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

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.

Animal Models for Hepatitis E Virus

Animal models are one of the most important tools in the study of human hepatitis E virus (HEV) infection. They are particularly important in light of the major limitations of the cell culture system for HEV. Besides nonhuman primates, which are extremely valuable because of their susceptibility to HEV genotypes 1-4, animals like swine, rabbit, and humanized mice are also potential models for studies of pathogenesis, cross-species infection, and the molecular biology of HEV. Identification of a useful animal model for human HEV infection studies is crucial to further investigations into this ubiquitous yet poorly understood virus and facilitate the development of antiviral therapeutics and vaccines.

Subclinical hepatitis E virus infection in laboratory ferrets in the UK

Ferrets are widely used for experimental modelling of viral infections. However, background disease in ferrets could potentially confound intended experimental interpretation. Here we report the detection of a subclinical infection of ferret hepatitis E virus (FRHEV) within a colony sub-group of female laboratory ferrets that had been enrolled on an experimental viral infection study (non-hepatitis). Lymphoplasmacytic cuffing of periportal spaces was identified on histopathology but was negative for the RNA and antigens of the administered virus. Follow-up viral metagenomic analysis conducted on liver specimens revealed sequences attributed to FRHEV and these were confirmed by reverse-transcriptase polymerase chain reaction. Further genomic analysis revealed contiguous sequences spanning 79–95 % of the FRHEV genome and that the sequences were closely related to those reported previously in Europe. Using in situ hybridization by RNAScope, we confirmed the presence of HEV-specific RNA in hepatocytes. The HEV open reading frame 2 (ORF2) protein was also detected by immunohistochemistry in the hepatocytes and the biliary canaliculi. In conclusion, the results of our study provide evidence of background infection with FRHEV in laboratory ferrets. As this infection can be subclinical, we recommend routine monitoring of ferret populations using virological and liver function tests to avoid incorrect causal attribution of any liver disease detected in in vivo studies.

Identification of Hepatitis E Virus in the Feces of Red Foxes (Vulpes vulpes)

Simple Summary

Orthohepeviruses, commonly known as Hepatitis E virus (HEV), is a diverse virus group belonging to the family of Hepeviridae and is responsible for acute hepatitis in humans worldwide. These viruses show a relatively strict host specificity, e.g., rodent-related, avian-related, or even bat-related virus groups. However, similar (HEV-like) viruses have been identified in carnivores; some of them form a new genetically separated group, while others show a close evolutionary relationship with the rodent-related group, thus makes the strict host-specificity questionable and the classification of these new strains uncertain. Herein, we investigated feces of red foxes, the most widespread carnivore species worldwide, to identify the Hepatitis E virus and to ascertain their evolutionary origin via sequencing. The non-invasively collected fecal samples can provide information about the presence of viruses specific to the host and viruses derived from their prey as well. The virus we detected from our samples showed a very close relationship (91% identity) with rodent-related HEV described before from common voles, whilst a more distant relationship (85%) with fox-specific HEV strains was observed. Our results strongly support “the dietary-origin” of unclassified HEV-like strains described from various predator species.

Abstract

Orthohepeviruses (HEV) can infect a wide range of animals, showing a relatively strict host specificity; however, its zoonotic potential, natural transmission in the wildlife are less known. Several new HEV-like viruses have been identified in various animal species, including carnivores; however, the phylogenetic relationship among these viruses is poorly resolved, since some of them were known as rodent-related so far. The red fox, the most widespread carnivore worldwide, is a known reservoir of several viruses that transmit from wildlife to humans or domestic animals; they might have a defined role in the circulation of rodent-borne HEV. In this study, we performed a HEV survey by heminested RT-PCR (Reverse Transcription PCR) on red fox fecal samples to investigate the presence of HEV in red foxes living in natural conditions, and to explore the origin of the virus via phylogenetic analysis. Out of the 26 investigated samples, HEV RNA was identified in one sample. Following Sanger sequencing, the novel sequence displayed 91% identity on the nucleotide level with recently published European common vole-HEV derived from Microtus arvalis. In contrast, it shared 85% nucleotide similarity with HEV strains described previously in red foxes. Our results strongly support “the dietary-origin” of unclassified HEV-like strains described from predators that usually prey on rodents.

Emerging Zoonotic Diseases in Ferrets

As veterinarians, we may be the first to diagnose emerging zoonotic diseases in ferrets and may be at increased risk of exposure. Pseudomonas luteola is a bacterial infection that causes respiratory disease, panniculitis, sialadenitis, and abscess formation. Hepatitis E virus can cause subclinical infection, acute hepatitis, and persistent infection. Since the 2013 article discussing the 2009 influenza pandemic affecting ferrets, there has been an additional case of suspected anthroponotic infection in a pet ferret and experimental infection with influenza viruses from humans, cats, and dogs.

In vivo models for studying Hepatitis E virus infection; Updates and applications

Hepatitis E virus (HEV) is the most common cause of acute viral hepatitis globally. HEV belongs to the Hepeviridae family and at least five genotypes (gt) infect humans. Several animal species are reservoirs for different HEV strains, and they are the source of infection for humans. Some HEV strains are species specific, but other strains could cross species and infect many hosts. The study of HEV infection and pathogenesis was hampered due to the lack of an in vitro and in vivo robust model system. The cell culture system has been established for certain HEV strains, especially gt3 and 4, but gt1 strains replicate poorly in vitro. To date, animal models are the best tool for studying HEV infection. Non-human primates (NHPs) and pigs are the main animal models used for studying HEV infection, but ethical and financial concerns restrict the use of NHPs in research. Therefore, new small animal models have been developed which help more progress in HEV research. In this review, we give updates on the animal models used for studying HEV infection, focusing on the applicability of each model in studying different HEV infections, cross-species infection, virus-host interaction, evaluation of anti-HEV therapies and testing potential HEV vaccines.

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.

Animal Models for Hepatitis E virus

Hepatitis E virus (HEV) is an underdiagnosed pathogen with approximately 20 million infections each year and currently the most common cause of acute viral hepatitis. HEV was long considered to be confined to developing countries but there is increasing evidence that it is also a medical problem in the Western world. HEV that infects humans belongs to the Orthohepevirus A species of the Hepeviridae family. Novel HEV-like viruses have been observed in a variety of animals and some have been shown to be able to cross the species barrier, causing infection in humans. Several cell culture models for HEV have been established in the past years, but their efficiency is usually relatively low. With the circulation of this virus and related viruses in a variety of species, several different animal models have been developed. In this review, we give an overview of these animal models, indicate their main characteristics, and highlight how they may contribute to our understanding of the basic aspects of the viral life cycle and cross-species infection, the study of pathogenesis, and the evaluation of novel preventative and therapeutic strategies.