Rat hepatitis E virus derived from wild rats (Rattus rattus) propagates efficiently in human hepatoma cell lines

Detection of hepatitis E virus genotype 3 in an Algerian mouse (Mus spretus) in Portugal

Virus monitoring in small mammals is central to the design of epidemiological control strategies for rodent-borne zoonotic viruses. Synanthropic small mammals are versatile and may be potential carriers of several microbial agents. In the present work, a total of 330 fecal samples of small mammals were collected at two sites in the North of Portugal and screened for zoonotic hepatitis E virus (HEV, species Paslahepevirus balayani). Synanthropic small mammal samples (n = 40) were collected in a city park of Porto and belonged to the species Algerian mouse (Mus spretus) (n = 26) and to the greater white-toothed shrew (Crocidura russula) (n = 14). Furthermore, additional samples were collected in the Northeast region of Portugal and included Algerian mouse (n = 48), greater white-toothed shrew (n = 47), wood mouse (Apodemus sylvaticus) (n = 43), southwestern water vole (Arvicola sapidus) (n = 52), Cabrera's vole (Microtus cabrerae) (n = 49) and Lusitanian pine vole (Microtus lusitanicus) (n = 51). A nested RT-PCR targeting a part of open reading frame (ORF) 2 region of the HEV genome was used followed by sequencing and phylogenetic analysis. HEV RNA was detected in one fecal sample (0.3%; 95% confidence interval, CI: 0.01-1.68) from a synanthropic Algerian mouse that was genotyped as HEV-3, subgenotype 3e. This is the first study reporting the detection of HEV-3 in a synanthropic rodent, the Algerian mouse. The identified HEV isolate is probably the outcome of either a spill-over infection from domestic pigs or wild boars, or the result of passive viral transit through the intestinal tract. This finding reinforces the importance in the surveillance of novel potential hosts for HEV with a particular emphasis on synanthropic animals.

Isolation and characterization of a novel rodent hepevirus in long-tailed dwarf hamsters (Cricetulus longicaudatus) in China

Hepeviruses have been identified in a broad range of animal hosts, including mammals, birds, and fish. In this study, rodents (n=91) from seven different species and ten pikas (Ochotona curzoniae) were collected in Qinghai Province, China. Using transcriptomic sequencing and confirmatory molecular testing, hepeviruses were detected in 27 of 45 (60 %) long-tailed dwarf hamsters (Cricetulus longicaudatus) and were undetected in other rodents and pika. The complete genome sequences from 14 representative strains were subsequently obtained, and phylogenetic analyses suggested that they represent a novel species within the genus Rocahepevirus, which we tentatively designated as Cl-2018QH. The virus was successfully isolated in human hepatoma (Huh-7) and murine fibroblast (17 Cl-1) cell lines, though both exhibited limited replication as assayed by detection of negative-sense RNA intermediates. A129 immunodeficient mice were inoculated with Cl-2018QH and the virus was consistently detected in multiple organs, despite relatively low viral loads. In summary, this study has described a novel rodent hepevirus, which enhances our knowledge of the genetic diversity of rodent hepeviruses and highlights its potential for cross-species transmission.

Cross-species transmission and animal infection model of hepatitis E virus

Zoonotic hepatitis E virus (HEV) infection is an emerging global public health concern, and understanding the dynamics of HEV transmission between animals and humans is crucial for public health. Animal models are critical to advancing the understanding of HEV pathogenesis, drug screening, vaccine development, and other related areas. Here, we provide an overview of recent studies investigating the cross-species transmission of HEV, and also delve into the current research and application of animal HEV infection models including non-human primates, rodents, pigs, and chickens, offering a comprehensive assessment of the advantages and disadvantages of each model. This review highlights the findings related to viral replication, shedding patterns, and immune response in these animal models, and discusses the implications for our understanding of HEV transmission to humans. These advancements in the field enhance our understanding of the biological traits and pathogenic mechanisms of HEV, offering robust support for the development of highly effective and targeted prevention and treatment strategies.

Molecular epidemiology and phylogeny of the emerging zoonotic virus Rocahepevirus: A global genetic analysis

Human infections with Rocahepevirus ratti genotype C1 (HEV-C1) in Hong Kong of China, Canada, Spain, and France have drawn worldwide concern towards Rocahepevirus. This study conducted a global genetic analysis of Rocahepevirus, aiming to furnish comprehensive molecular insights and promote further research. We retrieved 817 Rocahepevirus sequences from the GenBank database through October 31, 2023, categorizing them according to research, sample collection area and date, genotype, host, and sequence length. Subsequently, we conducted descriptive epidemiological, phylogenetic evolutionary, and protein polymorphism (in length and identity) analyses on these sequences. Rocahepevirus genomes were identified across twenty-eight countries, predominantly in Asia (71.73%, 586/817) and Europe (26.44%, 216/817). The HEV-C1 dominates Rocahepevirus (77.2%, 631/817), while newly discovered Rocahepevirus genotypes (C3/C4/C5 and other unclassified genotypes) were primarily identified in Europe (25/120) and China (91/120). Muridae animals (72.5%, 592/817) serve as the primary hosts for Rocahepevirus, with other hosts encompassing species from the families Soricidae, Hominidae, Mustelidae, and Cricetidae. Additionally, Rocahepevirus genomes (C1 genotype) were identified in sewage samples recently. The phylogenetic evolution of Rocahepevirus exhibits considerable variation. Specifically, HEV-C1 can be classified into at least six genetic groups (G1 to G6), with human HEV-C1 distributed across multiple evolutionary clades. The overall ORF1 and ORF2 amino acid sequence lengths were significantly different (P < 0.001) across Rocahepevirus genotypes. HEV-C1/C2/C3 and HEV-C4/C5 displayed substantial differences in amino acid sequence identity (58.4%-59.6%). The identification of Rocahepevirus genomes has expanded across numerous countries, particularly in European and Asian countries, coinciding with an expanding host range and emergence of new genotypes. The evolutionary path of Rocahepevirus is intricate, where the HEV-C1 dominates globally and internally forms multiple evolutionary groups (G1 to G6), exhibiting diverse genetic variation within human HEV-C1. Significant differences exist in the protein polymorphism (in length and identity) across Rocahepevirus genotypes. Given Rocahepevirus's shift from an animal virus to a zoonotic pathogen, worldwide cooperation in monitoring Rocahepevirus genomes is vital.

