An infectious cDNA clone was constructed using a reverse genetics system, and a cell culture system supporting the efficient propagation of the HEV-6 strain was established, providing important tools for further studies on this genotype. Using this cell culture system, we evaluated the sensitivity of the wbJHG_23 strain to ribavirin treatment. Its good response to this treatment suggested that it could be used to treat human infections caused by HEV-6.

The molecular epidemiology of hepatitis E virus genotype 3 in Canada

Autochthonous hepatitis E virus (HEV) infection is increasingly reported in industrialized countries and is mostly associated with zoonotic HEV genotype 3 (HEV-3). In this study, we examined the molecular epidemiology of 63 human clinical HEV-3 isolates in Canada between 2014 and 2022. Fifty-five samples were IgM positive, 45 samples were IgG positive and 44 were IgM and IgG positive. The majority of the isolates belong to the subtypes 3a, 3b, and 3j, with high sequence homology to Canadian swine and pork isolates. There were a few isolates that clustered with subtypes 3c, 3e, 3f, 3h, and 3g, and an isolate from chronic infection with a rabbit strain (3ra). Previous studies have demonstrated that the isolates from pork products and swine from Canada belong to subtypes 3a and 3b, therefore, domestic swine HEV is likely responsible for the majority of clinical HEV cases in Canada and further support the hypothesis that swine serve as the main reservoirs for HEV-3 infections. Understanding the associated risk of zoonotic HEV infection requires the establishment of sustainable surveillance strategies at the interface between humans, animals, and the environment within a One-Health framework.

Prevalence of hepatitis E virus genotype 4 of probable human origin in Tibetan pigs from the Qinghai-Tibetan Plateau, China

Hepatitis E virus (HEV) is the most common cause of acute viral hepatitis worldwide. In 2018-2022, we investigated the presence of HEV RNA in 1233 stool samples collected in the Qinghai-Tibetan Plateau, including humans (16), Tibetan pigs (624), yaks (312), sheep (267), and dogs (14). HEV RNA was only detected in Tibetan pig faecal samples (18.27%, 114/624). To perform molecular characterization of HEV strains in Tibetan pigs, we obtained 21 complete HEV genome sequences between 2018 and 2022. Sequence comparisons showed that 21 HEV strains from Tibetan pigs shared the mean nucleotide identities with the reference HEV strains ranging between 82.9% and 94.9% and 89.3% and 92.1% similarities with human HEV strains. Phylogenetic analysis confirmed that all HEV strains were genotype 4, closely related to human HEV strains. Sequence recombinant analysis showed five potential recombinant strains identified in this study, of which SWU/D18/2018 (GenBank No. MK410044) was recombinant with human and swine HEV strains, located 6509-6878 nt from the recombination point. Based on the Bayesian evolutionary trees, we found that most HEV strains diverged later than human HEV (16 Tibetan pig HEV strains diverged later than 1979, and seven human HEV strains diverged earlier than 1979). Therefore, we speculated that the prevalence of HEV 4 in Tibetan pigs possibly originated from humans in the Qinghai-Tibetan Plateau.

Assessing the efficacy of different bead-based assays in capturing hepatitis E virus

Hepatitis E virus (HEV) generally causes acute liver infection in humans and its transmission could be waterborne, foodborne, bloodborne, or zoonotic. To date, there is no standard method for the detection of HEV from food and environmental samples. Herein, we explored the possibility of using magnetic beads for the capture and detection of HEV. For this purpose, we employed Dynabeads M-270 Epoxy magnetic beads, coated with different monoclonal antibodies (mAbs) against HEV capsid protein, and the Nanotrap Microbiome A Particle magnetic beads, which are coated with chemical affinity baits, to capture HEV-3 particles in suspension. Viral RNA was extracted by heat-shock or QIAamp viral RNA kit and subjected to quantification using digital-droplet RT-PCR (ddRT-PCR). We demonstrated that the mAb-coupled Dynabeads and the Nanotrap particles, both were able to successfully capture HEV-3. The latter, however had lower limit of detection (<140gc compared with <1400 gc) and significantly higher extraction efficiency in comparison to the mAb-coupled Dynabeads (41.1% vs 8.8%). We have also observed that viral RNA extraction by heat-shock is less efficient compared to using highly denaturing reagents in QIAmp viral RNA extraction kit. As such, magnetic beads have the potential to be used to capture HEV virions for research and surveillance purposes.

Common and Potential Emerging Foodborne Viruses: A Comprehensive Review

Human viruses and viruses from animals can cause illnesses in humans after the consumption of contaminated food or water. Contamination may occur during preparation by infected food handlers, during food production because of unsuitably controlled working conditions, or following the consumption of animal-based foods contaminated by a zoonotic virus. This review discussed the recent information available on the general and clinical characteristics of viruses, viral foodborne outbreaks and control strategies to prevent the viral contamination of food products and water. Viruses are responsible for the greatest number of illnesses from outbreaks caused by food, and risk assessment experts regard them as a high food safety priority. This concern is well founded, since a significant increase in viral foodborne outbreaks has occurred over the past 20 years. Norovirus, hepatitis A and E viruses, rotavirus, astrovirus, adenovirus, and sapovirus are the major common viruses associated with water or foodborne illness outbreaks. It is also suspected that many human viruses including Aichi virus, Nipah virus, tick-borne encephalitis virus, H5N1 avian influenza viruses, and coronaviruses (SARS-CoV-1, SARS-CoV-2 and MERS-CoV) also have the potential to be transmitted via food products. It is evident that the adoption of strict hygienic food processing measures from farm to table is required to prevent viruses from contaminating our food.

First detection and characterization of hepatitis E virus (Rocahepevirus ratti) from urban Norway rats (Rattus norvegicus) in the Republic of Korea

Hepatitis E virus (HEV), an emerging zoonotic pathogen, poses a significant public health concern worldwide. Recently, rat HEV (Rocahepevirus ratti genotype C1; HEV-C1) has been reported to cause zoonotic infections and hepatitis in humans. Human infections with HEV-C1 are considered to be underestimated worldwide due to limited knowledge of transmission routes, genome epidemiology, and the risk assessment of zoonosis associated with these viruses. A total of 186 wild Norway rats (Rattus norvegicus) were collected from the Republic of Korea (ROK) between 2011 and 2021. The prevalence of HEV-C1 RNA was 8 of 180 (4.4%) by reverse-transcription polymerase chain reaction. We first reported three nearly whole-genome sequences of HEV-C1 newly acquired from urban rats in the ROK. Phylogenetic analysis demonstrated that Korea-indigenous HEV-C1 formed an independent genetic group with those derived from R. norvegicus rats in other countries, indicating geographical and genetic diversity. Our findings provide critical insights into the molecular prevalence, genome epidemiology, and zoonotic potential of Rocahepevirus. This report raises awareness of the presence of Rocahepevirus-related hepatitis E among physicians in the ROK.

