Systematic pathogenesis and replication of avian hepatitis E virus in specific-pathogen-free adult chickens

The zoonotic LCK-3110 strain of Rocahepevirus ratti leads to mild infection in chickens after experimental inoculation

Rocahepevirus ratti [rat hepatitis E virus (HEV)] was originally isolated from rats and found to be non-infectious to nonhuman primates, suggesting humans were not a susceptible host. However, in 2018, rat HEV infections were identified in human patients. High seroprevalence for rat HEV in rats in many countries necessitates studying this emerging zoonotic outbreak. Lack of a human derived rat HEV infectious clone, cell culture systems, and animal models have hindered this effort. In response to the increase in human infection cases by rat HEV, we utilized an infectious clone of the zoonotic rat HEV LCK-3110 strain originally reported from human cases. Capped RNA transcripts of the rat HEV LCK-3110 strain were synthesized, and replication was assessed in both cell culture via transfection and chickens via intrahepatic inoculation. Naive chickens were cohoused together with inoculated chickens. Our results demonstrated that although chickens were susceptible, virus replication was inefficient with only a few of the chickens inoculated with rat HEV having low levels of viremia and fecal virus shedding. However, LCK-3110 HEV was able to transmit between chickens as several naive cohoused chickens became infected as evidenced by viremia, fecal shedding, and the presence of viral protein upon histopathology of the liver. Rat HEV is an emerging zoonotic virus with an ability to spillover across species. Chickens have potential to serve as intermediary hosts, possibly playing a role in rat HEV spread and exposure to humans.

Pathogenicity of two different genotypes avian hepatitis E strains in laying hens and silkie fowl

To determine the pathogenicity of two different genotypes of avian hepatitis E strains in two species of birds, a total of thirty healthy 12-week-old birds were used. After inoculation, fecal virus shedding, viremia, seroconversion, serum alanine aminotransferase (ALT) increases and liver lesions were evaluated. The results revealed that CHN-GS-aHEV and CaHEV could both infect Hy-Line hens and silkie fowls, respectively. Compared to the original avian HEV strain, the cross-infected virus exhibited a delay of 2 weeks and 1 week in emerged seroconversion, viremia, fecal virus shedding, and increased ALT level, and also showed mild liver lesions. These findings suggested that CHN-GS-aHEV may have circulated in chickens. Overall, these two different genotypes of avian HEV showed some variant pathogenicity in different bird species. This study provides valuable data for further analysis of the epidemic conditions of two avian HEVs in Hy-Line hens and silkie fowls.

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.

Hepatitis E virus causes apoptosis of ovarian cells in hens and resulting in a decrease in egg production

Previous studies have shown that avian hepatitis E virus (HEV) decreases egg production by 10-40% in laying hens, but have not fully elucidated the mechanism of there. In this study, we evaluated the replication of avian HEV in the ovaries of laying hens and the mechanism underlying the decrease in egg production. Forty 150-days-old commercial laying hens were randomly divided into 2 groups of 20 hens each. A total of 1 mL (104GE) of avian HEV stock was inoculated intravenously into each chicken in the experimental group, with 20 chickens in the other group serving as negative controls. Five chickens from each group were necropsied weekly for histopathological examination. The pathogenicity of avian HEV has been characterized by seroconversion, viremia, fecal virus shedding, ovarian lesions, and decreased egg production. Both positive and negative-strand avian HEV RNA, and ORF2 antigens can be detected in the ovaries, suggesting that avian HEV can replicate in the ovaries and serve as an important extrahepatic replication site. The ovaries of laying hens underwent apoptosis after avian HEV infection. These results indicate that avian HEV infection and replication in ovarian tissues cause structural damage to the cells, leading to decreased egg production.

Animal models of hepatitis E infection: Advances and challenges

Hepatitis E virus (HEV) is one of the leading causes of acute viral hepatitis worldwide. Although most of HEV infections are asymptomatic, some patients will develop the symptoms, especially pregnant women, the elderly, and patients with preexisting liver diseases, who often experience anorexia, nausea, vomiting, malaise, abdominal pain, and jaundice. HEV infection may become chronic in immunosuppressed individuals. In addition, HEV infection can also cause several extrahepatic manifestations. HEV exists in a wide range of hosts in nature and can be transmitted across species. Hence, animals susceptible to HEV can be used as models. The establishment of animal models is of great significance for studying HEV transmission, clinical symptoms, extrahepatic manifestations, and therapeutic strategies, which will help us understand the pathogenesis, prevention, and treatment of hepatitis E. This review summarized the animal models of HEV, including pigs, monkeys, rabbits, mice, rats, and other animals. For each animal species, we provided a concise summary of the HEV genotypes that they can be infected with, the cross-species transmission pathways, as well as their role in studying extrahepatic manifestations, prevention, and treatment of HEV infection. The advantages and disadvantages of these animal models were also emphasized. This review offers new perspectives to enhance the current understanding of the research landscape surrounding HEV animal models.

Animal Models for Studying Congenital Transmission of Hepatitis E Virus

One of the most intriguing issues in the hepatitis E virus (HEV) field is the significant increase in mortality rates of the mother and fetus when infection occurs in the second and third trimesters of gestation. A virus that is normally self-limiting and has a mortality rate of less than one percent in otherwise healthy individuals steeply rises by up to 30% in these pregnant populations. Answering this pivotal question has not been a simple task. HEV, in general, has been a difficult pathogen to understand in the laboratory setting. A historical lack of ability to efficiently propagate the virus in tissue culture models has led to many molecular aspects of the viral lifecycle being understudied. Although great strides have been made in recent years to adapt viruses to cell culture, this field remains behind other viruses that are much easier to replicate efficiently in vitro. Some of the greatest discoveries regarding HEV have come from using animal models for which naturally occurring strains of HEV have been identified, including pigs and chickens, but key limitations have made animal models imperfect for studying all aspects of human HEV infections. In addition to the difficulties working with HEV, pregnancy is a very complicated biological process with an elaborate interplay between many different host systems, including hormones, cardiovascular, kidneys, respiratory, gastrointestinal, epithelial, liver, metabolic, immune, and others. Significant differences between the timing and interplay of these systems are notable between species, and making direct comparisons between animals and humans can be difficult at times. No simple answer exists as to how HEV enhances mortality in pregnant populations. One of the best approaches to studying HEV in pregnancy is likely a combinatorial approach that uses the best combination of emerging in vitro and in vivo systems while accounting for the deficiencies that are present in each model. This review describes many of the current HEV animal model systems and the strengths and weaknesses of each as they apply to HEV pregnancy-associated mortality. We consider factors that are critical to analyzing HEV infection within the host and how, despite no perfect animal model for human pregnancy mortality existing, recent developments in HEV models, both in vitro and in vivo, are advancing our overall understanding of HEV in the pregnant host.