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.

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.

Mongolia Gerbils Are Broadly Susceptible to Hepatitis E Virus

Although cell culture systems for hepatitis E virus (HEV) have been established by using cell lines such as PLC/PRF/5 and A549, small-animal models for this virus are limited. Since Mongolia gerbils are susceptible to genotype 1, 3 and 4 HEV (HEV-1, HEV-3 and HEV4), we intraperitoneally inoculated Mongolia gerbils with HEV-5, HEV-7, HEV-8, rabbit HEV or rat HEV in addition to the above three genotypes to investigate the infectivity and to assess whether Mongolia gerbil is an appropriate animal model for HEV infection. The results indicated that (i) HEV-5 and rat HEV were effectively replicated in the Mongolia gerbils in the same manner as HEV-4: large amounts of the viral RNA were detected in the feces and livers, and high titers of the serum anti-HEV IgG antibodies were induced in all animals. The feces were shown to contain HEV that is infectious to naïve gerbils. Furthermore, HEV-4, HEV-5 and rat HEV were successfully transmitted to the gerbils by oral inoculation. (ii) Although the viral RNA and serum anti-HEV IgG antibodies were detected in all animals inoculated with HEV-1 and HEV-8, both titers were low. The viral RNA was detected in the feces collected from two of three HEV-3-inoculated, and one of three HEV-7-inoculated gerbils, but the titers were low. The serum antibody titers were also low. The viruses excreted into the feces of HEV-1-, HEV-3-, HEV-7- and HEV-8-inoculated gerbils failed to infect naïve Mongolia gerbils. (iii) No infection sign was observed in the rabbit HEV-inoculated gerbils. These results demonstrated that Mongolia gerbils are broadly susceptible to HEV, and their degree of sensitivity was dependent on the genotype. Mongolia gerbils were observed to be susceptible to not only HEVs belonging to HEV-A but also to rat HEV belonging to HEV-C1, and thus Mongolia gerbil could be useful as a small-animal model for cross-protection experiments between HEV-A and HEV-C1. Mongolia gerbils may also be useful for the evaluation of the efficacy of vaccines against HEV.

HuH-7-Lunet BLR Cells Propagate Rat Hepatitis E Virus (HEV) in a Cell Culture System Optimized for HEV

The family Hepeviridae comprises the species Orthohepevirus A–D (HEV-A to -D). HEV-C genotype 1 (HEV-C1, rat HEV) is able to infect humans. This study investigated whether an optimized HEV-A cell culture system is able to propagate the cell culture-derived rat HEV, and if de novo isolation of the virus from rat liver is possible. We tested the liver carcinoma cell lines PLC/PRF/5, HuH-7, and HuH-7-Lunet BLR for their susceptibility to HEV-C1 strains. Cells were infected with the cell culture-derived HEV-C1 strain R63 and rat liver-derived strain R68. Cells were maintained in MEMM medium, which was refreshed every 3–4 days. The viral load of HEV-C1 was determined by RT-qPCR in the supernatant and expressed as genome copies per mL (c/mL). Rat HEV replication was most efficient in the newly introduced HuH-7-Lunet BLR cell line. Even if the rat HEV isolate had been pre-adapted to PLC/PRF/5 by multiple passages, replication in HuH-7-Lunet BLR was still at least equally effective. Only HuH-7-Lunet BLR cells were susceptible to the isolation of HEV-C1 from the liver homogenate. These results suggest HuH-7-Lunet BLR as the most permissive cell line for rat HEV. Our HEV-C1 cell culture system may be useful for basic research, the animal-free generation of large amounts of the virus as well as for the testing of antiviral compounds and drugs.

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.

Production of capsid proteins of rat hepatitis E virus in Escherichia coli and characterization of self-assembled virus-like particles

Rat hepatitis E virus (HEV) has been isolated from wild rats worldwide and the potential of zoonotic transmission has been documented. Escherichia coli (E. coli) is utilized as an effective system for producing HEV-like particles. However, the production of rat HEV ORF2 proteins in E. coli forming virus-like particles (VLPs) has not yet been reported. In this study, nine rat HEV ORF2 proteins of the ratELOMB-131L strain with truncated N- and C-termini (amino acids 339-594, 349-594, 351-594, 354-594, 357-594, 357-599, 357-604, 357-609, and 357-614 of ORF2 protein) were expressed in E. coli and the 357-614 protein self-assembled most efficiently. A bioanalyzer showed that the purified 357-614 protein has a molecular weight of 33.5 kDa and a purity of 93.2%. Electron microscopy revealed that the purified 33.5 kDa protein formed VLPs with a diameter of 21-52 (average 32) nm, and immunoelectron microscopy using an anti-rat HEV ORF2 monoclonal antibody (TA7014) indicated that the observed VLPs were derived from rat HEV ORF2. The VLPs attached to and entered the PLC/PRF/5 cells and blocked the neutralization of rat HEV by TA7014, suggesting that the VLPs possess the antigenic structure of infectious rat HEV particles. In addition, rat HEV VLPs showed high immunogenicity in mice. The present results would be useful for future studies on the development of VLP-based vaccines for HEV prevention in a rat model and for the prevention of rat HEV infection in humans.