CRISPR/Cas9 as a New Antiviral Strategy for Treating Hepatitis Viral Infections

Hepatitis is an inflammatory liver disease primarily caused by hepatitis A (HAV), B (HBV), C (HCV), D (HDV), and E (HEV) viruses. The chronic forms of hepatitis resulting from HBV and HCV infections can progress to cirrhosis or hepatocellular carcinoma (HCC), while acute hepatitis can lead to acute liver failure, sometimes resulting in fatality. Viral hepatitis was responsible for over 1 million reported deaths annually. The treatment of hepatitis caused by viral infections currently involves the use of interferon-α (IFN-α), nucleoside inhibitors, and reverse transcriptase inhibitors (for HBV). However, these methods do not always lead to a complete cure for viral infections, and chronic forms of the disease pose significant treatment challenges. These facts underscore the urgent need to explore novel drug developments for the treatment of viral hepatitis. The discovery of the CRISPR/Cas9 system and the subsequent development of various modifications of this system have represented a groundbreaking advance in the quest for innovative strategies in the treatment of viral infections. This technology enables the targeted disruption of specific regions of the genome of infectious agents or the direct manipulation of cellular factors involved in viral replication by introducing a double-strand DNA break, which is targeted by guide RNA (spacer). This review provides a comprehensive summary of our current knowledge regarding the application of the CRISPR/Cas system in the regulation of viral infections caused by HAV, HBV, and HCV. It also highlights new strategies for drug development aimed at addressing both acute and chronic forms of viral hepatitis.

Rocahepevirus ratti as an Emerging Cause of Acute Hepatitis Worldwide

The hepatitis E virus (HEV) is a widespread human infection that causes mainly acute infection and can evolve to a chronic manifestation in immunocompromised individuals. In addition to the common strains of hepatitis E virus (HEV-A), known as Paslahepevirus balayani, pathogenic to humans, a genetically highly divergent rat origin hepevirus (RHEV) can cause hepatitis possessing a potential risk of cross-species infection and zoonotic transmission. Rocahepevirus ratti, formerly known as Orthohepevirus C, is a single-stranded RNA virus, recently reassigned to Rocahepevirus genus in the Hepeviridae family, including genotypes C1 and C2. RHEV primarily infects rats but has been identified as a rodent zoonotic virus capable of infecting humans through the consumption of contaminated food or water, causing both acute and chronic hepatitis cases in both animals and humans. This review compiles data concluding that 60% (295/489) of RHEV infections are found in Asia, being the continent with the highest zoonotic and transmission potential. Asia not only has the most animal cases but also 16 out of 21 human infections worldwide. Europe follows with 26% (128/489) of RHEV infections in animals, resulting in four human cases out of twenty-one globally. Phylogenetic analysis and genomic sequencing will be employed to gather global data, determine epidemiology, and assess geographical distribution. This information will enhance diagnostic accuracy, pathogenesis understanding, and help prevent cross-species transmission, particularly to humans.

Virus-Host Protein Interaction Network of the Hepatitis E Virus ORF2-4 by Mammalian Two-Hybrid Assays

Throughout their life cycle, viruses interact with cellular host factors, thereby influencing propagation, host range, cell tropism and pathogenesis. The hepatitis E virus (HEV) is an underestimated RNA virus in which knowledge of the virus-host interaction network to date is limited. Here, two related high-throughput mammalian two-hybrid approaches (MAPPIT and KISS) were used to screen for HEV-interacting host proteins. Promising hits were examined on protein function, involved pathway(s), and their relation to other viruses. We identified 37 ORF2 hits, 187 for ORF3 and 91 for ORF4. Several hits had functions in the life cycle of distinct viruses. We focused on SHARPIN and RNF5 as candidate hits for ORF3, as they are involved in the RLR-MAVS pathway and interferon (IFN) induction during viral infections. Knocking out (KO) SHARPIN and RNF5 resulted in a different IFN response upon ORF3 transfection, compared to wild-type cells. Moreover, infection was increased in SHARPIN KO cells and decreased in RNF5 KO cells. In conclusion, MAPPIT and KISS are valuable tools to study virus-host interactions, providing insights into the poorly understood HEV life cycle. We further provide evidence for two identified hits as new host factors in the HEV life cycle.

Viral Biology and Immune Privilege in the Development of Extrahepatic Manifestations During Hepatitis E Virus Infection

Hepatitis E virus (HEV) exhibits tropism toward hepatocytes and thus affects the liver; however, HEV may also affect other tissues, including the heart, kidneys, intestines, testicles, and central nervous system. To date, the pathophysiological links between HEV infection and extrahepatic manifestations have not yet been established. Considering that HEV infects multiple types of cells, the direct effects of virus replication in peripheral tissues represent a plausible explanation for extrahepatic manifestations. In addition, since the immune response is crucial in the development of the disease, the immune characteristics of affected tissues should be revisited to identify commonalities explaining the effects of the virus. This review summarizes the most recent advances in understanding the virus biology and immune-privileged status of specific tissues as major elements for HEV replication in diverse organs. These discoveries may open avenues to explain the multiple extrahepatic manifestations associated with HEV infection and ultimately to design effective strategies for infection control.

Inhibition of HEV Replication by FDA-Approved RdRp Inhibitors

Hepatitis E virus (HEV) is primarily a hepatotropic virus that is responsible for acute hepatitis E in the general population and for chronic hepatitis in immunocompromised individuals. In the absence of a globally accessible vaccine, pegylated interferon-α and ribavirin are the only antiviral agents available for the treatment of chronic patients. As viral RNA-dependent RNA polymerases (RdRps) are indispensable for RNA replication, they are considered potential drug targets. In this study, we screened some well-known RdRp inhibitor molecules, notably, favipiravir, sofosbuvir, remdesivir, filibuvir, and tegobuvir. Of these, monotherapy with favipiravir and sofosbuvir inhibited the RdRp activity with an IC50 value of 10.2 ± 4.9 and 5.2 ± 2.9 μM, respectively, compared to the reference drug ribavirin (3.5 ± 1.6 μM). Further investigation of the combination therapy showed a reduction in viral RNA copy numbers by approximately 90%. Therefore, favipiravir has an additive effect when used with sofosbuvir. Therefore, we propose that favipiravir is a promising anti-HEV drug that can be used in combination with sofosbuvir.