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.

Revisiting the Mongolian Gerbil Model for Hepatitis E Virus by Reverse Genetics

Hepatitis E virus (HEV) is a major cause of acute viral hepatitis in humans. A convenient small mammalian model for basic research and antiviral testing is still greatly needed. Although a small rodent, the Mongolian gerbil, was reported to be susceptible to swine genotype-4 HEV infection, whether the previous results were reliable and consistent needs to be validated by using biologically pure HEV stocks or infectious RNA. In this study, we revisited this gerbil infection model for human HEV of genotype 1, 3, or 4 (G1, G3, or G4) by HEV reverse genetics. Gerbils inoculated intrahepatically with capped G3 HEV RNA transcripts or intraperitoneally with infectious G3 cloned HEV produced robust infection, as evidenced by presence of HEV in livers, spleens, and feces for up to 7 weeks post inoculation, seroconversion, and pathological liver lesions. Furthermore, the value of the gerbil model in antiviral testing and type I IFN in host defense was assessed. We demonstrated the effectiveness of peg-IFNα-2a and ribavirin in inhibiting HEV replication in gerbils. By treatment with two molecule inhibitors of TBK1, we also revealed a role of RIG-I like receptor-interferon regulatory factor 3 in host anti-HEV innate immune sensing in this in vivo model. Finally, susceptibility of G4 HEV was demonstrated in intrahepatically inoculated gerbils with infectious HEV RNA transcripts, whereas no evidence for G1 HEV susceptibility was found. The availability of the convenient gerbil model will greatly facilitate HEV-specific antiviral development and assess the mechanism of host immune response during HEV infection. IMPORTANCE HEV infects >20 million people annually, causing acute viral hepatitis as well as chronic hepatitis, neurological diseases, and pregnancy-associated high mortality, which require therapeutic intervention. The HEV antiviral research is largely limited by the lack of a convenient small animal model. Here we revisit the Mongolian gerbil model for three genotypes of human HEV by infectious HEV clones and recognized standards of experimental procedures. Fecal virus shedding, seroconversion, and pathological liver lesions could be detected in HEV-inoculated gerbils. We demonstrate the effectiveness and usefulness of this model in testing antiviral drugs, and in assessing the mechanism of host innate immune response upon HEV infection. This conventional rodent model will aid in future antiviral development and delineating mechanism of host immune response.

Isolation, identification and genome analysis of an avian hepatitis E virus from white-feathered broilers in China

Avian hepatitis E virus (HEV) is the major causative pathogen of the big liver and spleen disease, hepatitis-splenomegaly syndrome, and hepatic rupture hemorrhage syndrome. Until now, there are 6 different avian HEV genotypes that infect chickens have been reported worldwide. Epidemiologic investigations of the avian HEV demonstrated that avian HEV has been widely spread in China in recent years. In this study, an avian HEV named YT-aHEV was obtained from white-feathered broilers using LMH cells by virus isolation assay in Shandong province, China. The complete genome consists of 6656-nt excluding the poly(A) tail. The isolate was highly similar to the CaHEV strain and segregated into the same branch belonging to avian HEV genotype 3. Indirect immunofluorescence using capsid protein-specific polyclonal antibodies confirmed that YT-aHEV could establish productive infection and replicate stably in LMH cells. Furthermore, an in vivo avian HEV infection model was established successfully in specific pathogen-free chicken embryos by intravenous experiments. In the present study, we demonstrate an avian HEV infection associated with liver lesions of hemorrhage and swelling by LMH cells for the first time in a white-feather broiler flock in China. This research also provides a new diagnosis method for detection of avian HEV, which laid a foundation for the understanding of pathogenicity and molecular biology of this virus for further study.

Genetic diversity of avian hepatitis E virus in China, 2018-2019

Avian hepatitis E virus (HEV) is highly variable and has multiple genotypes. Previous studies showed that the current epidemic strain in China is genotype 5, but the relevant detection was only carried out in flocks with hepatic rupture haemorrhage syndrome, which does not mean that other genotypes do not exist. In this study, a broader analysis involving different chicken flocks was performed to understand the epidemic status of avian HEV in China. The results showed that the HEV-positive rate of all samples was 7.92% (78/985), and four different genotypes have been identified by analysing a truncate capsid gene fragment, while the homology between them is about 80%. Two of them are separately known as genotype 3 and genotype 5, while the other two are completely unidentified, indicating that there are multiple genotypes of avian HEV prevalent in China. At the same time, the distribution of these genotypes has no obvious geographical clustering pattern, only slightly different in commercial layers, broilers and some indigenous species. This study shows the genetic diversity of avian HEV in China and reminds us to pay more attention to its variation and evolution.

Identification and pathogenicity of a novel genotype avian hepatitis E virus from silkie fowl (gallus gallus)

Hepatitis E virus (HEV) is a public health concern because of its zoonotic potential; however, the host species spectrum and the genetic diversity of HEV in many birds are unknown. In the present study, a novel genotype avian HEV was isolated from a bird, silkie fowl, and designated CHN-GS-aHEV (GenBank No. MN562265). The genome of CHN-GS-aHEV was analyzed in comparison with other avian HEVs' and the pathogenicity in silkie fowl was characterized. The results show that the CHN-GS-aHEV shares about 81 % identity with known avian HEV in chickens, ORF3 shares the highest identity (85.1 %-88.0 %) at the nucleotide level, while ORF2 shares the highest identity (96.5 %-98.0 %) at the amino acid level, indicating that the CHN-GS-aHEV belongs to a new genotype avian HEV. The pathogenicity study showed that silkie fowl experimentally infected with the CHN-GS-aHEV demonstrated seroconversion, viremia, fecal virus shedding, liver lesions, and increased ALT level. Furthermore, ultrastructural changes in hepatocyte cells by transmission electron microscopy were characterized by the loss of mitochondrial cristae and swollen mitochondria and endoplasmic reticulum in the infected birds, suggesting that these two organelles may play a significant role in HEV replication. Overall, this study reports the complete genome characterization of a novel avian HEV and successful experimental infection in silkie fowl, and may be serving as a prominent indicator for additional avian HEV detection in other species.