Multimodal investigation of rat hepatitis E virus antigenicity: Implications for infection, diagnostics, and vaccine efficacy

BACKGROUND & AIMS

Rat hepatitis E virus (Orthohepevirus species C; HEV-C1) is an emerging cause of viral hepatitis in humans. HEV-C1 is divergent from other HEV variants infecting humans that belong to Orthohepevirus species A (HEV-A). This study assessed HEV-C1 antigenic divergence from HEV-A and investigated the impact of this divergence on infection susceptibility, serological test sensitivity, and vaccine efficacy.

METHODS

Immunodominant E2s peptide sequences of HEV-A and HEV-C1 were aligned. Interactions of HEV-C1 E2s and anti-HEV-A monoclonal antibodies (mAbs) were modeled. Recombinant peptides incorporating E2s of HEV-A (HEV-A4 p239) and HEV-C1 (HEV-C1 p241) were expressed. HEV-A and HEV-C1 patient sera were tested using antibody enzymatic immunoassays (EIA), antigen EIAs, and HEV-A4 p239/HEV-C1 p241 immunoblots. Rats immunized with HEV-A1 p239 vaccine (Hecolin), HEV-A4 p239 or HEV-C1 p241 peptides were challenged with a HEV-C1 strain.

RESULTS

E2s sequence identity between HEV-A and HEV-C1 was only 48%. There was low conservation at E2s residues (23/53; 43.4%) involved in mAb binding. Anti-HEV-A mAbs bound HEV-C1 poorly in homology modeling and antigen EIAs. Divergence resulted in low sensitivity of commercial antigen (0%) and antibody EIAs (10-70%) for HEV-C1 diagnosis. Species-specific HEV-A4 p239/HEV-C1 p241 immunoblots accurately differentiated HEV-A and HEV-C1 serological profiles in immunized rats (18/18; 100%) and infected-patient sera (32/36; 88.9%). Immunization with Hecolin and HEV-A4 p239 was partially protective while HEV-C1 p241 was fully protective against HEV-C1 infection in rats.

CONCLUSIONS

Antigenic divergence significantly decreases sensitivity of hepatitis E serodiagnostic assays for HEV-C1 infection. Species-specific immunoblots are useful for diagnosing HEV-C1 and for differentiating the serological profiles of HEV-A and HEV-C1. Prior HEV-A exposure is not protective against HEV-C1. HEV-C1 p241 is an immunogenic vaccine candidate against HEV-C1.

LAY SUMMARY

Rat hepatitis E virus (HEV-C1) is a new cause of hepatitis in humans. Using a combination of methods, we showed that HEV-C1 is highly divergent from the usual cause of human hepatitis (HEV-A). This divergence reduces the capacity of existing tests to diagnose HEV-C1 and also indicates that prior exposure to HEV-A (via infection or vaccination) is not protective against HEV-C1.

Review of Hepatitis E Virus in Rats: Evident Risk of Species Orthohepevirus C to Human Zoonotic Infection and Disease

Hepatitis E virus (HEV) (family Hepeviridae) is one of the most common human pathogens, causing acute hepatitis and an increasingly recognized etiological agent in chronic hepatitis and extrahepatic manifestations. Recent studies reported that not only are the classical members of the species Orthohepevirus A (HEV-A) pathogenic to humans but a genetically highly divergent rat origin hepevirus (HEV-C1) in species Orthohepevirus C (HEV-C) is also able to cause zoonotic infection and symptomatic disease (hepatitis) in humans. This review summarizes the current knowledge of hepeviruses in rodents with special focus of rat origin HEV-C1. Cross-species transmission and genetic diversity of HEV-C1 and confirmation of HEV-C1 infections and symptomatic disease in humans re-opened the long-lasting and full of surprises story of HEV in human. This novel knowledge has a consequence to the epidemiology, clinical aspects, laboratory diagnosis, and prevention of HEV infection in humans.

Orthohepevirus C: An Expanding Species of Emerging Hepatitis E Virus Variants

Hepatitis E virus (HEV) is an emerging zoonotic pathogen that has received an increasing amount of attention from virologists, clinicians, veterinarians, and epidemiologists over the past decade. The host range and animal reservoirs of HEV are rapidly expanding and a plethora of emerging HEV variants have been recently identified, some of which have the potential for interspecies infection. In this review, the detection of genetically diverse HEV variants, classified into and presumably associated with the species Orthohepevirus C, currently comprising HEV genotypes C1 and C2, by either serological or molecular approach is summarized. The distribution, genomic variability, and evolution of Orthohepevirus C are analyzed. Moreover, the potential risk of cross-species infection and zoonotic transmission of Orthohepevirus C are discussed.

Multivesicular body sorting and the exosomal pathway are required for the release of rat hepatitis E virus from infected cells

Recent reports have shown that rat hepatitis E virus (HEV) is capable of infecting humans. We also successfully propagated rat HEV into human PLC/PRF/5 cells, raising the possibility of a similar mechanism shared by human HEV and rat HEV. Rat HEV has the proline-rich sequence, PxYPMP, in the open reading frame 3 (ORF3) protein that is indispensable for its release. However, the release mechanism remains unclear. The overexpression of dominant-negative (DN) mutant of vacuolar protein sorting (Vps)4A or Vps4B decreased rat HEV release to 23.9 % and 18.0 %, respectively. The release of rat HEV was decreased to 8.3 % in tumor susceptibility gene 101 (Tsg101)-depleted cells and to 31.5 % in apoptosis-linked gene 2-interacting protein X (Alix)-depleted cells. Although rat HEV ORF3 protein did not bind to Tsg101, we found a 90-kDa protein capable of binding to wild-type rat HEV ORF3 protein but not to ORF3 mutant with proline to leucine mutations in the PxYPMP motif. Rat HEV release was also decreased in Ras-associated binding 27A (Rab27A)- or hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs)-depleted cells (to 20.1 % and 18.5 %, respectively). In addition, the extracellular rat HEV levels in the infected PLC/PRF/5 cells were increased after treatment with Bafilomycin A1 and decreased after treatment with GW4869. These results indicate that rat HEV utilizes multivesicular body (MVB) sorting for its release and that the exosomal pathway is required for rat HEV egress. A host protein alternative to Tsg101 that can bind to rat HEV ORF3 should be explored in further study.