The phosphatidylserine receptor TIM1 promotes infection of enveloped hepatitis E virus

The hepatitis E virus (HEV) is an underestimated RNA virus of which the viral life cycle and pathogenicity remain partially understood and for which specific antivirals are lacking. The virus exists in two forms: nonenveloped HEV that is shed in feces and transmits between hosts; and membrane-associated, quasi-enveloped HEV that circulates in the blood. It is suggested that both forms employ different mechanisms for cellular entry and internalization but little is known about the exact mechanisms. Interestingly, the membrane of enveloped HEV is enriched with phosphatidylserine, a natural ligand for the T-cell immunoglobulin and mucin domain-containing protein 1 (TIM1) during apoptosis and involved in 'apoptotic mimicry', a process by which viruses hijack the apoptosis pathway to promote infection. We here investigated the role of TIM1 in the entry process of HEV. We determined that HEV infection with particles derived from culture supernatant, which are cloaked by host-derived membranes (eHEV), was significantly impaired after knockout of TIM1, whereas infection with intracellular HEV particles (iHEV) was unaffected. eHEV infection was restored upon TIM1 expression; and enhanced after ectopic TIM1 expression. The significance of TIM1 during entry was further confirmed by viral binding assay, and point mutations of the PS-binding pocket diminished eHEV infection. In addition, Annexin V, a PS-binding molecule also significantly reduced infection. Taken together, our findings support a role for TIM1 in eHEV-mediated cell entry, facilitated by the PS present on the viral membrane, a strategy HEV may use to promote viral spread throughout the infected body.

Tracing the History of Hepatitis E Virus Infection in Mexico: From the Enigmatic Genotype 2 to the Current Disease Situation

Hepatitis E virus (HEV) is the major cause of acute viral hepatitis worldwide. This virus is responsible for waterborne outbreaks in low-income countries and zoonosis transmission in industrialized regions. Initially, considered self-limiting, HEV may also lead to chronic disease, and evidence supports that infection can be considered a systemic disease. In the late 1980s, Mexico became a hot spot in the study of HEV due to one of the first virus outbreaks in Latin America related to enterically transmitted viral non-A, non-B hepatitis. Viral stool particles recovered from Mexican viral hepatitis outbreaks represented the first identification of HEV genotype (Gt) 2 (Gt2) in the world. No new findings of HEV-Gt2 have been reported in the country, whereas this genotype has been found in countries on the African continent. Recent investigations in Mexico have identified other strains (HEV-Gt1 and -Gt3) and a high frequency of anti-HEV antibodies in animal and human populations. Herein, the potential reasons for the disappearance of HEV-Gt2 in Mexico and the advances in the study of HEV in the country are discussed along with challenges in studying this neglected pathogen. These pieces of information are expected to contribute to disease control in the entire Latin American region.

Cell entry and release of quasi-enveloped human hepatitis viruses

Infectious hepatitis type A and type E are caused by phylogenetically distinct single-stranded, positive-sense RNA viruses that were once considered to be non-enveloped. However, studies show that both are released nonlytically from hepatocytes as 'quasi-enveloped' virions cloaked in host membranes. These virion types predominate in the blood of infected individuals and mediate virus spread within the liver. They lack virally encoded proteins on their surface and are resistant to neutralizing anti-capsid antibodies induced by infection, yet they efficiently enter cells and initiate new rounds of virus replication. In this Review, we discuss the mechanisms by which specific peptide sequences in the capsids of these quasi-enveloped virions mediate their endosomal sorting complexes required for transport (ESCRT)-dependent release from hepatocytes through multivesicular endosomes, what is known about how they enter cells, and the impact of capsid quasi-envelopment on host immunity and pathogenesis.

Discovery of Hepatitis E and Its Impact on Global Health: A Journey of 44 Years about an Incredible Human-Interest Story

The story of the discovery of hepatitis E originated in the late 1970s with my extreme belief that there was a hidden saga in the relationship between jaundice and pregnancy in developing countries and the opportunity for a massive epidemic of viral hepatitis, which hit the Gulmarg Kashmir region in November 1978. Based on data collected from a door-to-door survey, the existence of a new disease, epidemic non-A, non-B hepatitis, caused by a hitherto unknown hepatitis virus, was announced. This news was received by the world community with hype and skepticism. In the early 1980s, the world watched in awe as an extreme example of human self-experimentation led to the identification of VLP. In 1990, a cDNA clone from the virus responsible for epidemic non-A, non-B hepatitis was isolated. Over the years, we traversed three eras of ambiguity, hope, and hype of hepatitis E research and conducted several seminal studies to understand the biology of HEV and manifestations of hepatitis E. Many milestones have been reached on the long and winding road of hepatitis E research to understand the structure, biology, and diversity of the agent, changing the behavior of the pathogen in developed countries, and the discovery of a highly effective vaccine.

Hepatitis E Virus Infections: Epidemiology, Genetic Diversity, and Clinical Considerations

According to the World Health Organization, approximately 20 million people worldwide are infected annually with the hepatitis E virus (HEV). There are four main genotypes of HEV. Genotype 1 and genotype 2 are common in developing countries and are transmitted by contaminated water from a fecal-oral route. Genotype 3 and genotype 4 are common in developed countries and can lead to occasional transmission to humans via undercooked meat. Hepatitis E virus 1 and HEV3 can lead to fulminant hepatitis, and HEV3 can lead to chronic hepatitis and cirrhosis in immunocompromised patients. The majority of patients with HEV infection are asymptomatic and usually have spontaneous viral clearance without treatment. However, infection in immunocompromised individuals can lead to chronic HEV infection. Both acute and chronic HEV infections can have extrahepatic manifestations. No specific treatment is required for acute HEV infection, no treatment has been approved in chronic infection, and no HEV vaccine has been approved by the (United States) Food and Drug Administration. This review focuses on the molecular virology (HEV life cycle, genotypes, model systems, zoonosis), pathogenesis, clinical manifestation, and treatment of chronic HEV infection, especially in immunocompromised patients, to provide clinicians a better understanding of the global distribution of these infections and the significant effect they can have on immunocompromised patients.

