Experimental infection of Balb/c nude mice with Hepatitis E virus

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.

Establishment of a robust rat hepatitis E virus fecal-oral infection model and validation for antiviral studies

The hepatitis E virus (HEV) is a major cause of hepatitis, with an estimated 3.3 million symptomatic cases annually. There is no HEV-specific treatment besides the off-label use of ribavirin and a vaccine is only available in China and Pakistan. To aid the development of therapeutic and preventive strategies, there is a need for convenient HEV infection models in small laboratory animals. To this end, we make use of the rat hepatitis E virus. Human infections with this virus have been reported in recent years, making it a relevant pathogen for the establishment of a small animal infection model. We here report that oral gavage of a feces suspension, containing a pre-defined viral RNA load, results in a reproducible synchronized infection in athymic nude rats. This route of administration mimics fecal-oral transmission in a standardized fashion. The suitability of the model to study the effect of antiviral drugs was assessed by using ribavirin, which significantly reduced viral loads in the feces, liver, and other tissues.

Hepatitis E Virus Immunopathogenesis

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

Mitochondrial dysfunction and mitophagy pathway activation in hepatitis E virus-infected livers of Mongolian gerbils

Recently, hepatitis E virus (HEV) has caused large outbreaks and presented a significant public health problem. Thus, the mechanism of HEV has attracted increasing research attention. Previous studies revealed that HEV infection induced hepatocyte injuries and structural and functional changes in mitochondria. These pathological changes affected the life cycle of hepatocytes. However, the precise underlying mechanism and the effector protein responsible for this process remain unclear. In the present study, mitochondrial function and the expression of mitophagy-associated mRNA transcripts and proteins were detected in an HEV- infected Mongolian gerbil model. Observation of ultrastructural changes in the liver of the inoculated group revealed the disappearance of mitochondrial cristae of mitochondrion, blurring of the bilayer structure and cavitation in the cytoplasm. The results showed that the mitochondrial transmembrane potential of decreased, mitochondrial transition pore (MPTP) opening increased, reactive oxygen species (ROS) production increased, and glutathione peroxidase (GSH-Px) activity decreased in the HEV-inoculated group. Moreover, the LC3, Beclin1, BNIP3L, Parkin, PINK1 and P62 mRNA levels were significantly increased (p < 0.05 and p < 0.01) in the inoculated group. Western blot and immunohistochemistry assay analyses detected the upregulation of the mitophagy-associated proteins LC3, Beclin1, BNIP3L, Parkin, PINK1 and P62 (p < 0.05 and p < 0.01) in HEV-infected gerbils. All these data demonstrated that HEV infection in vivo induced mitochondrial dysfunction and the activation of the mitophagy pathway, which might be one of the key factors in hepatocyte injury.

Model systems for studying extrahepatic pathogenesis of hepatitis E virus. Current knowledge and future directions

Hepatitis E Virus is the most common cause of acute viral hepatitis globally. HEV infection is endemic in developing countries. Also, autochthonous and sporadic cases are reported in developed countries. HEV causes acute and chronic infections. Besides, extrahepatic manifestations including neurological, renal, haematological, acute pancreatitis and complications during pregnancy are associated with HEV infections. The pathogenesis of HEV in the extrahepatic tissues is either due to direct cytopathic effect mediated by the virus replication, or immunological mechanisms caused by an uncontrollable host response. Researchers have used different in vivo and in vitro models to study the pathogenesis of HEV in the extrahepatic tissues and analyse the host immune response against HEV infection. This review highlights the extrahepatic disorders associated with HEV infection. We focused on the in vivo and in vitro models as a tool for elucidating the HEV infection beyond the liver and studying the mechanisms of HEV induced tissue damages.