Small Animal Models of Hepatitis E Virus Infection

Novel hepeviruses have been recovered from many different animal species in recent years, increasing the diversity known to exist among the Hepeviridae, which now include two genera, Piscihepevirus and Orthohepevirus Multiple viral genotypes in the Orthohepevirus A species are able to replicate and cause acute hepatitis E in humans, and thus represent an important public health problem in industrialized as well as developing countries. Although hepatitis E virus (HEV) infections typically result in acute and self-limited hepatitis, immunocompromised and transplant patients are vulnerable to prolonged infections and to chronic hepatitis. Cell culture systems have been established for several HEV strains and offer new opportunities for the study of HEV biology. Similarly, a variety of new small animal models have been developed, using either nonhuman hepeviruses in their cognate hosts as surrogates for human HEV, or human HEV infection of immunodeficient mice with chimeric livers engrafted with human hepatocytes. These new models provide several advantages over previous nonhuman primate models of hepatitis E infection and will facilitate studies of pathogenicity, cross-species infection, mechanisms of virus replication, and vaccine and antiviral agent development. This article reviews the current understanding of small animal models for HEV.

Antiviral candidates against the hepatitis E virus (HEV) and their combinations inhibit HEV growth in in vitro

Hepatitis E is a global public health problem. Ribavirin (RBV) and pegylated interferon alpha are currently administered to cure hepatitis E. Recently, in combination with RBV, sofosbuvir (SOF), an anti-hepatitis C virus nucleotide analog, is also given to patients with chronic hepatitis E. However, this combinatorial therapy sometimes fails to achieve a sustained virological response. In this study, we used 27 antiviral compounds, including 15 nucleos(t)ide analogs, for in vitro screening against a genotype 3 HEV strain containing a Gaussia luciferase reporter. RBV, SOF, 2'-C-methyladenosine, 2'-C-methylcytidine (2CMC), 2'-C-methylguanosine (2CMG), and two 4'-azido nucleoside analogs (R-1479 and RO-9187) suppressed replication of the reporter genome, while only RBV, SOF, 2CMC and 2CMG inhibited the growth of genotype 3 HEV in cultured cells. Although 2CMG and RBV (2CMG/RBV) exhibited a synergistic effect while SOF/RBV and 2CMC/RBV showed antagonistic effects on the reporter assay, these three nucleos(t)ide analogs acted additively with RBV in inhibiting HEV growth in cultured cells. Furthermore, SOF and 2CMG, with four interferons (IFN-α2b, IFN-λ1, IFN-λ2 and IFN-λ3), inhibited HEV growth efficiently and cleared HEV in cultured cells. These results suggest that, in combination with RBV or interferons, SOF and 2CMG would be promising bases for developing anti-HEV nucleos(t)ide analogs.

First detection of Hepatitis E virus (Orthohepevirus C) in wild brown rats (Rattus norvegicus) from Great Britain

In the United Kingdom, there has been an increase in the number of hepatitis E virus (HEV) infections in people annually since 2010. Most of these are thought to be indigenously acquired Orthohepevirus A genotype 3 (HEV G3), which has been linked to pork production and consumption. However, the dominant subgroup circulating in British pigs differs from that which is found in people; therefore, an alternative, potentially zoonotic, source is suspected as a possible cause of these infections. Rodents, brown rats (Rattus norvegicus) in particular, have been shown to carry HEV, both the swine HEV G3 genotype and Orthohepevirus C, genotype C1 (rat HEV). To investigate the prevalence of HEV in British rodents, liver tissue was taken from 307 rodents collected from pig farms (n = 12) and other locations (n = 10). The RNA from these samples was extracted and tested using a pan‐HEV nested RT‐PCR. Limited histopathology was also performed. In this study, 8/61 (13%, 95% CI, 5–21) of brown rat livers were positive for HEV RNA. Sequencing of amplicons demonstrated all infections to be rat HEV with 87%–92% nucleotide identity to other rat HEV sequences circulating within Europe and China (224 nt ORF‐1). Lesions and necrosis were observed histologically in 2/3 samples examined. No rat HEV RNA was detected in any other species, and no HEV G3 RNA was detected in any rodent in this study. This is the first reported detection of rat HEV in Great Britain. A human case of rat HEV infection has recently been reported in Asia, suggesting that rat HEV could pose a risk to public health.

Cell culture systems for the study of hepatitis E virus

Hepatitis E virus (HEV) is the causative agent of hepatitis E in humans and is the leading cause of enterically-transmitted viral hepatitis worldwide. Increasing numbers of HEV infections, together with no available specific anti-HEV treatment, contributes to the pathogen's major health burden. A robust cell culture system is required for virologic studies and the development of new antiviral drugs. Unfortunately, like other hepatitis viruses, HEV is difficult to propagate in conventional cell lines. Many different cell culture systems have been tested using various HEV strains, but viral replication usually progresses very slowly, and infection with low virion counts results in non-productive HEV replication. However, recent progress involving generation of cDNA clones and passaging primary patient isolates in distinct cell lines has improved in vitro HEV propagation. This review describes various approaches to cultivate HEV in cellular and animal models and how these systems are used to study HEV infections and evaluate anti-HEV drug candidates.

The prevalence and genomic characteristics of hepatitis E virus in murine rodents and house shrews from several regions in China

Background

Urban rodents and house shrews are closely correlated in terms of location with humans and can transmit many pathogens to them. Hepatitis E has been confirmed to be a zoonotic disease. However, the zoonotic potential of rat HEV is still unclear. The aim of this study was to determine the prevalence and genomic characteristics of hepatitis E virus (HEV) in rodents and house shrews.