Complete genome analysis of avian hepatitis E virus from chicken with hepatic rupture hemorrhage syndrome

Since 2016, severe outbreaks of hepatic rupture hemorrhage syndrome (HRHS) associated with infections of tentative novel avian hepatitis E virus (HEV) have emerged in chickens in China, causing increased mortality and decreased laying rate in adult hens and disturbing the hatching and breeding of chicks. To further identify the genotype and gain a better understanding of the genetic properties of the avian HEV responsible for that, a strain from Hebei province was isolated, purified and sequenced in this study. Results identified a novel avian HEV genotype, sharing 79.5-86.9% identities with other published avian HEV strains, and having higher identities with Orthohepevirus A HEV strains. More importantly, the new isolate contains various amino-acid substitutions in its functional proteins, including methyltransferase, helicase, RNA-dependent RNA polymerase. The data presented in this report will enhance the current understanding of the genetic diversity of the avian HEV and provide additional insight into the critical factors that determine the pathogenicity.

Co-infection with avian hepatitis E virus and avian leukosis virus subgroup J as the cause of an outbreak of hepatitis and liver hemorrhagic syndromes in a brown layer chicken flock in China

Hens of a commercial Hy-line brown layer flock in China exhibited increased mortality and decreased egg production at 47 wk of age. From 47 to 57 wk, average weekly mortality increased from 0.11 to 3.0%, and egg production decreased from 10 to 30%, with a peak mortality rate (3.0%) observed at 54 wk of age. Necropsy of 11 birds demonstrated tissue damage that included hepatitis, liver hemorrhage, rupture, and/or enlarged livers. Microscopic liver lesions exhibited hepatocytic necrosis, lymphocytic periphlebitis, and myeloid leukosis. While no bacteria were recovered from liver and spleen samples, avian hepatitis E virus (HEV) RNA was detected in all 11 tested hens by nested reverse transcription-polymerase chain reaction. Of these, subgroup J avian leukosis virus (ALV-J) proviral DNA was detected in 5 hens by PCR. Alignments of partial ORF2 gene sequences obtained here demonstrated shared identity (76 to 97%) with corresponding sequences of other known avian HEV isolates. Env sequences of ALV-J isolates obtained here shared 50.1 to 55% identity with other ALV subgroups and 91.8 to 95.5% identity with other known ALV-J isolates. Phylogenetic tree analysis of selected sequences obtained here grouped an avian HEV sequence with genotype 3 HEV and assigned an ALV-J sequence to a branch separate from known ALV-J subgroups. Immunohistochemical results confirmed the presence of avian HEV and ALV-J in livers. Therefore, these results suggest that avian HEV and ALV-J co-infection caused the outbreak of hepatitis and liver hemorrhagic syndrome observed in the layer hen flock analyzed in this study.

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.

CD8+ lymphocytes but not B lymphocytes are required for protection against chronic hepatitis E virus infection in chickens

Hepatitis E is an important global disease, causing outbreaks of acute hepatitis in many developing countries and sporadic cases in industrialized countries. Hepatitis E virus (HEV) infection typically causes self-limiting acute hepatitis but can also progress to chronic disease in immunocompromised individuals. The immune response necessary for the prevention of chronic infection is T cell-dependent; however, the arm of cellular immunity responsible for this protection is not currently known. To investigate the contribution of humoral immunity in control of HEV infection and prevention of chronicity, we experimentally infected 20 wild-type (WT) and 18 immunoglobulin knockout (JH-KO) chickens with a chicken strain of HEV (avian HEV). Four weeks postinfection (wpi) with avian HEV, JH-KO chickens were unable to elicit anti-HEV antibody but had statistically significantly lower liver lesion scores than the WT chickens. At 16 wpi, viral RNA in fecal material and liver, and severe liver lesions were undetectable in both groups. To determine the role of cytotoxic lymphocytes in the prevention of chronicity, we infected 20 WT and 20 cyclosporine and CD8⁺ antibody-treated chickens with the same strain of avian HEV. The CD8 ⁺ lymphocyte-depleted, HEV-infected chickens had higher incidences of prolonged fecal viral shedding and statistically significantly higher liver lesion scores than the untreated, HEV-infected birds at 16 wpi. The results indicate that CD8 ⁺ lymphocytes are required for viral clearance and reduction of liver lesions in HEV infection while antibodies are not necessary for viral clearance but may contribute to the development of liver lesions in acute HEV infection.

Avian Hepatitis E Virus: With the Trend of Genotypes and Host Expansion

Avian hepatitis E virus (HEV) is a single-stranded, positive-sense RNA virus with a complete genome of approximately 6.6 kb in size. To date, four major genotypes of avian HEV have been identified and classified into the Orthohepevirus B genus of the family Hepeviridae. The avian HEV associated with hepatitis-splenomegaly syndrome, big liver and spleen disease or hepatic rupture hemorrhage syndrome in chickens is genetically and antigenically related to mammalian HEV. With the increased genotypes of avian HEV identified, a broader host tropism is also notable in the epidemiological studies. Due to the lack of an efficient cell culture system, the mechanisms of avian HEV replication and pathogenesis are still poorly understood. The recent identification and characterization of animal strains of avian HEV has demonstrated the virus' ability of cross-species infection. Although it has not yet been detected in humans, the potential threat of a zoonotic HEV capable of transmission to humans needs to be taken into consideration. This review article focuses on the current knowledge regarding avian HEV in virology, epidemiology, pathogenesis, clinical presentation, transmission, diagnosis and prevention.

HIGHLIGHTS

- The mechanisms of avian HEV replication and pathogenesis are still poorly understood due to the lack of an efficient cell culture system.- A broader host tropism is also notable in the epidemiological studies with the increased genotypes of avian HEV identified.- The recent identification and characterization of animal strains of avian HEV has demonstrated the virus' ability of cross-species infection.- The potential threat of a zoonotic HEV capable of transmission to humans needs to be taken into consideration.

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.

Chicken Organic Anion-Transporting Polypeptide 1A2, a Novel Avian Hepatitis E Virus (HEV) ORF2-Interacting Protein, Is Involved in Avian HEV Infection