Viral Hepatitis E and Chronicity: A Growing Public Health Concern

Hepatitis E viral infection recently emerges as a global health concern. Over the last decade, the understanding of hepatitis E virus (HEV) had changed with the discovery of new genotypes like genotype-7 and genotype-8 with associated host and mode of infection. Diversification in the mode of hepatitis E infection transmission through blood transfusion, and organ transplants in contrast to classical feco-oral and zoonotic mode is the recent medical concern. The wide spectrum of infection ranging from self-limiting to acute liver failure is now overpowered by HEV genotype-specific chronic infection especially in transplant patients. This concern is further escalated by the extra-hepatic manifestations of HEV targeting the central nervous system (CNS), kidney, heart, and pancreas. However, with the development of advanced efficient cell culture systems and animal models simulating the infection, much clarity toward understanding the pathogenetic mechanism of HEV has been developed. Also this facilitates the development of vaccines research or therapeutics. In this review, we highlight all the novel findings in every aspect of HEV with special emphasis on recently emerging chronic mode of infection with specific diagnosis and treatment regime with an optimistic hope to help virologists and/or liver specialists working in the field of viral hepatitis.

BALB/c Mouse Is a Potential Animal Model System for Studying Acute and Chronic Genotype 4 Hepatitis E Virus Infection

Hepatitis E virus (HEV) is the main pathogen of hepatitis worldwide. However, its infection biology and pathogenesis remain largely unknown. Suitable small-animal models are required to advance the study of HEV infection. Although an efficient model of genotype 1 (gt1) and gt3 HEV infection has been established in human liver chimeric mice, the infectivity of gt4 HEV infection in mice has not been comprehensively characterized. In this study, immunocompromised BALB/c nude, immunocompetent BALB/c, and C57BL/6 mice were inoculated with either gt3 or gt4 HEV (19 HEV strains, including human, swine, macaque-adapted, and cow HEV strains). Infectivity was identified by viral RNA and antigen detection, inflammation, and histopathological analysis. Then, HEV-infected BALB/c mice were treated with antiviral drugs. Acute HEV infection was established in BALB/c mice inoculated with eight gt4 HEV strains. However, gt3 HEV strains failed to achieve active HEV infection. HEV infection was established in BALB/c nude and regular mice inoculated with gt4 HEV but not in C57BL/6 mice. Gt4 HEV infection resulted in rapid viremia and high titers in feces, sera, and replication sites. HEV infection in mice showed no gender preference. Furthermore, chronic gt4 HEV infection was well imitated in BALB/c mice for 32 weeks and caused liver fibrosis.

CONCLUSION

BALB/c mice have a great potential for reproducing the process of gt4 HEV infection. The successful establishment of a gt4 HEV small-animal model provides an opportunity to further understand HEV infection biology and zoonotic transmission and develop anti-HEV vaccine.

Viral delivery of tissue nonspecific alkaline phosphatase diminishes craniosynostosis in one of two FGFR2C342Y/+ mouse models of Crouzon syndrome

Craniosynostosis is the premature fusion of cranial bones. The goal of this study was to determine if delivery of recombinant tissue nonspecific alkaline phosphatase (TNAP) could prevent or diminish the severity of craniosynostosis in a C57BL/6 FGFR2^C342Y/+ model of neonatal onset craniosynostosis or a BALB/c FGFR2^C342Y/+ model of postnatal onset craniosynostosis. Mice were injected with a lentivirus encoding a mineral targeted form of TNAP immediately after birth. Cranial bone fusion as well as cranial bone volume, mineral content and density were assessed by micro CT. Craniofacial shape was measured with calipers. Alkaline phosphatase, alanine amino transferase (ALT) and aspartate amino transferase (AST) activity levels were measured in serum. Neonatal delivery of TNAP diminished craniosynostosis severity from 94% suture obliteration in vehicle treated mice to 67% suture obliteration in treated mice, p<0.02) and the incidence of malocclusion from 82.4% to 34.7% (p<0.03), with no effect on cranial bone in C57BL/6 FGFR2^C342Y/+ mice. In contrast, treatment with TNAP increased cranial bone volume (p< 0.01), density (p< 0.01) and mineral content (p< 0.01) as compared to vehicle treated controls, but had no effect on craniosynostosis or malocclusion in BALB/c FGFR2^C342Y/+ mice. These results indicate that postnatal recombinant TNAP enzyme therapy diminishes craniosynostosis severity in the C57BL/6 FGFR2^C342Y/+ neonatal onset mouse model of Crouzon syndrome, and that effects of exogenous TNAP are genetic background dependent.