1H, 13C, 15N backbone resonance assignment of apo and ADP-ribose bound forms of the macro domain of Hepatitis E virus through solution NMR spectroscopy

The genome of Hepatitis E virus (HEV) is 7.2 kilobases long and has three open reading frames. The largest one is ORF1, encoding a non-structural protein involved in the replication process, and whose processing is ill-defined. The ORF1 protein is a multi-modular protein which includes a macro domain (MD). MDs are evolutionarily conserved structures throughout all kingdoms of life. MDs participate in the recognition and removal of ADP-ribosylation, and specifically viral MDs have been identified as erasers of ADP-ribose moieties interpreting them as important players at escaping the early stages of host-immune response. A detailed structural analysis of the apo and bound to ADP-ribose state of the native HEV MD would provide the structural information to understand how HEV MD is implicated in virus-host interplay and how it interacts with its intracellular partner during viral replication. In the present study we present the high yield expression of the native macro domain of HEV and its analysis by solution NMR spectroscopy. The HEV MD is folded in solution and we present a nearly complete backbone and sidechains assignment for apo and bound states. In addition, a secondary structure prediction by TALOS + analysis was performed. The results indicated that HEV MD has a α/β/α topology very similar to that of most viral macro domains.

Development and Characterization of Efficient Cell Culture Systems for Genotype 1 Hepatitis E Virus and Its Infectious cDNA Clone

Hepatitis E virus (HEV) is a major cause of acute viral hepatitis globally. Genotype 1 HEV (HEV-1) is responsible for multiple outbreaks in developing countries, causing high mortality rates in pregnant women. However, studies on HEV-1 have been hindered by its poor replication in cultured cells. The JE04-1601S strain recovered from a Japanese patient with fulminant hepatitis E who contracted HEV-1 while traveling to India was serially passaged 12 times in human cell lines. The cell-culture-generated viruses (passage 12; p12) grew efficiently in human cell lines, but the replication was not fully supported in porcine cells. A full-length cDNA clone was constructed using JE04-1601S_p12 as a template. It was able to produce an infectious virus, and viral protein expression was detectable in the transfected PLC/PRF/5 cells and culture supernatants. Consistently, HEV-1 growth was also not fully supported in the cell culture of cDNA-derived JE04-1601S_p12 progenies, potentially recapitulating the narrow tropism of HEV-1 observed in vivo. The availability of an efficient cell culture system for HEV-1 and its infectious cDNA clone will be useful for studying HEV species tropism and mechanisms underlying severe hepatitis in HEV-1-infected pregnant women as well as for discovering and developing safer treatment options for this condition.

Absence of Hepatitis E Virus (HEV) Circulation in the Most Widespread Wild Croatian Canine Species, the Red Fox (Vulpes vulpes) and Jackal (Canis aureus moreoticus)

Hepatitis E virus (HEV) can infect a wide range of domestic and wild animals, and the identification of new host species is reported successively worldwide. Nevertheless, its zoonotic potential and natural transmission, especially in wildlife remains unclear, primarily due to the discrete nature of HEV infections. Since the red fox (Vulpus vulpus) is the most widespread carnivore worldwide, and has been recognized as a potential HEV reservoir, its role as a potent host species is of increasing interest. Another wild canine species, the jackal （Canis aureus moreoticus）, is becoming more important within the same habitat as that of the red fox since its number and geographical distribution have been rapidly growing. Therefore, we have chosen these wild species to determine their potential role in the epidemiology and persistence of HEV in the wilderness. The main reason for this is the finding of HEV and a rather high HEV seroprevalence in wild boars sharing the same ecological niche as the wild canine species, as well as the risk of the spread of HEV through red foxes into the outskirts of cities, where possible indirect and even direct contact with people are not excluded. Therefore, our study aimed to investigate the possibility of natural HEV infection of free-living wild canines, by testing samples for the presence of HEV RNA and anti-HEV antibodies to gain better epidemiological knowledge of the disease. For this purpose, 692 red fox and 171 jackal muscle extracts and feces samples were tested. Neither HEV RNA nor anti-HEV antibodies were detected. Although HEV circulation was not detected in the tested samples, to our knowledge, these are the first results that include jackals as a growing and important omnivore wildlife species for the presence of HEV infection in Europe.

Open Reading Frame 4 Is Not Essential in the Replication and Infection of Genotype 1 Hepatitis E Virus

Genotype 1 hepatitis E virus (HEV-1), unlike other genotypes of HEV, has a unique small open reading frame known as ORF4 whose function is not yet known. ORF4 is located in an out-framed manner in the middle of ORF1, which encodes putative 90 to 158 amino acids depending on the strains. To explore the role of ORF4 in HEV-1 replication and infection, we cloned the complete genome of wild-type HEV-1 downstream of a T7 RNA polymerase promoter, and the following ORF4 mutant constructs were prepared: the first construct had TTG instead of the initiation codon ATG (A2836T), introducing an M→L mutation in ORF4 and a D→V mutation in ORF1. The second construct had ACG instead of the ATG codon (T2837C), introducing an M→T mutation in ORF4. The third construct had ACG instead of the second in-frame ATG codon (T2885C), introducing an M→T mutation in ORF4. The fourth construct contained two mutations (T2837C and T2885C) accompanying two M→T mutations in ORF4. For the latter three constructs, the accompanied mutations introduced in ORF1 were all synonymous changes. The capped entire genomic RNAs were generated by in vitro transcription and used to transfect PLC/PRF/5 cells. Three mRNAs containing synonymous mutations in ORF1, i.e., T2837C^RNA, T2885C^RNA, and T2837C/T2885C^RNA, replicated normally in PLC/PRF/5 cells and generated infectious viruses that successfully infected Mongolian gerbils as the wild-type HEV-1 did. In contrast, the mutant RNA, i.e., A2836T^RNA, accompanying an amino acid change (D937V) in ORF1 generated infectious viruses upon transfection, but they replicated slower than the wild-type HEV-1 and failed to infect Mongolian gerbils. No putative viral protein(s) derived from ORF4 were detected in the wild-type HEV-1- as well as the mutant virus-infected PLC/PRF/5 cells by Western blot analysis using a high-titer anti-HEV-1 IgG antibody. These results demonstrated that the ORF4-defective HEV-1s had the ability to replicate in the cultured cells, and that these defective viruses had the ability to infect Mongolian gerbils unless the overlapping ORF1 was accompanied by non-synonymous mutation(s), confirming that ORF4 is not essential in the replication and infection of HEV-1.