Avian hepatitis E virus (HEV) is the main causative agent of big liver and spleen disease in chickens. Due to the absence of a highly effective cell culture system, there are few reports about the interaction between avian HEV and host cells. In this study, organic anion-transporting polypeptide 1A2 (OATP1A2) from chicken liver cells was identified to interact with ap237, a truncated avian HEV capsid protein spanning amino acids 313 to 549, by a glutathione S-transferase (GST) pulldown assay. GST pulldown and indirect enzyme-linked immunosorbent assays (ELISAs) further confirmed that the extracellular domain of OATP1A2 directly binds with ap237. The expression levels of OATP1A2 in host cells are positively correlated with the amounts of ap237 attachment and virus infection. The distribution of OATP1A2 in different tissues is consistent with avian HEV infection in vivo Finally, when the functions of OATP1A2 in cells are inhibited by its substrates or an inhibitor or blocked by ap237 or anti-OATP1A2 sera, attachment to and infection of host cells by avian HEV are significantly reduced. Collectively, these results displayed for the first time that OATP1A2 interacts with the avian HEV capsid protein and can influence viral infection in host cells. The present study provides new insight to understand the process of avian HEV infection of host cells.IMPORTANCE The process of viral infection is centered around the interaction between the virus and host cells. Due to the lack of a highly effective cell culture system in vitro, there is little understanding about the interaction between avian HEV and its host cells. In this study, a total of seven host proteins were screened in chicken liver cells by a truncated avian HEV capsid protein (ap237) in which the host protein OATP1A2 interacted with ap237. Overexpression of OATP1A2 in the cells can promote ap237 adsorption as well as avian HEV adsorption and infection of the cells. When the function of OATP1A2 in cells was inhibited by substrates or inhibitors, attachment and infection by avian HEV significantly decreased. The distribution of OATP1A2 in different chicken tissues corresponded with that in tissues during avian HEV infection. This is the first finding that OATP1A2 is involved in viral infection of host cells.

Comparative Pathology of Hepatitis A Virus and Hepatitis E Virus Infection

Hepatitis A virus (HAV) and hepatitis E virus (HEV) cause acute, self-limiting hepatic infections that are usually spread by the fecal-oral route in humans. Naturally occurring and experimental infections are possible in a variety of nonhuman primates and, in the case of HEV, a number of other species. Many advances in understanding the pathogenesis of these viruses have come from studies in experimental animals. In general, animals infected with these viruses recapitulate the histologic lesions seen in infected humans, but typically with less severe clinical and histopathological manifestations. This review describes the histopathologic changes associated with HAV and HEV infection in humans and experimental animals.

Epidemiological investigation of the novel genotype avian hepatitis E virus and co-infected immunosuppressive viruses in farms with hepatic rupture haemorrhage syndrome, recently emerged in China

Since 2016, hepatic rupture haemorrhage syndrome (HRHS) appeared in chickens of China and caused huge economic loss. To assess the infection status of the avian hepatitis E virus (HEV) and co-infected viruses, including avian leukosis virus (ALV), reticuloendotheliosis virus (REV), fowl adenovirus (FAdV), and chicken infectious anaemia virus (CIAV), in farms with HRHS, 180 liver samples were collected from 24 farms in different provinces and detected by strict molecular virology methods. Results showed that the positive rates of HEV, ALV, REV, FAdV, and CIAV were 74.44%, 20.00%, 27.78%, 31.11%, and 12.22%, respectively, whereas there are also 112 samples with co-infection, for a rate of 58%. Meanwhile, the positive rate of HEV decreased gradually with age; the lowest positive rate of ALV (5.76%) and REV (19.23%) appeared in 25-35 weeks age, during which the positive rate of CIAV was the highest (19.23%); the positive rate of HEV in layers (64.00%) was lower than that of broilers (83.33%), but the positive rates of ALV (38.46%) and CIAV (15.38%) in layers were higher than that of broilers (5.88%, 9.80%); the positive rates of HEV (75.88%) and CIAV (15.60%) in parental generation (PG) were higher than that of commodity generation (CG, 64.10%, 0.00%), whereas the positive rate of ALV showed inverse relationship (PG: 14.89%; CG: 38.46%). Additionally, phylogenetic analysis showed that all the avian HEV identified this study belong to a novel genotype, and found the close relationship between the wild strains (REV and CIAV) and corresponding isolates from contaminated vaccine. The data presented in this report will enhance the current understanding of the epidemiology characteristics in farms with HRHS in China.

Infection Dynamics of Hepatitis E Virus in Wild-Type and Immunoglobulin Heavy Chain Knockout JH -/- Gnotobiotic Piglets

Hepatitis E virus (HEV), the causative agent of hepatitis E, is an important but incompletely understood pathogen causing high mortality during pregnancy and leading to chronic hepatitis in immunocompromised individuals. The underlying mechanisms leading to hepatic damage remain unknown; however, the humoral immune response is implicated. In this study, immunoglobulin (Ig) heavy chain J_H ^-/- knockout gnotobiotic pigs were generated using CRISPR/Cas9 technology to deplete the B-lymphocyte population, resulting in an inability to generate a humoral immune response to genotype 3 HEV infection. Compared to wild-type gnotobiotic piglets, the frequencies of B lymphocytes in the Ig heavy chain J_H ^-/- knockouts were significantly lower, despite similar levels of other innate and adaptive T-lymphocyte cell populations. The dynamic of acute HEV infection was subsequently determined in heavy chain J_H ^-/- knockout and wild-type gnotobiotic pigs. The data showed that wild-type piglets had higher viral RNA loads in feces and sera compared to the J_H ^-/- knockout pigs, suggesting that the Ig heavy chain J_H ^-/- knockout in pigs actually decreased the level of HEV replication. Both HEV-infected wild-type and J_H ^-/- knockout gnotobiotic piglets developed more pronounced lymphoplasmacytic hepatitis and hepatocellular necrosis lesions than other studies with conventional pigs. The HEV-infected J_H ^-/- knockout pigs also had significantly enlarged livers both grossly and as a ratio of liver/body weight compared to phosphate-buffered saline-inoculated groups. This novel gnotobiotic pig model will aid in future studies into HEV pathogenicity, an aspect which has thus far been difficult to reproduce in the available animal model systems.IMPORTANCE According to the World Health Organization, approximately 20 million HEV infections occur annually, resulting in 3.3 million cases of hepatitis E and >44,000 deaths. The lack of an efficient animal model that can mimic the full-spectrum of infection outcomes hinders our ability to delineate the mechanism of HEV pathogenesis. Here, we successfully generated immunoglobulin heavy chain J_H ^-/- knockout gnotobiotic pigs using CRISPR/Cas9 technology, established a novel J_H ^-/- knockout and wild-type gnotobiotic pig model for HEV, and systematically determined the dynamic of acute HEV infection in gnotobiotic pigs. It was demonstrated that knockout of the Ig heavy chain in pigs decreased the level of HEV replication. Infected wild-type and J_H ^-/- knockout gnotobiotic piglets developed more pronounced HEV-specific lesions than other studies using conventional pigs, and the infected J_H ^-/- knockout pigs had significantly enlarged livers. The availability of this novel model will facilitate future studies of HEV pathogenicity.

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.