Results

We collected a total of 788 animals from four provinces in China. From the 614 collected murine rodents, 20.19% of the liver tissue samples and 45.76% of the fecal samples were positive for HEV. From the 174 house shrews (Suncus murinus), 5.17% fecal samples and 0.57% liver tissue samples were positive for HEV. All of the HEV sequences obtained in this study belonged to Orthohepevirus C1. However, we observed a lower percentage of identity in the ORF3 region upon comparing the amino acid sequences between Rattus norvegicus and Rattus losea. HEV derived from house shrews shared a high percentage of identity with rat HEV. Notably, the first near full-length of the HEV genome from Rattus losea is described in our study, and we also report the first near full-length rat HEV genomes in Rattus norvegicus from China.

Conclusion

HEV is prevalent among the three common species of murine rodents (Rattus. norvegicus, Rattus. tanezumi, and Rattus. losea) in China. HEV sequences detected from house shrews were similar to rat HEV sequences. The high identity of HEV from murine rodents and house shrews suggested that HEV can spread among different animal species.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1746-z) contains supplementary material, which is available to authorized users.

Genotype 5 Hepatitis E Virus Produced by a Reverse Genetics System Has the Potential for Zoonotic Infection

Neither an animal model nor a cell culture system has been established for the genotype 5 hepatitis E virus (G5 HEV), and the pathogenicity, epidemiology, and replication mechanism of the virus remain unclear. In this study, we used a reverse genetics system to generate G5 HEV and examined the possibility of zoonotic infection. Capped and uncapped genomic G5 HEV RNAs generated by in vitro transcription were transfected into PLC/PRF/5 cells. Infectious G5 HEV was recovered from the capped G5 HEV RNA–transfected PLC/PRF/5 cells and the subsequently passaged cells. G5 HEV was also recovered from uncapped G5 HEV–transfected PLC/PRF/5 cells after a longer lag phase, suggesting that the 5′‐cap structure is not essential but affected the efficiency of G5 HEV replication. G5 HEV infection was neutralized not only by anti‐G5 HEV‐like particles (HEV‐LPs) antibody, but also by anti‐G1, anti‐G3, anti‐G4, and anti‐G7 HEV‐LPs antibodies. G5 HEV was capable of infecting cynomolgus monkeys negative for anti‐HEV antibody but not animals positive for anti‐G7 HEV immunoglobulin G (IgG), indicating that cynomolgus monkeys were susceptible to G5 HEV, and the serotype of G5 HEV was identical to that of G7 HEV and human HEVs. Moreover, G5 HEV replication was efficiently inhibited by ribavirin and partially inhibited by sofosbuvir. Conclusion: Infectious G5 HEV was produced using a reverse genetics system, and the antigenicity was identical to that of human HEVs and G7 HEV. Transmission of G5 HEV to primates was confirmed by an experimental infection, providing evidence of the possibility of zoonotic infection by G5 HEV.

Hepatitis E virus in Common voles (Microtus arvalis) from an urban environment, Hungary: Discovery of a Cricetidae-specific genotype of Orthohepevirus C

Hepatitis E virus is a major causative agent of acute hepatitis worldwide. Despite its zoonotic potential, there is limited information about the natural chain of hepevirus infection in wildlife, and the potential reservoir species. In this study, we performed a HEV survey by heminested RT-PCR on rodent samples from an urban environment (in the city of Pécs, Hungary) and investigated the prevalence of the virus among these native rodent species (Apodemus agrarius, Apodemus flavicollis, Apodemus sylvaticus, Microtus arvalis and Myodes glareolus). HEV was detected exclusively in Common voles (M. arvalis), in 10.2% of screened voles, and 3.2% of all investigated samples from all species. Based on the phylogenetic analysis, our strain showed the closest homology with European Orthohepevirus C strains detected previously in faecal samples of birds of prey and Red fox, supporting the possibility of the dietary origin of these strains. In addition, our samples showed close phylogenetic relation with a South American strain detected in Necromys lasiurus (Cricetidae), but separated clearly from other Muridae-associated strains, suggesting the presence of a Cricetidae-specific genotype in Europe and South-America. Based on these results, we hypothesize the reservoir role of M. arvalis rodents for the European Cricetidae-specific Orthohepevirus C genotype.

Hepatitis E Virus: Animal Models and Zoonosis

Hepatitis E virus (HEV) is an important human pathogen that historically has been difficult to study. Limited levels of replication in vitro hindered our understanding of the viral life cycle. Sporadic and low-level virus shedding, lack of standardized detection methods, and subclinical infections made the development of animal models difficult. Better diagnostic techniques and understanding of the virus increased our ability to identify and characterize animal strains and animals that are amenable to model human-relevant infection. These advances are translating into the development of useful HEV animal models so that some of the greatest concerns associated with HEV infection, including host immunology, chronic infection, severe pregnancy mortality, and extrahepatic manifestations, can now be studied. Continued development of these animal models will be instrumental in understanding the many complex questions associated with HEV infection and for assessing therapeutics and prevention strategies to minimize HEV becoming a greater risk to the human population.