Swine hepatitis E virus: Cross-species infection, pork safety and chronic infection

Swine hepatitis E virus (swine HEV) belongs to the species Orthohepevirus A within the genus Orthohepevirus in the family Hepeviridae. Four different genotypes of swine HEV within the species Orthohepevirus A have been identified so far from domesticated and wild swine population: genotypes 3 (HEV-3) and 4 (HEV-4) swine HEVs are zoonotic and infect humans, whereas HEV-5 and HEV-6 are only identified from swine. As a zoonotic agent, swine HEV is an emerging public health concern in many industrialized countries. Pigs are natural reservoir for HEV, consumption of raw or undercooked pork is an important route of foodborne HEV transmission. Occupational risks such as direct contact with infected pigs also increase the risk of HEV transmission in humans. Cross-species infection of HEV-3 and HEV-4 have been documented under experimental and natural conditions. Both swine HEV-3 and swine HEV-4 infect non-human primates, the surrogates of man. Swine HEV, predominantly HEV-3, can establish chronic infection in immunocompromised patients especially in solid organ transplant recipients. The zoonotic HEV-3, and to lesser extent HEV-4, have also been shown to cause neurological diseases and kidney injury. In this review, we focus on the epidemiology of swine HEV, host and viral determinants influencing cross-species HEV infection, zoonotic infection and its associated pork safety concern, as well as swine HEV-associated chronic infection and neurological diseases.

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.

Updates in Hepatitis E virus (HEV) field; lessons learned from human liver chimeric mice

Hepatitis E virus (HEV) is the most common cause of viral hepatitis globally, and it is an emerging pathogen in developed countries. In vivo studies of HEV have long been hindered due to the lack of an efficient small animal model. Recently, human liver chimeric mice were described as an elegant model to study chronic HEV infection. HEV infection was established in mice with humanized liver that were challenged with stool preparations containing HEV genotype (gt)1 and/or gt3. An increase in viral load and the level of HEV Ag in mouse samples were markers of active infection. Plasma-derived HEV preparations were less infectious. The kinetics of HEV ORF2 Ag during HEV infection and its impact on HEV diagnosis were described in this model. In addition, the nature of HEV particles and HEV ORF2 Ag were characterized. Moreover, humanized mice were used to study the impact of HEV infection on the hepatic innate transcriptome and evaluation of anti-HEV therapies. This review highlights recent advances in the HEV field gathered from well-established experimental mouse models, with an emphasis on this model as a tool for elucidating the course of HEV infection, the study of the HEV life cycle, the interaction of the virus with the host, and the evaluation of new anti-HEV therapies.

Detection of hepatitis E virus RNA in rats caught in pig farms from Northern Italy

Hepatitis E virus (HEV) strains belonging to the Orthohepevirus genus are divided into four species (A-D). HEV strains included in the Orthohepevirus A species infect humans and several other mammals. Among them, the HEV-3 and HEV-4 genotypes are zoonotic and infect both humans and animals, of which, pigs and wild boar are the main reservoirs. Viruses belonging to the Orthohepevirus C species (HEV-C) have been considered to infect rats of different species and carnivores. Recently, two studies reported the detection of HEV-C1 (rat HEV) RNA in immunocompromised and immunocompetent patients, suggesting a possible transmission of rat HEV to humans. The role of rats and mice as reservoir of HEV and the potential zoonotic transmission is still poorly known and deserves further investigation. To this purpose, in this study, the presence of HEV RNA was investigated in the intestinal contents and liver samples from 47 Black rats (Rattus rattus) and 21 House mice (Mus musculus) captured in four pig farms in Northern Italy. The presence of both Orthohepevirus A and C was investigated by the real-rime RT-PCR specific for HEV-1 to HEV-4 genotypes of Orthohepevirus A species and by a broad spectrum hemi-nested RT-PCR capable of detecting different HEV species including rat HEV. The intestinal content from two Black rats resulted positive for HEV-C1 RNA and for HEV-3 RNA, respectively. None of the House mice was HEV RNA positive. Sequence analyses confirmed the detection of HEV-C1, genotype G1 and HEV-3 subtype e. The viral strain HEV-3e detected in the rat was identical to swine HEV strains detected in the same farm. Liver samples were negative for the detection of either rat HEV or HEV-3.

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.

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.