Cross-species infection of mice by rabbit hepatitis E virus

Rabbits are recognized as a zoonotic reservoir of hepatitis E virus (HEV) for transmission to humans and other zoonotic reservoirs such as swine. The purpose of this study was to assess the ability of rabbit HEV to cross the species barrier to infect mice and also the usefulness of this animal to study HEV transmission and pathogenesis. In this study, uninfected BALB/c mice were experimentally inoculated with rabbit HEV either via gavage or through contact-exposure with infected mice. Rabbit HEV propagation in mice was evaluated by studying fecal virus shedding, viremia, seroconversion and microscopic liver lesions. Rabbit HEV could be detected in all mice infected by gavage, but only in some contact-exposed mice, with some animals exhibiting fecal virus shedding, seroconversion or viremia (one mouse only). Compared with inoculated mice, anti-rabbit HEV antibody titers and viral copy numbers in fecal and serum samples were lower in contact-exposed mice. Infected mice mainly exhibited phlebitis, hepatocyte swelling and necrosis. Microscopic liver lesion scores for inoculated and contact-exposed infected mice were higher than scores for negative controls. This study therefore demonstrates that rabbit HEV could infect BALB/c mice both though inoculation via gavage and through contact-exposure.

Characterization of the novel genotype avian hepatitis E viruses from outbreaks of hepatic rupture haemorrhage syndrome in different geographical regions of China

Since 2016, hepatic rupture haemorrhage syndrome (HRHS) has emerged in layer and broiler breeder hens in several provinces of China, and novel genotype avian hepatitis E viruses were detected from these chickens. To gain a better understanding of the genetic properties of the novel avian HEV strain, the capsid gene of four isolates from birds at four farms experiencing HRHS in different geographical regions were determined and compared with those of reported pathogenic and nonpathogenic avian HEV isolates as well as mammalian HEVs. Results showed that all those isolates share 80.1%-88.2% nucleotide sequence identity and 89.3%-91.9% amino acid sequence identity with other published avian HEV strains, while phylogenetic analysis further demonstrate that a novel genotype avian HEV was epidemic in China. Meanwhile, sequence analysis revealed that those novel isolates contain various amino acid mutations and even a hypervariable region in their major antigenic domains, which might be the critical factors for the pathogenicity elevation and even change their antigenicity. The data presented in this report will enhance the current understanding of the epidemiology and genetic diversity of the novel genotype avian HEV in China and provide additional insight into the critical factors that determine the pathogenicity of it.

Hepatic rupture hemorrhage syndrome in chickens caused by a novel genotype avian hepatitis E virus

Since 2016, severe outbreaks of hepatic rupture hemorrhage syndrome (HRHS) have emerged in chickens in several Chinese provinces and caused huge economic losses to the poultry industry, but the etiological characteristics and pathogenic potential of it has remained unclear. This study sequenced the partial helicase and capsid gene of the potentially novel avian hepatitis E virus (HEV) isolated from chickens with HRHS and tested the pathogenicity of it on SPF chicks, while the appearance of clinical signs, histopathological changes, viral distribution, viremia and viral shedding were monitored for 14 days post-infection (dpi). Analysis revealed that the HRHS related avian HEV belongs to a novel genotype, and infected chicks developed the typical symptoms of HRHS. Thus, this study successfully developed an experimental infection model for studying the pathogenicity and role of the novel avian HEV in HRHS. Meanwhile, the novel avian HEV mainly existed in the liver and spleen, inducing a rapid viremia and chronic viral shedding in infected chicks, and could cause 40% mortality before 14 dpi. In conclusion, this study found the novel genotype avian HEV and confirmed its role in HRHS.

Causes of Normal Mortality in Commercial Egg-Laying Chickens

In a large population of animals, it is normal to have some die each day from causes not related to disease, which is often referred to as natural causes. In poultry production, this phenomenon is commonly referred to as daily mortality. In egg-producing chickens, many of the natural causes of death are associated with making an egg. The causes of normal mortality in commercial egg-laying chicken flocks have been described very little to date. A commercial chicken egg farm, housing approximately two million single-comb white leghorn chickens (Gallus gallus domesticus) in 16 egg-producing flocks, was visited on a monthly basis to monitor bird health, body conditioning, skeletal integrity, and causes of daily mortality in an attempt to provide early detection of health abnormalities. A representative sample of daily mortality from each flock was necropsied to determine the cause of death. Reported herein is a summary of visits for a period of 38 mo from June 2011 to July 2014. The top 15 causes of normal mortality, in rank order of prevalence, were determined to be the following: egg yolk peritonitis, hypocalcemia, gout, self-induced molt, salpingitis, caught by spur, intussusception or volvulus (twisted intestine), cannibalism (pick out), tracheal plug, septicemia, fatty liver syndrome, internal layer, layer hepatitis, persecution, and prolapsed vent. Other causes noted were hyperthermia (during summer), trauma, coccidiosis, ovarian neoplasia, being egg bound, urolithiasis, peritonitis (not egg yolk induced), leg fracture, caught in the structure, tumor (other than ovarian origin), wing fracture, exsanguination, and cardiomyopathy.

Laboratory challenges in the diagnosis of hepatitis E virus

Hepatitis E virus (HEV) is an RNA virus that is an important cause of both acute and chronic hepatitis worldwide. To date, there are eight HEV genotypes that can infect mammals. HEV-1 and HEV-2 infect exclusively humans, while HEV-3 and HEV-4 infect humans and various animals, mainly pigs and deer. Additionally, two new genotypes (HEV-5 and HEV-6) infect mainly wild boar. Recently, newly discovered genotypes HEV-7 and HEV-8 were found to infect camels and possibly humans. Nevertheless, the epidemiological distribution of HEV-7 is not well established. HEV-8 is another newly discovered genotype that was identified in 2016 in Chinese Bactrian camels. Although faecal-oral transmission is the most common route of HEV transmission, HEV can be vertically transmitted from infected mothers to their fetuses. HEV may also spread by zoonotic transmission from infected animals to humans and through person-to-person contact. Nowadays, since the number of reported cases linked to blood donations is increasing annually, HEV is recognized as a transfusion-transmitted virus. Laboratory diagnostic techniques vary in their specificity and sensitivity for HEV detection. Direct techniques allow for detection of the viral proteins, antigens and viral nucleic acid, while HEV-specific IgG and IgM antibodies can help establish a diagnosis in acute and chronic infections. In this review, we will discuss recent technologies in the laboratory diagnosis of HEV, including serological and molecular methods to assess the specificity and sensitivity of currently available HEV commercial assays.

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 chicken are also potential models for studies of pathogenesis, cross-species infection, and the molecular biology of HEV. Identification of the most useful animal model for human HEV infection studies is crucial to further investigations into this ubiquitous yet poorly understood virus.