Potential Approaches to Assess the Infectivity of Hepatitis E Virus in Pork Products: A Review

The zoonotic transmission of hepatitis E, caused by the hepatitis E virus (HEV), is an emerging issue. HEV appears common in pigs (although infected pigs do not show clinical signs), and evidence suggests that a number of hepatitis E cases have been associated with the consumption of undercooked pork meat and products. Little information is available on whether cooking can eliminate HEV, since there is currently no robust method for measuring its infectivity. HEV infectivity can be clearly demonstrated by monitoring for signs of infection (e.g., shedding of virus) in an animal model. However, this approach has several disadvantages, such as lack of reproducibility and unsuitability for performing large numbers of tests, high costs, and not least ethical considerations. Growth in cell culture can unambiguously show that a virus is infectious and has the potential for replication, without the disadvantages of using animals. Large numbers of tests can also be performed, which can make the results more amenable to statistical interpretation. However, no HEV cell culture system has been shown to be applicable to all HEV strains, none has been standardized, and few studies have demonstrated their use for measurement of HEV infectivity in food samples. Nonetheless, cell culture remains the most promising approach, and the main recommendation of this review is that there should be an extensive research effort to develop and validate a cell culture-based method for assessing HEV infectivity in pork products. Systems comprising promising cell lines and HEV strains which can grow well in cell culture should be tested to select an assay for effective and reliable measurement of HEV infectivity over a wide range of virus concentrations. The assay should then be harnessed to a procedure which can extract HEV from pork products, to produce a method suitable for further use. The method can then be used to determine the effect of heat or other elimination processes on HEV in pork meat and products, or to assess whether HEV detected in any surveyed foodstuffs is infectious and therefore poses a risk to public health.

Detection of rat hepatitis E virus in wild Norway rats (Rattus norvegicus) and Black rats (Rattus rattus) from 11 European countries

Rat hepatitis E virus (HEV) is genetically only distantly related to hepeviruses found in other mammalian reservoirs and in humans. It was initially detected in Norway rats (Rattus norvegicus) from Germany, and subsequently in rats from Vietnam, the USA, Indonesia, China, Denmark and France. Here, we report on a molecular survey of Norway rats and Black rats (Rattus rattus) from 12 European countries for ratHEV and human pathogenic hepeviruses. RatHEV-specific real-time and conventional RT-PCR investigations revealed the presence of ratHEV in 63 of 508 (12.4%) rats at the majority of sites in 11 of 12 countries. In contrast, a real-time RT-PCR specific for human pathogenic HEV genotypes 1-4 and a nested broad-spectrum (NBS) RT-PCR with subsequent sequence determination did not detect any infections with these genotypes. Only in a single Norway rat from Belgium a rabbit HEV-like genotype 3 sequence was detected. Phylogenetic analysis indicated a clustering of all other novel Norway and Black rat-derived sequences with ratHEV sequences from Europe, the USA and a Black rat-derived sequence from Indonesia within the proposed ratHEV genotype 1. No difference in infection status was detected related to age, sex, rat species or density of human settlements and zoological gardens. In conclusion, our investigation shows a broad geographical distribution of ratHEV in Norway and Black rats from Europe and its presence in all settlement types investigated.

Genetic and physicochemical analyses of a novel ferret hepatitis E virus, and clinical signs of infection after birth

A novel cluster of five ferret hepatitis E virus (HEV) strains was detected from nine laboratory ferrets (Mustela putorius furo) imported from a ferret farm in the U.S. Our detection of ferret HEV RNA and anti-HEV antibodies, and alanine aminotransferase (ALT) value assessment indicated that all of the 9 ferrets were infected with ferret HEV, and that the infection exhibited three patterns: sub-clinical infection (n=2), acute hepatitis (n=6) and persistent infection (n=1). Next-generation sequence analyses of the entire genome sequences of the five strains revealed that their nucleotide sequence identities ranged from 99.5% to 99.9%, indicating that genetically similar ferret HEVs had been circulating at this the U.S. ferret farm. In contrast, the strains shared 82% and 89% nucleotide sequence identities with other ferret HEV that isolated from the Netherlands (JN998607) and the U.S. (AB890374), suggesting that these strains form a novel cluster of ferret HEV with diverse genomes depending on the region where their host. Particles with a diameter of ~35nm at a density of 1.201g/cm³ were observed in the fecal specimens by electron microscopy. There was no evidence that the particles were associated with the cell membrane. The ferret HEV RNA was not constantly detected in urine, suggesting that the excretion of ferret HEV into urine is not a common feature of HEV infection.

Production of infectious dromedary camel hepatitis E virus by a reverse genetic system: Potential for zoonotic infection

BACKGROUND & AIMS

The pathogenicity, epidemiology and replication mechanism of dromedary camel hepatitis E virus (DcHEV), a novel hepatitis E virus (HEV), has been unclear. Here we used a reverse genetic system to produce DcHEV and examined the possibility of zoonotic infection.

METHODS

Capped genomic RNA derived from a synthetic DcHEV cDNA was transfected into human hepatocarcinoma cells PLC/PRF/5. The DcHEV capsid protein and RNA were detected by an enzyme-linked immunosorbent assay (ELISA) or RT-qPCR. A neutralization test for DcHEV was carried out by using antisera against HEV-like particles. DcHEV was used to inoculate two cynomolgus monkeys to examine the potential for cross-species infection.

RESULTS

The transfection of PLC/PRF/5 cells with capped DcHEV RNA resulted in the production of infectious DcHEV. The genome sequence analysis demonstrated that both nucleotide and amino acid changes accumulated during the passages in PLC/PRF/5 cells. The cynomolgus monkeys showed serological signs of infection when DcHEV was intravenously inoculated. DcHEV was neutralized by not only anti-DcHEV-LPs antibody, but also anti-genotype 1 (G1), G3 and G4 HEV-LPs antibodies. Moreover, the monkeys immunized with DcHEV escaped the G3 HEV challenge, indicating that the serotype of DcHEV is similar to those of other human HEVs.

CONCLUSIONS

Infectious DcHEV was produced using a reverse genetic system and propagated in PLC/PRF/5 cells. The antigenicity and immunogenicity of DcHEV are similar to those of G1, G3 and G4 HEV. DcHEV was experimentally transmitted to primates, demonstrating the possibility of a zoonotic infection by DcHEV.