Identification of two novel neutralizing nanobodies against swine hepatitis E virus

Hepatitis E virus (HEV) is thought to be a zoonotic pathogen that causes serious economic loss and threatens human health. However, there is a lack of efficient antiviral strategies. As a more promising tool for antiviral therapy, nanobodies (also named single-domain antibodies, sdAbs) exhibit higher specificity and affinity than traditional antibodies. In this study, nanobody anti-genotype four HEV open reading frame 2 (ORF2) was screened using phage display technology, and two nanobodies (nb14 and nb53) with high affinity were prokaryotically expressed. They were identified to block HEV ORF2 virus like particle (VLP) sp239 (aa 368-606) absorbing HepG2 cells in vitro. With the previously built animal model, the detection indicators of fecal shedding, viremia, seroconversion, alanine aminotransferase (ALT) levels, and liver lesions showed that nb14 could completely protect rabbits from swine HEV infection, and nb53 partially blocked swine HEV infection in rabbits. Collectively, these results revealed that nb14, with its anti-HEV neutralizing activity, may be developed as an antiviral drug for HEV.

Epidemiology and Risk Factors for Acute Viral Hepatitis in Bangladesh: An Overview

Viral infections by hepatotropic viruses can cause both acute and chronic infections in the liver, resulting in morbidity and mortality in humans. Hepatotropic viruses, including hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), hepatitis D virus (HDV), and hepatitis E virus (HEV), are the major pathogens that cause acute and chronic infections in humans. Although all of these viruses can cause acute hepatitis in humans, HAV and HEV are the predominant causative agents in Bangladesh, where the occurrence is sporadic throughout the year. In this review, we provide an overview of the epidemiology of hepatotropic viruses that are responsible for acute hepatitis in Bangladesh. Additionally, we focus on the transmission modes of these viruses and the control and prevention of infections.

First hepatitis E outbreak in Southeastern Senegal

The Rapid proliferation of traditional gold mining sites in the Kedougou region has led to massive migration of people from neighbouring West African countries and the establishment of several small villages where poor hygiene and sanitation conditions exist. In this context, a Hepatitis E virus outbreak was reported in Kedougou in 2014 with several cases among the traditional mining workers. Herein, we described epidemiological and laboratory data collected during the outbreak's investigation from February 2012 to November 2014. Any suspected, contact or probable case was investigated, clinical and epidemiological data were collected. In our study, sera were collected and tested for viral RNA and anti-Hepatitis E virus (HEV) IgM. Archived serum samples from Kedougou were retrospectively screened by real-time polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). A total of 65 water samples collected from ponds and wells surrounding gold panners' sites and habitats and 75 tissues samples from rats captured in the environment of traditional gold mining sites were also tested. A total of 1617 sera were collected from 698 suspected cases, 862 contacts and 57 persons with missing information. The median age was 20 (1-88 years-old) and the sex ratio was 1.72. An overall rate of 64.62% (1045/1617) of these patients tested positive for HEV with a high case fatality rate in pregnant women. All water samples and animal tissues tested negative for HEV. Our data help not only determining of the beginning of the HEV outbreak to March 2012, but also identifying risk factors associated to its emergence. However, there is a need to implement routine diagnosis, surveillance and training of health personnel in order to reduce mortality especially among pregnant women. In addition, further studies are needed to identify the virus reservoir and environmental risk factors for HEV in the Kedougou region.

Micro RNAs—The Small Big Players in Hepatitis E Virus Infection: A Comprehensive Review

The molecular mechanism of hepatitis E virus (HEV) pathology is still unclear. The micro RNAs (miRNAs), of host or viral origin, interfere with virus replication and host environment in order to create an appropriate condition for the production of mature HEV progeny. Understanding the biogenesis and the interference of miRNAs with HEV will help to revile the mechanism of viral pathogenesis.

A conserved viral amphipathic helix governs the replication site-specific membrane association

Positive-strand RNA viruses assemble their viral replication complexes (VRCs) on specific host organelle membranes, yet it is unclear how viral replication proteins recognize and what motifs or domains in viral replication proteins determine their destinations. We show here that an amphipathic helix, helix B in replication protein 1a of brome mosaic virus (BMV), is necessary for 1a’s localization to the nuclear endoplasmic reticulum (ER) membrane where BMV assembles its VRCs. Helix B is also sufficient to target soluble proteins to the nuclear ER membrane in yeast and plant cells. We further show that an equivalent helix in several plant- and human-infecting viruses of the Alsuviricetes class targets fluorescent proteins to the organelle membranes where they form their VRCs, including ER, vacuole, and Golgi membranes. Our work reveals a conserved helix that governs the localization of VRCs among a group of viruses and points to a possible target for developing broad-spectrum antiviral strategies.

Positive-strand RNA viruses [(+)RNA viruses] are the largest viral class that include numerous pathogens causing important diseases in humans, animals, and plants. During their infections, (+)RNA viruses assemble their viral replication complexes (VRCs), where they multiply themselves, at specific organelle membranes. An initial step to form VRCs is to target viral replication proteins to the designated organelle membranes. For brome mosaic virus (BMV), its replication protein 1a is responsible for the VRC formation at the nuclear endoplasmic reticulum (ER) membrane. We show that an amphipathic alpha-helix, helix B, in BMV 1a is necessary for the association of BMV 1a with the nuclear ER membrane and for BMV genome amplification. In addition, Helix B is sufficient to target several soluble proteins to the nuclear ER membrane in yeast and plant cells. BMV belongs to the Alsuviricetes class that includes viruses infecting humans, animals, and plants. We further show that the helix B across members of the Alsuviricetes class is sufficient to target fluorescence proteins to the designated organelle membranes. Our results reveal a conserved feature among a group of viruses in governing the associations with replication site-specific organelle membranes and point to a target to develop broad-spectrum antivirals.

Prediction of promiscuous epitopes in ORF2 of Hepatitis E virus: an In-Silico approach

Background

Vaccine development against emerging infections is essentially important for saving people from increasing viral infections. In developing countries, Hepatitis E (HEV) is a common infection affecting millions of people worldwide. Based on In-silico analysis, different approaches have been targeted.