Successful Establishment of Hepatitis E Virus Infection in Pregnant BALB/c Mice

Worldwide, the Hepatitis E virus (HEV) is the main pathogen of acute viral hepatitis, with an extremely high mortality in pregnant women. However, the pathogenesis of HEV infection in pregnant women remains largely unknown. We established an HEV-infected pregnant mice animal model to explore the adverse pregnancy outcomes of HEV infection. Mice were infected with HEV in their early, middle and late stages of pregnancy. HEV RNA was detected in the tissues (liver, spleen, kidney, colon, uterus and placenta) of pregnant mice. HEV antigens were also detected in these tissues of HEV-infected pregnant mice. Miscarriages (7/8, 87.5%) occurred in pregnant mice infected with HEV in the middle of pregnancy. Th1-biased immune status was found in these aborted mice. Vertical transmission was confirmed by HEV replication in the uterus and placenta, as well as in the positive HEV RNA and HEV antigen positive in fetal livers. The successful establishment of HEV infection in pregnant mice is beneficial for further study of HEV pathogenesis, especially the adverse pregnancy outcomes caused by HEV infection.

Different Outcomes of Experimental Hepatitis E Virus Infection in Diverse Mouse Strains, Wistar Rats, and Rabbits

Hepatitis E virus (HEV) is the causative agent of acute hepatitis E in humans in developing countries, but autochthonous cases of zoonotic genotype 3 (HEV-3) infection also occur in industrialized countries. In contrast to swine, rats, and rabbits, natural HEV infections in mice have not yet been demonstrated. The pig represents a well-established large animal model for HEV-3 infection, but a suitable small animal model mimicking natural HEV-3 infection is currently missing. Therefore, we experimentally inoculated C57BL/6 mice (wild-type, IFNAR^−/−, CD4^−/−, CD8^−/−) and BALB/c nude (nu/nu) mice, Wistar rats, and European rabbits with a wild boar-derived HEV-3 strain and monitored virus replication and shedding, as well as humoral immune responses. HEV RNA and anti-HEV antibodies were detected in one and two out of eight of the rats and all rabbits inoculated, respectively, but not in any of the mouse strains tested. Remarkably, immunosuppressive dexamethasone treatment of rats did not enhance their susceptibility to HEV infection. In rabbits, immunization with recombinant HEV-3 and ratHEV capsid proteins induced protection against HEV-3 challenge. In conclusion, the rabbit model for HEV-3 infection may serve as a suitable alternative to the non-human primate and swine models, and as an appropriate basis for vaccine evaluation studies.

Successful infection of BALB/c mice by a swine hepatitis E virus clone constructed with reverse genetics

Background

Hepatitis E virus (HEV) is a leading cause of hepatitis worldwide. However, its infection biology and pathogenesis remain largely elusive. Furthermore, no proven medication is available for treating hepatitis E. Robust experimental models are urgently required to advance the research of HEV infection. Because of the lacking of a sophisticated small animal model, this study aimed to establish a mouse model of HEV infection.

Methods

We constructed a full-length swine HEV cDNA clone of genotype 4 (named as pGEM-HEV) by reverse genetics approach. And we inoculated with HEV RNA in BALB/c mice to establish small animal model for HEV infection and pathogenesis studies.

Results

The capped RNA transcripts of pGEM-HEV prepared in vitro were replication-competent in HepG2 cells. Importantly, BALB/c mice intravenously inoculated with RNA transcripts of pGEM-HEV developed an active infection as shown by shedding viruses in feces, detectable negative strand of HEV in the liver, spleen and kidney, and causing liver inflammation.

Conclusion

In this study, we successfully established of BALB/c mice-based small animal model for HEV provides an opportunity to further understand HEV pathogenesis and to develop effective antiviral medications.

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.