LAY SUMMARY

Dromedary camel hepatitis E virus (DcHEV) was produced by a reverse genetic system and grows well in PLC/PRF/5 cells. Cynomolgus monkeys experimentally infected with DcHEV indicated serological signs of infection, suggesting that DcHEV has the potential to cause zoonotic HEV infection.

Epizootiological study of rodent-borne hepatitis E virus HEV-C1 in small mammals in Hanoi, Vietnam

There is concern about the zoonotic potential of rodent-borne hepatitis E virus, designated as HEV-C1. However, epizootiological information about HEV-C1 is limited. To address this issue, serum samples from 443 small mammals captured at 5 sites in Hanoi, Vietnam, were examined for anti-HEV-C1 IgG antibodies. In addition, livers of seropositive animals were examined for viral RNA. Anti-HEV-C1 antibodies were detected in 57 (12.9%) of the 443 serum samples. Seropositive animals were found in all of the sites (4.7% to 22.2%). Anti-HEV-C1 antibodies were detected from 48 (12.3%) of 389 Rattus norvegicus and 9 (19.6%) of 46 R. tanezumi, but were not detected from 8 Suncus murinus. Viral RNAs were detected from 13 (22.8%) of the 57 seropositive rodents. The detection rate of viral RNA in seropositive R. tanezumi (66.7%, 6/9) was significantly higher than that in seropositive R. norvegicus (14.6%, 7/48). The results suggest that R. tanezumi is more susceptible than R. norvegicus to HEV-C1 infection. Phylogenetic analysis revealed that Vietnamese strains were divided into 3 clusters in genetic group 2 of HEV-C1. Multiple clusters of viruses were detected at several sites without species specificity, suggesting that 3 clusters of HEV-C1 co-circulate in Hanoi, Vietnam.

Molecular Biology and Infection of Hepatitis E Virus

Hepatitis E virus (HEV) is a viral pathogen transmitted primarily via fecal-oral route. In humans, HEV mainly causes acute hepatitis and is responsible for large outbreaks of hepatitis across the world. The case fatality rate of HEV-induced hepatitis ranges from 0.5 to 3% in young adults and up to 30% in infected pregnant women. HEV strains infecting humans are classified into four genotypes. HEV strains from genotypes 3 and 4 are zoonotic, whereas those from genotypes 1 and 2 have no known animal reservoirs. Recently, notable progress has been accomplished for better understanding of HEV biology and infection, such as chronic HEV infection, in vitro cell culture system, quasi-enveloped HEV virions, functions of the HEV proteins, mechanism of HEV antagonizing host innate immunity, HEV pathogenesis and vaccine development. However, further investigation on the cross-species HEV infection, host tropism, vaccine efficacy, and HEV-specific antiviral strategy is still needed. This review mainly focuses on molecular biology and infection of HEV and offers perspective new insight of this enigmatic virus.

High diversity of picornaviruses in rats from different continents revealed by deep sequencing

Outbreaks of zoonotic diseases in humans and livestock are not uncommon, and an important component in containment of such emerging viral diseases is rapid and reliable diagnostics. Such methods are often PCR-based and hence require the availability of sequence data from the pathogen. Rattus norvegicus (R. norvegicus) is a known reservoir for important zoonotic pathogens. Transmission may be direct via contact with the animal, for example, through exposure to its faecal matter, or indirectly mediated by arthropod vectors. Here we investigated the viral content in rat faecal matter (n=29) collected from two continents by analyzing 2.2 billion next-generation sequencing reads derived from both DNA and RNA. Among other virus families, we found sequences from members of the Picornaviridae to be abundant in the microbiome of all the samples. Here we describe the diversity of the picornavirus-like contigs including near-full-length genomes closely related to the Boone cardiovirus and Theiler's encephalomyelitis virus. From this study, we conclude that picornaviruses within R. norvegicus are more diverse than previously recognized. The virome of R. norvegicus should be investigated further to assess the full potential for zoonotic virus transmission.

A rat model for hepatitis E virus

Hepatitis E virus (HEV) is one of the prime causes of acute viral hepatitis, and chronic hepatitis E is increasingly recognized as an important problem in the transplant setting. Nevertheless, the fundamental understanding of the biology of HEV replication is limited and there are few therapeutic options. The development of such therapies is partially hindered by the lack of a robust and convenient animal model. We propose the infection of athymic nude rats with the rat HEV strain LA-B350 as such a model. A cDNA clone, pLA-B350, was constructed and the infectivity of its capped RNA transcripts was confirmed in vitro and in vivo. Furthermore, a subgenomic replicon, pLA-B350/luc, was constructed and validated for in vitro antiviral studies. Interestingly, rat HEV proved to be less sensitive to the antiviral activity of α-interferon, ribavirin and mycophenolic acid than genotype 3 HEV (a strain that infects humans). As a proof-of-concept, part of the C-terminal polymerase sequence of pLA-B350/luc was swapped with its genotype 3 HEV counterpart: the resulting chimeric replicon replicated with comparable efficiency as the wild-type construct, confirming that LA-B350 strain is amenable to humanization (replacement of certain sequences or motifs by their counterparts from human HEV strains). Finally, ribavirin effectively inhibited LA-B350 replication in athymic nude rats, confirming the suitability of the rat model for antiviral studies.

Summary: Rat hepatitis E virus strain LA-B350 is used as a model for antiviral studies for hepatitis E virus using a cDNA clone, replicon and in vivo studies.