Objectives

Rationale of this study is to design an epitope-based vaccine candidates with the help of immunoinformatics that can predict promiscuous B-cell and T-cell epitopes of the most antigenic HEV-ORF2 capsid protein.

Materials & Methods

This study suggests potential T-cell and B-cell epitopes of the highly antigenic HEV ORF2 capsid protein while using various In-silico tools such as NCBI-BLAST, Expassy, CLC workbench, Ellipro and Discotope.

Results

Potential antigenic and immunogenic CD8+ T-cell epitopes were predicted from the global consensus sequence of ORF2-HEV. Furthermore, twenty-two linear B-cell epitopes were predicted. Among these, "SLGAGPV" at position 587-593 and "LEFRNLTPGNTNTRVSRYSS" at position 306-325 were most antigenic with antigenicity score 1.4206 and 1.3600 respectively. Discontinuous B-cell epitopes were found by three-dimensional capsid protein structure. Epitopes predicted in this study reveal high antigenicity and promiscuity for HLA classes.

Conclusion

Collectively, our data suggests promiscuous epitopes that can potentially acts as new candidates for the design of HEV peptide vaccine.

Binding Adaptation of GS-441524 Diversifies Macro Domains and Downregulates SARS-CoV-2 de-MARylation Capacity

Viral infection in cells triggers a cascade of molecular defense mechanisms to maintain host-cell homoeostasis. One of these mechanisms is ADP-ribosylation, a fundamental post-translational modification (PTM) characterized by the addition of ADP-ribose (ADPr) on substrates. Poly(ADP-ribose) polymerases (PARPs) are implicated in this process and they perform ADP-ribosylation on host and pathogen proteins. Some viral families contain structural motifs that can reverse this PTM. These motifs known as macro domains (MDs) are evolutionarily conserved protein domains found in all kingdoms of life. They are divided in different classes with the viral belonging to Macro-D-type class because of their properties to recognize and revert the ADP-ribosylation. Viral MDs are potential pharmaceutical targets, capable to counteract host immune response. Sequence and structural homology between viral and human MDs are an impediment for the development of new active compounds against their function. Remdesivir, is a drug administrated in viral infections inhibiting viral replication through RNA-dependent RNA polymerase (RdRp). Herein, GS-441524, the active metabolite of the remdesivir, is tested as a hydrolase inhibitor for several viral MDs and for its binding to human homologs found in PARPs. This study presents biochemical and biophysical studies, which indicate that GS-441524 selectively modifies SARS-CoV-2 MD de-MARylation activity, while it does not interact with hPARP14 MD2 and hPARP15 MD2. The structural investigation of MD•GS-441524 complexes, using solution NMR and X-ray crystallography, discloses the impact of certain amino acids in ADPr binding cavity suggesting that F360 and its adjacent residues tune the selective binding of the inhibitor to SARS-CoV-2 MD.

Inhibition of Hepatitis E Virus Replication by Novel Inhibitor Targeting Methyltransferase

Hepatitis E Virus (HEV) is a quasi-enveloped virus having a single-stranded, positive-sense RNA genome (~7.2 kb), flanked with a 5′ methylated cap and a 3′ polyadenylated tail. The HEV open reading frame 1 (ORF1) encodes a 186-kDa polyprotein speculated to get processed and produce Methyltransferase (MTase), one of the four essential replication enzymes. In this study, we report the identification of the MTase inhibitor, which may potentially deplete its enzymatic activity, thus causing the cessation of viral replication. Using in silico screening through docking, we identified ten putative compounds, which were tested for their anti-MTase activity. This resulted in the identification of 3-(4-Hydroxyphenyl)propionic acid (HPPA), with an IC₅₀ value of 0.932 ± 0.15 μM, which could be perceived as an effective HEV inhibitor. Furthermore, the compound was tested for inhibition of HEV replication in the HEV culture system. The viral RNA copies were markedly decreased from ~3.2 × 10⁶ in untreated cells to ~4.3 × 10^2.8 copies in 800 μM HPPA treated cells. Therefore, we propose HPPA as a potential drug-like inhibitor against HEV-MTase, which would need further validation through in vivo analysis using animal models and the administration of Pharmacokinetic and Pharmacodynamic (PK/PD) studies.

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.

Sequence to structure analysis of the ORF4 protein from Hepatitis E virus

Hepatitis E virus (HEV) is the main cause of acute hepatitis worldwide. HEV accounts for up to 30% mortality rate in pregnant women, with highest incidences reported for genotype 1 (G1) HEV. The contributing factors in adverse cases during pregnancy in women due to HEV infection is still debated. The mechanism underlying the pathogenesis of viral infection is attributed to different genomic component of HEV, i.e., open reading frames (ORFs): ORF1, ORF2, ORF3 and ORF4. Recently, ORF4 has been discovered in enhancing the replication of GI isolates of HEV through regulation of an IRES-like RNA element. However, its characterization through computational methodologies remains unexplored. In this novel study, we provide comprehensive overview of ORF4 protein's genetic and molecular characteristics through analyzing its sequence and different structural levels. A total of three different datasets (Human, Rat and Ferret) of ORF4 genomes were built and comparatively analyzed. Several non-synonymous mutations in conjunction with higher entropy values were observed in rat and ferret datasets, however, limited variation was observed in human ORF4 genomes. Higher transition to tranversion ratio was observed in the ORF4 genomes. Studies have reported the association of intrinsic disordered proteins (IDP) with drug discovery due to its role in several signaling and regulatory processes through protein-protein interactions (PPIs). As PPIs are potent drug target sources, thus the ORF4 protein was explored by analyzing its polypeptide structure in order to shed light on its intrinsic disorder. Pressures that lead towards preponderance of disordered-promoting amino acid residues shaped the evolution of ORF4. The intrinsic disorder propensity analysis revealed ORF4 protein (Human) as a highly disordered protein (IDP). Predominance of coils and lack of secondary structure further substantiated our findings suggesting its involvement in binding to ligand molecules. Thus, ORF4 contributes to cellular signaling processes through protein-protein interactions, as IDPs are targets for regulation to accelerate the process of drug designing strategies against HEV infections.