Effect of housing arrangement on fecal-oral transmission of avian hepatitis E virus in chicken flocks

BACKGROUND

Avian hepatitis E virus (HEV) infection is common in chicken flocks in China, as currently no measures exist to prevent the spread of the disease. In this study, we analyzed the effect of caged versus cage-free housing arrangements on avian HEV transmission. First, 127 serum and 110 clinical fecal samples were collected from 4 chicken flocks including the two arrangements in Shaanxi Province, China and tested for HEV antibodies and/or virus. Concurrently, 36 specific-pathogen-free chickens were divided equally into four experimental living arrangement groups, designated cage-free (Inoculated), caged (Inoculated), cage-free (Negative) and caged (Negative) groups. In caged groups, three cages contained 3 chickens each. Three chickens each from cage-free (Inoculated) and caged (Inoculated) groups (one chicken of each cage) were inoculated by cutaneous ulnar vein with the same dose of avian HEV, respectively. The cage-free (Negative) and caged (Negative) groups served as negative control. Serum and fecal samples were collected at 1 to 7 weeks post-inoculation (wpi) and liver lesions were scored at 7 wpi.

RESULTS

The results of serology showed that the avian HEV infection rate (54.10%) of the cage-free chickens was significantly higher than the one (12.12%) for caged chickens (P < 0.05). Also, the rate of detection of avian HEV RNA in the clinical fecal samples was significantly higher in the cage-free (22.80%, 13/57) than caged birds (5.66%, 3/53). Moreover, under experimental conditions, the infected number of uninoculated cage-free chickens (6) was significantly higher than the one for the uninoculated caged birds (2), as evidenced by seroconversion, fecal virus shedding, viremia and gross and microscopic liver lesions.

CONCLUSIONS

These results suggest that reduction of contact with feces as seen in the caged arrangement of housing chickens can reduce avian HEV transmission. This study provides insights for prevention and control of avian HEV infection in chicken flocks.

Hepatitis Virus Infections in Poultry

Viral hepatitis in poultry is a complex disease syndrome caused by several viruses belonging to different families including avian hepatitis E virus (HEV), duck hepatitis B virus (DHBV), duck hepatitis A virus (DHAV-1, -2, -3), duck hepatitis virus Types 2 and 3, fowl adenoviruses (FAdV), and turkey hepatitis virus (THV). While these hepatitis viruses share the same target organ, the liver, they each possess unique clinical and biological features. In this article, we aim to review the common and unique features of major poultry hepatitis viruses in an effort to identify the knowledge gaps and aid the prevention and control of poultry viral hepatitis. Avian HEV is an Orthohepevirus B in the family Hepeviridae that naturally infects chickens and consists of three distinct genotypes worldwide. Avian HEV is associated with hepatitis-splenomegaly syndrome or big liver and spleen disease in chickens, although the majority of the infected birds are subclinical. Avihepadnaviruses in the family of Hepadnaviridae have been isolated from ducks, snow geese, white storks, grey herons, cranes, and parrots. DHBV evolved with the host as a noncytopathic form without clinical signs and rarely progressed to chronicity. The outcome for DHBV infection varies by the host's ability to elicit an immune response and is dose and age dependent in ducks, thus mimicking the pathogenesis of human hepatitis B virus (HBV) infections and providing an excellent animal model for human HBV. DHAV is a picornavirus that causes a highly contagious virus infection in ducks with up to 100% flock mortality in ducklings under 6 wk of age, while older birds remain unaffected. The high morbidity and mortality has an economic impact on intensive duck production farming. Duck hepatitis virus Types 2 and 3 are astroviruses in the family of Astroviridae with similarity phylogenetically to turkey astroviruses, implicating the potential for cross-species infections between strains. Duck astrovirus (DAstV) causes acute, fatal infections in ducklings with a rapid decline within 1-2 hr and clinical and pathologic signs virtually indistinguishable from DHAV. DAstV-1 has only been recognized in the United Kingdom and recently in China, while DAstV-2 has been reported in ducks in the United States. FAdV, the causative agent of inclusion body hepatitis, is a Group I avian adenovirus in the genus Aviadenovirus. The affected birds have a swollen, friable, and discolored liver, sometimes with necrotic or hemorrhagic foci. Histologic lesions include multifocal necrosis of hepatocytes and acute hepatitis with intranuclear inclusion bodies in the nuclei of the hepatocytes. THV is a picornavirus that is likely the causative agent of turkey viral hepatitis. Currently there are more questions than answers about THV, and the pathogenesis and clinical impacts remain largely unknown. Future research in viral hepatic diseases of poultry is warranted to develop specific diagnostic assays, identify suitable cell culture systems for virus propagation, and develop effective vaccines.

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.

Necrotizing and haemorrhagic hepatitis and enteritis in commercial layer pullets

This case report describes an episode of recurring severe necrotizing and haemorrhagic hepatitis and enteritis experienced in a flock of commercial layer pullets at 12 weeks of age and again at 18 weeks of age in Indiana. Pullets had been vaccinated at 10 weeks old using a trivalent Salmonella Enteritidis (SE)/Newcastle disease/infectious bronchitis oil-emulsion-inactivated vaccine. The pullets were found dead at 12 weeks with firm but friable, enlarged, haemorrhagic livers, enlarged spleens, and necrohaemorrhagic intestines. Histopathologic findings were consistent with a necrotizing and haemorrhagic enteritis and hepatitis. Livers had multiple intra-sinusoidal thrombi, intestines contained Gram-positive bacterial colonies, and spleens had marked lymphoid depletion. The pullets seemed to improve after antibiotic treatment. Pullets were vaccinated with an inactivated SE vaccine at 14 weeks of age. A second spike of mortality occurred at 18 weeks of age. Although clostridial enteritis and hepatitis were highly suspected in the two cases based on macroscopic and microscopic findings, no significant bacterial or viral agents were isolated from the livers and intestines. In summary, lesions in the liver and intestines are speculated to be due to repetitive vaccination, leading to an anamnestic response by the immune system, and resulting in an immune-mediated response. However, much of the pathogenesis is still unclear, and other causes such as unidentified infectious aetiology, transmissible amyloidosis, and hypersensitivity may need further investigation.

Seroprevalence of avian hepatitis E virus and avian leucosis virus subgroup J in chicken flocks with hepatitis syndrome, China

Background

From 2014 to 2015 in China, many broiler breeder and layer hen flocks exhibited a decrease in egg production and some chickens developed hepatitis syndrome including hepatomegaly, hepatic necrosis and hemorrhage. Avian hepatitis E virus (HEV) and avian leucosis virus subgroup J (ALV-J) both cause decreasing in egg production, hepatomegaly and hepatic hemorrhage in broiler breeder and layer hens. In the study, the seroprevalence of avian HEV and ALV-J in these flocks emerging the disease from Shandong and Shaanxi provinces were investigated.