Hepatitis E Virus Induces Hepatocyte Apoptosis via Mitochondrial Pathway in Mongolian Gerbils

Previous studies demonstrated that Mongolian gerbils can be infected by hepatitis E virus (HEV), which induces the hepatic injury. Here, the mitochondria in hepatocytes from HEV-infected gerbils were considerably swollen, thin cristae. After HEV infection, the activity of superoxide dismutase significantly decreased (p < 0.01), while malondialdehyde concentrations significantly increased, compared with those in the control group (p < 0.01). Adenosine triphosphatase levels decreased significantly in the hepatocyte of the inoculated groups, compared with those in control group (p < 0.05) at days 21, 28, 42 post-inoculation (dpi) as well. Furthermore, the levels of ATP synthetase ATP5A1 significantly decreased during HEV infection, compared with those in the control group (p < 0.05). According to the TdT mediated dUTP nick end labeling (TUNEL) detection, TUNEL positive hepatocytes increased in the inoculated group, compared with that in the control group (p < 0.05). Up-regulation of the mitochondrion-mediated apoptosis regulating proteins, Bax and Bcl-2, in the HEV-infected gerbils (p < 0.05) was observed. However, cytochrome c levels in mitochondria decreased, while this molecule was detected in the cytoplasm of the infected animals, in contrast to that in the control group. Apaf-1, and active caspase-9 and -3 levels were shown to be significantly higher in the inoculated group compared with those in the control group (p < 0.05). Taken together, our results demonstrated that HEV infection induces hepatocyte injuries and activity of the mitochondrial apoptotic pathway, which trigger the hepatocyte apoptosis in Mongolian gerbils.

Hepatitis E virus: advances and challenges

At least 20 million hepatitis E virus (HEV) infections occur annually, with >3 million symptomatic cases and ∼60,000 fatalities. Hepatitis E is generally self-limiting, with a case fatality rate of 0.5-3% in young adults. However, it can cause up to 30% mortality in pregnant women in the third trimester and can become chronic in immunocompromised individuals, such as those receiving organ transplants or chemotherapy and individuals with HIV infection. HEV is transmitted primarily via the faecal-oral route and was previously thought to be a public health concern only in developing countries. It is now also being frequently reported in industrialized countries, where it is transmitted zoonotically or through organ transplantation or blood transfusions. Although a vaccine for HEV has been developed, it is only licensed in China. Additionally, no effective, non-teratogenic and specific treatments against HEV infections are currently available. Although progress has been made in characterizing HEV biology, the scarcity of adequate experimental platforms has hampered further research. In this Review, we focus on providing an update on the HEV life cycle. We will further discuss existing cell culture and animal models and highlight platforms that have proven to be useful and/or are emerging for studying other hepatotropic (viral) pathogens.

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.

Hepatitis E Virus Infects Neurons and Brains

Hepatitis E virus (HEV), as a hepatotropic virus, is supposed to exclusively infect the liver and only cause hepatitis. However, a broad range of extrahepatic manifestations (in particular, idiopathic neurological disorders) have been recently reported in association with its infection. In this study, we have demonstrated that various human neural cell lines (embryonic stem cell-derived neural lineage cells) induced pluripotent stem cell-derived human neurons and primary mouse neurons are highly susceptible to HEV infection. Treatment with interferon-α or ribavirin, the off-label antiviral drugs for chronic hepatitis E, exerted potent antiviral activities against HEV infection in neural cells. More importantly, in mice and monkey peripherally inoculated with HEV particles, viral RNA and protein were detected in brain tissues. Finally, patients with HEV-associated neurological disorders shed the virus into cerebrospinal fluid, indicating a direct infection of their nervous system. Thus, HEV is neurotropic in vitro, and in mice, monkeys, and possibly humans. These results challenge the dogma of HEV as a pure hepatotropic virus and suggest that HEV infection should be considered in the differential diagnosis of idiopathic neurological disorders.

Molecular and structural changes related to hepatitis E virus antigen and its expression in testis inducing apoptosis in Mongolian gerbil model