Viral metagenomics unveiled extensive communications of viruses within giant pandas and their associated organisms in the same ecosystem

Cross-species transmission events were commonplace, with numerous cases of host-switching during the viral evolutionary history, but relatively little evidence for onward transmission in different species living in the same ecosystem. For understanding the communications of viruses in giant pandas (Ailuropoda melanoleuca) and their associated organisms, based on a large size of samples (N = 2305) collected between 2015 and 2020 from giant panda (N = 776) and other four giant panda-associated organisms in the same ecosystem, red pandas (N = 700), stray cats (N = 32), wild rats (N = 42), and mosquitoes (N = 755), viromics was used for the virus identification and subsequent virus traceability. The results showed that a feline panleukopenia virus (FPV) was found in giant pandas with clinical signs of vomiting and mild diarrhea. Meanwhile, the same FPV strain was also prevalent in the healthy red panda (Ailurus fulgens) population. From the viromes of the five different organisms, 250 virus genomes were determined. Our data revealed that besides FPV, other putative pathogenic viruses, such as red panda amdoparvoviruses (RPAVs) and Getah viruses (GETVs) were responsible for previous disease or death of some red pandas. We also demonstrated that a number of viruses were involved in potential interspecies jumping events between giant pandas and their associated species. Collectively, our results shed light on the genetic diversity and relationship of diverse viral pathogens in 'Giant pandas-Associated animals-Arthropods' and report some cases of possible viral host-switching among these host species living in the same ecosystem.

Chirohepevirus from Bats: Insights into Hepatitis E Virus Diversity and Evolution

Homologs of the human hepatitis E virus (HEV) have been identified in more than a dozen animal species. Some of them have been evidenced to cross species barriers and infect humans. Zoonotic HEV infections cause chronic liver diseases as well as a broad range of extrahepatic manifestations, which increasingly become significant clinical problems. Bats comprise approximately one-fifth of all named mammal species and are unique in their distinct immune response to viral infection. Most importantly, they are natural reservoirs of several highly pathogenic viruses, which have induced severe human diseases. Since the first discovery of HEV-related viruses in bats in 2012, multiple genetically divergent HEV variants have been reported in a total of 12 bat species over the last decade, which markedly expanded the host range of the HEV family and shed light on the evolutionary origin of human HEV. Meanwhile, bat-borne HEV also raised critical public health concerns about its zoonotic potential. Bat HEV strains resemble genomic features but exhibit considerable heterogeneity. Due to the close evolutionary relationships, bat HEV altogether has been recently assigned to an independent genus, Chirohepevirus. This review focuses on the current state of bat HEV and provides novel insights into HEV genetic diversity and molecular evolution.

A Modular Hepatitis E Virus Replicon System for Studies on the Role of ORF1-Encoded Polyprotein Domains

Zoonotic hepatitis E virus (HEV) infection is an emerging cause of acute viral hepatitis in developed countries. Known reservoirs of zoonotic genotype 3 (HEV-3) are mainly pigs and wild boar, and to a lesser extent rabbits and deer. Rabbit hepatitis E virus (HEV-3ra) is prevalent in rabbits worldwide and represents a particular risk for zoonotic infection. Current understanding of the molecular mechanisms of HEV pathogenesis is incomplete, particularly due to the limited availability of efficient and reliable cell culture systems. In order to identify genomic regions responsible for HEV propagation in cell culture, we developed a modular chimeric reporter replicon system based on cell culture-adapted (Kernow-C1/p6 and 47832mc) and rabbit-derived HEV strains. Replication in HepG2 cells was monitored on the basis of a Gaussia luciferase reporter gene that was inserted in place of the open reading frame (ORF) 2 of the HEV genome. Luciferase activity of rabbit HEV-derived replicons was significantly lower than that of Kernow-C1/p6 and 47832mc replicons. Serial exchanges of defined ORF1 segments within the Kernow-C1/p6 replicon backbone indicated that HEV replication in HepG2 cells is not determined by a single domain but rather by an interplay of longer segments of the ORF1-derived nonstructural polyprotein. This implies that a specific combination of viral factors is required for efficient HEV propagation in cell culture.

Intrinsically disordered regions in the rodent hepevirus proteome

Hepatitis E virus (HEV) is the causative agent of Hepatitis E infections across the world. Intrinsically disordered protein regions (IDPRs) or intrinsically disordered proteins (IDPs) are regions or proteins that are characterized by lack of definite structure. These IDPRs or IDPs play significant roles in a wide range of biological processes, such as cell cycle regulation, control of signaling pathways, etc. IDPR/IDP in proteins is associated with the virus's pathogenicity and infectivity. The prevalence of IDPR/IDP in rat HEV proteome remains undetermined. Hence, we examined the unstructured/disordered regions of the open reading frame (ORF) encoded proteins of rat HEV by analyzing the prevalence of intrinsic disorder. The intrinsic disorder propensity analysis showed that the different ORF proteins consisted of varying fraction of intrinsic disorder. The protein ORF3 was identified with maximum propensity for intrinsic disorder while the ORF6 protein had the least fraction of intrinsic disorder. The analysis revealed ORF6 as a structured protein (ORDP); ORF1 and ORF4 as moderately disordered proteins (IDPRs); and ORF3 and ORF5 as highly disordered proteins (IDPs). The protein ORF2 was found to be moderately as well as highly disordered using different predictors, thus, was categorized into both IDPR and IDP. Such disordered regions have important roles in pathogenesis and replication of viruses.

Processing and Subcellular Localization of the Hepatitis E Virus Replicase: Identification of Candidate Viral Factories

Hepatitis E virus (HEV) is the major cause of acute hepatitis worldwide. HEV is a positive-sense RNA virus expressing three open reading frames (ORFs). ORF1 encodes the ORF1 non–structural polyprotein, the viral replicase which transcribes the full-length genome and a subgenomic RNA that encodes the structural ORF2 and ORF3 proteins. The present study is focused on the replication step with the aim to determine whether the ORF1 polyprotein is processed during the HEV lifecycle and to identify where the replication takes place inside the host cell. As no commercial antibody recognizes ORF1 in HEV-replicating cells, we aimed at inserting epitope tags within the ORF1 protein without impacting the virus replication efficacy. Two insertion sites located in the hypervariable region were thus selected to tolerate the V5 epitope while preserving HEV replication efficacy. Once integrated into the infectious full-length Kernow C-1 p6 strain, the V5 epitopes did neither impact the replication of genomic nor the production of subgenomic RNA. Also, the V5-tagged viral particles remained as infectious as the wildtype particles to Huh-7.5 cells. Next, the expression pattern of the V5-tagged ORF1 was compared in heterologous expression and replicative HEV systems. A high molecular weight protein (180 kDa) that was expressed in all three systems and that likely corresponds to the unprocessed form of ORF1 was detected up to 25 days after electroporation in the p6 cell culture system. Additionally, less abundant products of lower molecular weights were detected in both in cytoplasmic and nuclear compartments. Concurrently, the V5-tagged ORF1 was localized by confocal microscopy inside the cell nucleus but also as compact perinuclear substructures in which ORF2 and ORF3 proteins were detected. Importantly, using in situ hybridization (RNAScope ®), positive and negative-strand HEV RNAs were localized in the perinuclear substructures of HEV-producing cells. Finally, by simultaneous detection of HEV genomic RNAs and viral proteins in these substructures, we identified candidate HEV factories.