Results

A total of 1995 serum samples were collected from 14 flocks with hepatitis syndrome in Shandong and Shaanxi provinces, China. Antibodies against avian HEV and ALV-J in these serum samples were detected using iELISAs. The seroprevalence of anti-avian HEV antibodies (35.09%) was significantly higher than that of anti-ALV-J antibodies (2.16%) (p = 0.00). Moreover, the 43 serum samples positive for anti-ALV-J antibodies were all also positive for anti-avian HEV antibodies. In a comparison of both provinces, Shandong chickens exhibited a significantly higher seroprevalence of anti-avian HEV antibodies (42.16%) than Shaanxi chickens (26%) (p = 0.00). In addition, the detection of avian HEV RNA and ALV-J cDNA in the liver samples from the flocks of two provinces also showed the same results of the seroprevalence.

Conclusions

In the present study, the results showed that avian HEV infection is widely prevalent and ALV-J infection is endemic in the flocks with hepatitis syndrome from Shandong and Shaanxi provinces of China. These results suggested that avian HEV infection may be the major cause of increased egg drop and hepatitis syndrome observed during the last 2 years in China. These results should be useful to guide development of prevention and control measures to control the diseases within chicken flocks in China.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0892-4) contains supplementary material, which is available to authorized users.

A novel avian-like hepatitis E virus in wild aquatic bird, little egret (Egretta garzetta), in Hungary

Hepatitis E virus (HEV), family Hepeviridae, has public health concerns because of its zoonotic potential; however, the host species spectrum, animal to animal transmissions, the natural chain of hepevirus infections and the genetic diversity of HEV in wildlife especially in birds are less known. Using random amplification and next generation sequencing technology a genetically divergent avian HEV was serendipitously identified in wild bird in Hungary. HEV RNA was detected with high faecal viral load (1.33×10⁸genomiccopies/ml) measured by real-time PCR in faecal sample from a little egret (Egretta garzetta). The complete genome of HEV strain little egret/kocsag02/2014/HUN (KX589065) is 6660-nt long including a 18-nt 5' end and a 103-nt 3' end (excluding the poly(A)-tail). Sequence analyses indicated that the ORF1 (4554nt/1517aa), ORF2 (1728nt/593aa) and ORF3 (339nt/112aa) encoded proteins of little egret/kocsag02/2014/HUN shared the highest identity (62.8%, 71% and 61.5%) to the corresponding proteins of genotype 1 avian (chicken) HEV in species Orthohepevirus B, respectively. This study reports the identification and complete genome characterization of a novel orthohepevirus distantly related to avian (chicken) HEVs at the first time in wild bird. It is important to recognize all potential hosts, reservoirs and spreaders in nature and to reconstruct the phylogenetic history of hepeviruses. Birds could be an important reservoir of HEV generally and could be infected with genetically highly divergent strains of HEV.

Zoonotic Hepatitis E Virus: Classification, Animal Reservoirs and Transmission Routes

During the past ten years, several new hepatitis E viruses (HEVs) have been identified in various animal species. In parallel, the number of reports of autochthonous hepatitis E in Western countries has increased as well, raising the question of what role these possible animal reservoirs play in human infections. The aim of this review is to present the recent discoveries of animal HEVs and their classification within the Hepeviridae family, their zoonotic and species barrier crossing potential, and possible use as models to study hepatitis E pathogenesis. Lastly, this review describes the transmission pathways identified from animal sources.

Swine and rabbits are the main reservoirs of hepatitis E virus in China: detection of HEV RNA in feces of farmed and wild animals

Hepatitis E virus (HEV) infection is recognized as a zoonosis. The prevalence of HEV RNA and anti-HEV antibodies in many animal species has been reported, but the host range of HEV is unclear. The aims of this study were to investigate HEV infection in various animal species and to determine the reservoirs of HEV. Eight hundred twenty-two fecal samples from 17 mammal species and 67 fecal samples from 24 avian species were collected in China and tested for HEV RNA by RT-nPCR. The products of PCR were sequenced and analyzed phylogenetically. The positive rates of HEV RNA isolated from pigs in Beijing, Shandong, and Henan were 33%, 30%, and 92%, respectively, and that from rabbits in Beijing was 5%. HEV RNA was not detectable in farmed foxes, sheep or sika deer, or in wild animals in zoos, including wild boars, yaks, camels, Asiatic black bears, African lions, red pandas, civets, wolves, jackals and primates. Sequence analysis revealed that swine isolates had 97.8%-98.4% nucleotide sequence identity to genotype 4d isolates from patients in Shandong and Jiangsu of China. Phylogenetic analysis showed that swine HEV isolates belong to genotype 4, including subgenotype 4h in Henan and 4d in Beijing and Shandong. The rabbit HEV strains shared 93%-99% nucleotide sequence identity with rabbit strains isolated from Inner Mongolia. In conclusion, swine and rabbits have been confirmed to be the main reservoirs of HEV in China.

Detection of Hepatitis E Virus Antibodies in Dogs in the United Kingdom

Hepatitis E virus (HEV) genotypes 3 and 4 are zoonotic pathogens, with pigs predominantly implicated in disease transmission. The rapid rise in human cases in developed countries over the past decade indicates a change in epidemiology of HEV, and it has been suggested that additional animal species may be involved in transmission of infection. Multiple studies have identified contact with dogs as a risk factor for HEV infection in industrialised nations, and a low seroprevalence to HEV has previously been reported in dogs in low-income countries. In this study we aimed to evaluate the possibility that dogs are susceptible to HEV, and determine the frequency with which this occurs. Serum samples from UK dogs with and without hepatitis were screened for HEV-specific antibodies, and canine liver and stool samples were analysed by qPCR for the presence of HEV RNA. We describe evidence to show HEV infection occurs at low levels in dogs in the UK, but the strain of origin is undetermined. The low seroprevalence level of HEV in dogs implies the risk of zoonotic disease transmission is likely to be limited, but further investigations will be required to determine if HEV-infected dogs can transmit HEV to man.