Hepatitis E virus (HEV) infection has been associated with a wide range of extrahepatic manifestations, so this study was designed to examine the effect and role of HEV on structural and molecular changes in the testicular tissues of Mongolian gerbils experimentally infected with swine HEV. HEV RNA was first detected in testis at 14 days post-inoculation and reached a peak between 28 and 42 days later with viral load between 3.12 and 6.23 logs/g by PCR assays. Changes including vacuolation, sloughing of germ cells, formation of multinuclear giant cells, degeneration, necrosis of tubules and damaged blood-testis barrier were observed through transmission electron microscopy. HEV ORF2 antigen was detected in the sperm cell cytoplasm along with decrease in relative protein of zonula occludens-1 through immunohistochemistry. HEV ORF3 antigen and ZO-1 protein were detectable by Western blotting. Lower (P<.05) serum testosterone and higher (P<.05) blood urea nitrogen level was observed in inoculated Mongolian gerbils. Likewise, increased (P<.05) germ cell apoptosis rate was detected with significant increased expression of Fas-L and Fas in HEV-inoculated groups at each time points. Up-regulation (P<.05 or P<.01) in mRNA level of Fas-L, Fas, Bax, Bcl-2 and caspase-3 was observed in HEV RNA-positive testes. Our study demonstrated that after experimental inoculation, HEV can be detected in testis tissues and viral proteins produce structural and molecular changes that in turn disrupt the blood-testis barrier and induce germ cell apoptosis.

Public health risks associated with hepatitis E virus (HEV) as a food-borne pathogen

Hepatitis E virus (HEV) is an important infection in humans in EU/EEA countries, and over the last 10 years more than 21,000 acute clinical cases with 28 fatalities have been notified with an overall 10-fold increase in reported HEV cases; the majority (80%) of cases were reported from France, Germany and the UK. However, as infection in humans is not notifiable in all Member States, and surveillance differs between countries, the number of reported cases is not comparable and the true number of cases would probably be higher. Food-borne transmission of HEV appears to be a major route in Europe; pigs and wild boars are the main source of HEV. Outbreaks and sporadic cases have been identified in immune-competent persons as well as in recognised risk groups such as those with pre-existing liver damage, immunosuppressive illness or receiving immunosuppressive treatments. The opinion reviews current methods for the detection, identification, characterisation and tracing of HEV in food-producing animals and foods, reviews literature on HEV reservoirs and food-borne pathways, examines information on the epidemiology of HEV and its occurrence and persistence in foods, and investigates possible control measures along the food chain. Presently, the only efficient control option for HEV infection from consumption of meat, liver and products derived from animal reservoirs is sufficient heat treatment. The development of validated quantitative and qualitative detection methods, including infectivity assays and consensus molecular typing protocols, is required for the development of quantitative microbial risk assessments and efficient control measures. More research on the epidemiology and control of HEV in pig herds is required in order to minimise the proportion of pigs that remain viraemic or carry high levels of virus in intestinal contents at the time of slaughter. Consumption of raw pig, wild boar and deer meat products should be avoided.

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.

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.

Characterization of hepatitis E virus infection in tree shrew (Tupaia belangeri chinensis)

Background

Hepatitis E virus (HEV) is a major cause of hepatitis in developing countries and poses a threat to public health worldwide. Tree shrew (Tupaia belangeri chinensis) is a useful animal model in studies on hepatitis viruses, such as hepatitis B and C viruses. However, the use of this animal model for HEV research is yet to be developed.

Methods

Tree shrews were intravenously (IV) injected with swine genotype 4 HEV or infected by contact-exposure to IV infected tree shrews. RT-nPCR was performed to detect HEV RNA in the feces, tissues, and blood. HEV capsid protein in the different tissues was detected by Western blot and estimated by quantitative RT-PCR. Anti-HEV antibodies were determined by ELISA. Liver damages were evaluated by histopathologic examination and analysis of liver-specific enzymes activities.

Results

Both negative and positive strands of HEV RNA were detected in the feces of the HEV-infected or contact-exposed tree shrews 3–4 days post-inoculation. HEV RNA was detectable in the liver, spleen, kidneys, and bile. Virusemia developed in all the HEV-infected tree shrews. HEV capsid protein was expressed in the liver, spleen, and kidneys. The histological examination and analysis of liver-specific enzymes activities showed that HEV caused acute liver lesions in the tree shrews. Meanwhile, the infected tree shrews showed positive IgG and IgM antibodies.

Conclusions

Tree shrews are susceptible to HEV and may be useful animal models for HEV experimental infection studies on pathogenesis or preclinical drug development.