Update on hepatitis E virology: Implications for clinical practice

Hepatitis E virus (HEV) is a positive-strand RNA virus transmitted by the fecal-oral route. The 7.2kb genome encodes three open reading frames (ORF) which are translated into (i) the ORF1 polyprotein, representing the viral replicase, (ii) the ORF2 protein, corresponding to the viral capsid, and (iii) the ORF3 protein, a small protein involved in particle secretion. Although HEV is a non-enveloped virus in bile and feces, it circulates in the bloodstream wrapped in cellular membranes. HEV genotypes 1 and 2 infect only humans and cause mainly waterborne outbreaks. HEV genotypes 3 and 4 are widely represented in the animal kingdom and are transmitted as a zoonosis mainly via contaminated meat. HEV infection is usually self-limited but may persist and cause chronic hepatitis in immunocompromised patients. Reduction of immunosuppressive treatment or antiviral therapy with ribavirin have proven effective in most patients with chronic hepatitis E but therapy failures have been reported. Alternative treatment options are needed, therefore. Infection with HEV may also cause a number of extrahepatic manifestations, especially neurologic complications. Progress in the understanding of the biology of HEV should contribute to improved control and treatment of HEV infection.

Characterization and epitope mapping of monoclonal antibodies raised against rat hepatitis E virus capsid protein: An evaluation of their neutralizing activity in a cell culture system

Hepatitis E virus (HEV) is the causative agent of acute hepatitis. Rat HEV is a recently discovered virus related to, but distinct from, human HEV. Since laboratory rats can be reproducibly infected with rat HEV and a cell culture system has been established for rat HEV, this virus may be used as a surrogate virus for human HEV, enabling studies on virus replication and mechanism of infection. However, monoclonal antibodies (MAbs) against rat HEV capsid (ORF2) protein are not available. In this study, 12 murine MAbs were generated against a recombinant ORF2 protein of rat HEV (rRatHEV-ORF2: amino acids 101-644) and were classified into at least six distinct groups by epitope mapping and a cross-reactivity analysis with human HEV ORF2 proteins. Two non-cross-reactive MAbs recognizing the protruding (P) domain detected both non-denatured and denatured rRatHEV-ORF2 protein and efficiently captured cell culture-produced rat HEV particles that had been treated with deoxycholate and trypsin, but not those without prior treatment. In addition, these two MAbs were able to efficiently neutralize replication of cell culture-generated rat HEV particles without lipid membranes (but not those with lipid membranes) in a cell culture system, similar to human HEV.

Production of infectious ferret hepatitis E virus in a human hepatocarcinoma cell line PLC/PRF/5

A strain of ferret hepatitis E virus (HEV), sF4370, isolated from an imported ferret was used to inoculate a human hepatocarcinoma cell line, PLC/PRF/5. The virus genome and capsid protein were detected in the cell culture supernatant. Immunofluorescence microscopy indicated that the capsid protein was located in the cytoplasm. The virus particles were purified from the culture supernatant by sucrose gradient ultracentrifugation. The capsid protein with molecular mass of ∼72 kDa was detected in fractions with density of 1.150-1.162 g/cm(3), and particles of ferret HEV was associated with cell membrane. The virus recovered from the supernatant was serially passaged with PLC/PRF/5 cells and had the ability to infect ferrets by oral inoculation, indicating that the ferret HEV grown in PLC/PRF/5 was infectious. The establishment of ferret HEV cell culture system might be useful to understand the life cycle, mechanism of infection and replication of ferret HEV.

Construction and characterization of an infectious cDNA clone of rat hepatitis E virus

Rat hepatitis E virus (HEV) is related to human HEV and has been detected in wild rats worldwide. Here, the complete genome of rat HEV strain R63/DEU/2009 was cloned downstream of the T7 RNA polymerase promoter and capped genomic RNA generated by in vitro transcription was injected into nude rats. Rat HEV RNA could be detected in serum and faeces of rats injected intrahepatically, but not in those injected intravenously. Rat HEV RNA-positive faecal suspension was intravenously inoculated into nude rats and Wistar rats leading to rat HEV RNA detection in serum and faeces of nude rats, and to seroconversion in Wistar rats. In addition, rat HEV was isolated in PLC/PRF/5 cells from the rat HEV RNA-positive faecal suspension of nude rats and then passaged. The cell culture supernatant was infectious for nude rats. Genome analysis identified nine point mutations of the cell-culture-passaged virus in comparison with the originally cloned rat HEV genome. The results indicated that infectious rat HEV could be generated from the cDNA clone. As rats are widely used and well-characterized laboratory animals, studies on genetically engineered rat HEV may provide novel insights into organ tropism, replication and excretion kinetics as well as immunological changes induced by hepeviruses.

Hepatitis E virus egress depends on the exosomal pathway, with secretory exosomes derived from multivesicular bodies

Our previous studies indicated that hepatitis E virus (HEV) forms membrane-associated particles in the cytoplasm, most likely by budding into intracellular vesicles, and requires the multivesicular body (MVB) pathway to release virus particles, and the released HEV particles with a lipid membrane retain the trans-Golgi network protein 2 on their surface. To examine whether HEV utilizes the exosomal pathway to release the virus particles, we analysed whether the virion release from PLC/PRF/5 cells infected with genotype 3 HEV (strain JE03-1760F) is affected by treatment with bafilomycin A1 or GW4869, or by the introduction of a small interfering RNA (siRNA) against Rab27A or Hrs. The extracellular HEV RNA titre was increased by treatment with bafilomycin A1, but was decreased by treatment with GW4869. The relative levels of virus particles released from cells depleted of Rab27A or Hrs were decreased to 16.1 and 11.5 %, respectively, of that released from cells transfected with negative control siRNA. Electron microscopic observations revealed the presence of membrane-associated virus-like particles with a diameter of approximately 50 nm within the MVB, which possessed internal vesicles in infected cells. Immunoelectron microscopy showed positive immunogold staining for the HEV ORF2 protein on the intraluminal vesicles within the MVB. Additionally, immunofluorescence analysis indicated the triple co-localization of the ORF2, ORF3 and CD63 proteins in the cytoplasm, as specific loculated signals, supporting the presence of membrane-associated HEV particles within the MVB. These findings indicate that membrane-associated HEV particles are released together with internal vesicles through MVBs by the cellular exosomal pathway.