Hepatitis E Virus and Related Viruses in Animals

Hepatitis E is an acute human liver disease in healthy individuals which may eventually become chronic. It is caused by the hepatitis E virus (HEV) and can have a zoonotic origin. Nearly 57,000 people die yearly from hepatitis E-related conditions. The disease is endemic in both developing and developed countries with distinct epidemiologic profiles. In developing countries, the disease is associated with inadequate water treatment, while in developed countries, transmission is associated with animal contact and the ingestion of raw or uncooked meat, especially liver. All human HEV are grouped into at least four genotypes, while HEV or HEV-related viruses have been identified in an increasing number of domestic and wild animal species. Despite a high genetic diversity, only one single HEV serotype has been described to date for HEV genotypes 1-4. The discovery of new HEV or HEV-related viruses leads to a continuing increase in the number of genotypes. In addition, the genome organization of all these viruses is variable with overlapping open reading frames (ORF) and differences in the location of ORF3. In spite of the role of some domestic and wild animals as reservoir, the origin of HEV and HEV-related viruses in humans and animals is still unclear. This review discusses aspects of the detection, molecular virology, zoonotic transmission and origin of HEV and HEV-related viruses in the context of 'One Health' and establishes a link between the previous and the new taxonomy of this growing virus family.

Naturally occurring animal models of human hepatitis E virus infection

Hepatitis E virus (HEV) is a single-stranded, positive-sense RNA virus in the family Hepeviridae. Hepatitis E caused by HEV is a clinically important global disease. There are currently four well-characterized genotypes of HEV in mammalian species, although numerous novel strains of HEV likely belonging to either new genotypes or species have recently been identified from several other animal species. HEV genotypes 1 and 2 are limited to infection in humans, whereas genotypes 3 and 4 infect an expanding host range of animal species and are zoonotic to humans. Historical animal models include various species of nonhuman primates, which have been indispensable for the discovery of human HEV and for understanding its pathogenesis and course of infection. With the genetic identification and characterization of animal strains of HEV, a number of naturally occurring animal models such as swine, chicken, and rabbit have recently been developed for various aspects of HEV research, including vaccine trials, pathogenicity, cross-species infection, mechanism of virus replication, and molecular biology studies. Unfortunately, the current available animal models for HEV are still inadequate for certain aspects of HEV research. For instance, an animal model is still lacking to study the underlying mechanism of severe and fulminant hepatitis E during pregnancy. Also, an animal model that can mimic chronic HEV infection is critically needed to study the mechanism leading to chronicity in immunocompromised individuals. Genetic identification of additional novel animal strains of HEV may lead to the development of better naturally occurring animal models for HEV. This article reviews the current understanding of animal models of HEV infection in both natural and experimental infection settings and identifies key research needs and limitations.

Construction of an infectious cDNA clone of genotype 1 avian hepatitis E virus: characterization of its pathogenicity in broiler breeders and demonstration of its utility in studying the role of the hypervariable region in virus replication

A full-length infectious cDNA clone of the genotype 1 Korean avian hepatitis E virus (avian HEV) (pT11-aHEV-K) was constructed and its infectivity and pathogenicity were investigated in leghorn male hepatoma (LMH) chicken cells and broiler breeders. We demonstrated that capped RNA transcripts from the pT11-aHEV-K clone were translation competent when transfected into LMH cells and infectious when injected intrahepatically into the livers of chickens. Gross and microscopic pathological lesions underpinned the avian HEV infection and helped characterize its pathogenicity in broiler breeder chickens. The avian HEV genome contains a hypervariable region (HVR) in ORF1. To demonstrate the utility of the avian HEV infectious clone, several mutants with various deletions in and beyond the known HVR were derived from the pT11-aHEV-K clone. The HVR-deletion mutants were replication competent in LMH cells, although the deletion mutants extending beyond the known HVR were non-viable. By using the pT11-aHEV-K infectious clone as the backbone, an avian HEV luciferase reporter replicon and HVR-deletion mutant replicons were also generated. The luciferase assay results of the reporter replicon and its mutants support the data obtained from the infectious clone and its derived mutants. To further determine the effect of HVR deletion on virus replication, the capped RNA transcripts from the wild-type pT11-aHEV-K clone and its mutants were injected intrahepatically into chickens. The HVR-deletion mutants that were translation competent in LMH cells displayed in chickens an attenuation phenotype of avian HEV infectivity, suggesting that the avian HEV HVR is important in modulating the virus infectivity and pathogenicity.

Hepeviridae: an expanding family of vertebrate viruses

The hepatitis E virus (HEV) was first identified in 1990, although hepatitis E-like diseases in humans have been recorded for a long time dating back to the 18th century. The HEV genotypes 1-4 have been subsequently detected in human hepatitis E cases with different geographical distribution and different modes of transmission. Genotypes 3 and 4 have been identified in parallel in pigs, wild boars and other animal species and their zoonotic potential has been confirmed. Until 2010, these genotypes along with avian HEV strains infecting chicken were the only known representatives of the family Hepeviridae. Thereafter, additional HEV-related viruses have been detected in wild boars, distinct HEV-like viruses were identified in rats, rabbit, ferret, mink, fox, bats and moose, and a distantly related agent was described from closely related salmonid fish. This review summarizes the characteristics of the so far known HEV-like viruses, their phylogenetic relationship, host association and proposed involvement in diseases. Based on the reviewed knowledge, a suggestion for a new taxonomic grouping scheme of the viruses within the family Hepeviridae is presented.

Detection and localization of rabbit hepatitis e virus and antigen in systemic tissues from experimentally intraperitoneally infected rabbits

Rabbit hepatitis E virus (HEV) is a novel genotype of HEV, and is considered to pose a risk of zoonotic transmission. Research into the systemic distribution of rabbit HEV in rabbits during different periods of infection has rarely been reported. To better understand this virus, we infected rabbits with second-passage rabbit HEV via an intraperitoneal route. After inoculation, the infection showed two types, temporary and constant infection. The detection of HEV RNA in the feces varied with time, and serum antigen correlated with fecal HEV RNA. Viremia only appeared 72 days after inoculation. The rabbits remained antibody negative throughout the experimental period. When HEV was localized, several organs besides the liver were HEV RNA positive. Tissue antigen was observed immunohistochemically in the different cells of various organs, especially in parts of the small intestine and the characteristic rabbit gut-associated lymphoid tissue. These data provide valuable information for future research into the pathogenesis of HEV.

Antiviral strategies for hepatitis E virus

The hepatitis E virus is a common cause of acute hepatitis. Contrary to hepatitis B and C, hepatitis E is mostly a mild infection, although it has a high mortality in pregnant women and can evolve to chronicity in immunocompromised patients. Ribavirin and pegylated interferon-α are the only available therapies, but both have side effects that are not acceptable for prophylaxis or treatment of mild infections. In addition, these drugs cannot be used for all patient types (e.g. in case of pregnancy, specific organ transplants or co-morbidities) and in resource-poor settings. Hence there is an urgent need for better antiviral treatments that are efficacious and safe, also during pregnancy. In this review, a concise introduction to the virus and disease is provided, followed by a discussion of the available assay systems and potential molecular targets (viral proteins and host factors) for the development of inhibitors of HEV replication. Finally, directions for future research are presented.