Antigen detection and apoptosis in Mongolian gerbil's kidney experimentally intraperitoneally infected by swine hepatitis E virus

We examined the effect of hepatitis E virus (HEV) on the renal tissue pathogenesis, morphological damages and related molecular mechanisms following swine HEV suspension intraperitoneally inoculation in Mongolian gerbils. The microscopic and ultramicroscopic analyses of kidney tissue structure were carried out at different points after inoculation of HEV. The immunohistochemistry, real-time PCR and Western blot were performed to explore the molecular mechanisms associated with HEV presence in the renal tissues. Real-time PCR revealed that the copies of HEV RNA in the kidney were detected at 7 dpi, and peaked at 14 dpi at a concentration was 7.18 logs g(-1), with detection of HEV ORF2 antigen by immunohistochemistry. Hematoxylin and eosin (HE) staining showed pathological lesions including glomerular atrophy, degeneration, edema and necrosis of renal tubular epithelial cells and Mallory and Sirius red staining indicated the presence of collagen fibers and fibrosis in kidney tissues of inoculated gerbils. Ultrastructural studies of basal membrane of renal tubules demonstrated the rough and uneven with mitochondria swelling and vacuolation in the tissues of HEV inoculated animals. Similarly, significantly higher number of (TUNEL)-positive cells were seen in renal tubule tissues compared to control group. Moreover, immuno histochemical results indicated that significant increase expression of the B-cell lymphoma 2 (Bcl-2), Bcl-2 associated X protein (Bax), FAS and Caspase-3 in HEV inoculated Mongolian gerbils at each time points. Relative mRNA expression by real-time PCR revealed a significantly higher (P<0.05) mRNA level of BAX, Bcl-2 and caspase-3 transcription in HEV inoculated Mongolian gerbils. Our results demonstrates that activation of mitochondria and Caspase-3 protease might be induced the apoptosis which subsequently cause the necrosis and cell death of renal epithelial cells during acute phase of HEV infection in HEV inoculated Mongolian gerbils.

Effect of swine hepatitis E virus on the livers of experimentally infected Mongolian gerbils by swine hepatitis E virus

Previous studies have shown that hepatitis E virus (HEV) can be transmitted between rats, pigs, cattle, rabbits, chicken, cats, and deer. Because wild and domestic rodents have anti-HEV antibodies, they are considered potential reservoirs of HEV. In the current study, Mongolian gerbils were experimentally infected with swine hepatitis E virus and the effects of this infection were investigated. After inoculation with HEV, the liver-to-body weight ratio increased at 7 dpi. Mongolian gerbils demonstrated significant increase (p<0.05) in Aspartate Transaminase (AST), alanine transaminase (ALT) and total bilirubin (T-BIL) concentrations in the sera, and HEV IgG was detected at 21 days post-inoculation (dpi). Real-time PCR revealed that the copies of HEV RNA in the liver were detected at 7 dpi, and peaked at 28 dpi at a concentration of 7.73 logs g(-1). Using both light and electron microscopy, hepatic lesions were observed in the HEV inoculated animals. In the experimental group, characteristic viral hepatitis lesions were prominent in the liver. HEV antigen was detected in the liver by immunohistochemistry, and HEV ORF3 antigen was detectable in liver by Western blot. These results clearly demonstrate that viral load of HEV in livers was dynamic, and ultrastructural hepatic injury in HEV infected Mongolian gerbils and anti-HEV IgG positive seroconversion were observed during infection.

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.

Experimental infection of Z:ZCLA Mongolian gerbils with human hepatitis E virus

AIM: To investigate whether Z:ZCLA Mongolian gerbils are readily susceptible to infection by human hepatitis E virus (HEV).

METHODS: Z:ZCLA Mongolian gerbils were infected with a clinical HEV strain isolated from an acute hepatitis E patient, and virus pathogenesis was assessed in this host. Non-infected gerbils served as the control group. Feces samples from gerbils were collected weekly for reverse transcription-nested polymerase chain reaction. Serum anti-HEV IgG and alanine aminotransferase (ALT) were detected by enzyme linked immunosorbent assay. At sacrifice, each animal’s liver, spleen and kidney were collected for histopathologic examination.

RESULTS: HEV-infected gerbils showed fatigue, with histopathological changes observed in the liver, spleen and kidney. HEV RNA was detected in fecal samples taken at day 7 after inoculation and the detectable levels lasted out to day 42 after inoculation. Interestingly, ALT levels were only moderately increased in the HEV-infected animals compared with the non-infected control group.