Targeting Viral Methyltransferases: An Approach to Antiviral Treatment for ssRNA Viruses

Methyltransferase enzymes have been associated with different processes within cells and viruses. Specifically, within viruses, methyltransferases are used to form the 5′cap-0 structure for optimal evasion of the host innate immune system. In this paper, we seek to discuss the various methyltransferases that exist within single-stranded RNA (ssRNA) viruses along with their respective inhibitors. Additionally, the importance of motifs such as the KDKE tetrad and glycine-rich motif in the catalytic activity of methyltransferases is discussed.

Sequence to structural analysis of ORF5 protein in Norway rat Hepatitis E Virus

Hepatitis E virus (HEV) is a major causative agent of acute hepatitis in developing countries. The Norway rat HEV genome consists of six open reading frames (ORFs), i.e., ORF1, ORF2, ORF3, ORF4, ORF5 and ORF6. The additional reading frame encoded protein ORF5 is attributed to life cycle of rat HEV. The ORFF5 protein's function remains undetermined. Therefore, it is of interest to analyze the ORF5 protein for its physiochemical properties, primary structure, secondary structure, tertiary structure and functional characteristics using bioinformatics tools. Analysis of the ORF5 protein revealed it as highly unstable, hydrophilic with basic pI. The ORF5 protein consisted mostly of Arg, Pro, Ser, Leu and Gly. The 3D structural homology model of the ORF5 protein generated showed mixed α/β structural fold with predominance of coils. Structural analysis revealed the presence of clefts, pores and a tunnel. This data will help in the sequence, structure and functional annotation of ORF5.

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.

Hepatitis E Virus Infection: Neurological Manifestations and Pathophysiology

Hepatitis E virus (HEV) is the first cause of viral hepatitis in the world. While the water-borne HEV genotypes 1 and 2 are found in developing countries, HEV genotypes 3 and 4 are endemic in developed countries due to the existence of animal reservoirs, especially swine. An HEV infection produces many extra-hepatic manifestations in addition to liver symptoms, especially neurological disorders. The most common are neuralgic amyotrophy or Parsonage–Turner syndrome, Guillain–Barré syndrome, myelitis, and encephalitis. The pathophysiology of the neurological injuries due to HEV remains uncertain. The immune response to the virus probably plays a role, but direct virus neurotropism could also contribute to the pathophysiology. This review describes the main neurological manifestations and their possible pathogenic mechanisms.

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.

Molecular insights into the Y-domain of hepatitis E virus using computational analyses

Background

Hepatitis E virus (HEV) of the family Hepeviridae is a major causative agent of acute hepatitis in developing countries. The Y-domain is derived from multi-domain non-structural polyprotein encoded by open reading frame 1 (ORF1). Previous studies have demonstrated the essentiality of Y-domain sequences in HEV life cycle; however, its function remains completely unexplored. The following study was thus conceptualized to examine the detailed computational investigation for the putative Y-domain to estimate its phylogenetic assessment, physiochemical properties, structural and functional characteristics using in silico analyses.

Results

The phylogenetic assessment of Y-domain with a vast range of hosts indicated that the protein was very well conserved throughout the course of evolution. The Y-domain was found to be unstable, hydrophilic and basic in nature with high thermostability value. Structural analysis of Y-domain revealed mixed α/β structural fold of the protein having higher percentage of alpha-helices. The three-dimensional (3D) protein model generated through homology modelling revealed the presence of clefts, tunnels and pore. Gene ontology analysis predicted Y-domain protein’s involvement in several binding and catalytic activities as well as significant biological processes. Mutations in the conserved amino acids of the Y-domain suggested that it may stabilize or de-stabilize the protein structure that might affect its structure–function relationship.

Conclusions

This theoretical study will facilitate towards deciphering the role of unexplored Y-domain, thereby providing better understanding towards the pathogenesis 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.

Development and Optimization of an Enzyme Immunoassay to Detect Serum Antibodies against the Hepatitis E Virus in Pigs, Using Plant-Derived ORF2 Recombinant Protein

Hepatitis E is an emerging global disease, mainly transmitted via the fecal-oral route in developing countries, and in a zoonotic manner in the developed world. Pigs and wild boar constitute the primary Hepatitis E virus (HEV) zoonotic reservoir. Consumption of undercooked animal meat or direct contact with infected animals is the most common source of HEV infection in European countries. The purpose of this study is to develop an enzyme immunoassay (EIA) for the detection of anti-hepatitis E virus IgG in pig serum, using plant-produced recombinant HEV-3 ORF2 as an antigenic coating protein, and also to evaluate the sensitivity and specificity of this assay. A recombinant HEV-3 ORF2 110-610_6his capsid protein, transiently expressed by pEff vector in Nicotiana benthamiana plants was used to develop an in-house HEV EIA. The plant-derived HEV-3 ORF2 110-610_6his protein proved to be antigenically similar to the HEV ORF2 capsid protein and it can self-assemble into heterogeneous particulate structures. The optimal conditions for the in-house EIA (iEIA) were determined as follows: HEV-3 ORF2 110-610_6his antigen concentration (4 µg/mL), serum dilution (1:50), 3% BSA as a blocking agent, and secondary antibody dilution (1:20 000). The iEIA developed for this study showed a sensitivity of 97.1% (95% Cl: 89.9-99.65) and a specificity of 98.6% (95% Cl: 92.5-99.96) with a Youden index of 0.9571. A comparison between our iEIA and a commercial assay (PrioCHECK™ Porcine HEV Ab ELISA Kit, ThermoFisher Scientific, MA, USA) showed 97.8% agreement with a kappa index of 0.9399. The plant-based HEV-3 ORF2 iEIA assay was able to detect anti-HEV IgG in pig serum with a very good agreement compared to the commercially available kit.