CONCLUSION: Z:ZCLA Mongolian gerbils are susceptible to human HEV.

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.

Infectivity of a genotype 4 hepatitis E virus cDNA clone by intrahepatic inoculation of laboratory rats

A cDNA clone of a genotype 4 swine hepatitis E virus (HEV) strain (SAAS-FX17), identified in Shanghai, has been constructed. Capped RNA transcripts were prepared in vitro and shown to be replication-competent in Huh7 cells. Sprague-Dawley (SD) rats administered the RNA transcripts by intrahepatic inoculation developed active infections as evidenced by fecal virus shedding and sero-conversion to anti-HEV. The former was first detected between 23 and 30 days post-inoculation (dpi) and persisted until 45 dpi. Sera of rats inoculated with RNA transcripts became anti-HEV positive between 30 and 40 dpi, and reverted to anti-HEV negative at 52 dpi. Our data indicate for the first time that intrahepatic inoculation of rats with RNA transcripts of an HEV cDNA clone may serve as an alternative animal model for HEV research.

Susceptibility of BALB/c-nu/nu mice and BALB/c mice to equine herpesvirus 9 infection

This study aimed to clarify the timing and infectivity of equine herpesvirus 9 (EHV-9) infection in BALB/c-nu/nu mice and their immunocompetent counterpart (BALB/c). Following intranasal inoculation with 10(5) PFU of EHV-9, specimens from 8 mice per group were collected at different times postinoculation (PI) and assessed using histopathology, immunohistochemistry for viral antigen, and quantitative real-time polymerase chain reaction for ORF30 gene expression. In BALB/c-nu/nu mice, EHV-9 antigen was abundant in olfactory epithelia of all inoculated animals, and in the olfactory bulb of 1 animal. In contrast, only 1 BALB/c mouse per time point had rhinitis, with mild to moderate immunopositivity starting from 12 to 48 h PI, followed by a gradual virus clearance at 72 h PI. Statistically, significant differences were noted in the immunohistochemistry reactions between the 2 mouse strains, indicating that BALB/c-nu/nu is more susceptible to infection. Relative expression levels of ORF30 gene in olfactory epithelia were significantly different between the 2 groups, with the exception of 12 h PI, when BALB/c-nu/nu animals showed dramatic increases in ORF30 gene expression level until 48 h PI, followed by a decline in expression level until the end of experiment. In contrast, the expression level in brains showed no differences between mouse strain except at 96 h PI. In both strains, the highest messenger RNA expression was detected at 48 h PI, followed by a decline in BALB/c mice, proving a rapid clearance of virus in BALB/c and a gradual slowing down of the increased expression levels in BALB/c-nu/nu.

Rabbit and human hepatitis E virus strains belong to a single serotype

Hepatitis E virus (HEV) is a zoonotic pathogen and all four established genotypes of HEV belong to a single serotype. The recently identified rabbit HEV is antigenically and genetically related to human HEV. It is unclear whether rabbit HEV belongs to the same serotype as human HEV. The purpose of this study was to determine the serotypic relationship between rabbit and human HEVs. HEV ORF2 recombinant capsid protein p166 (amino acids 452-617) of four known HEV genotypes and rabbit HEV were used to induce immune serum, which were evaluated for their ability to neutralize human HEV genotype 1, 4, and rabbit HEV strains by an in vitro PCR-based HEV neutralization assay. Immune sera of five kinds of p166 proteins were all found to neutralize or cross-neutralize the three different HEV strains, suggesting a common neutralization epitope(s) existing between human and rabbit HEV. Rabbit models of a second-passage rabbit HEV strain, JS204-2, and a genotype 4 human HEV strain, NJ703, were established as evidenced by fecal virus shedding, viremia and anti-HEV IgG seroconversion. Six rabbits, recovered from JS204 infection, were challenged with NJ703, and another six recovered from NJ703 infection were challenged with JS204-2. After challenge, viremia was not detected, shorter fecal virus shedding durations and obvious early stage declines in anti-HEV IgG values were observed. The results from this study indicate that rabbit HEV belongs to the same serotype as human HEV.

Rabbit as a novel animal model for hepatitis E virus infection and vaccine evaluation

Background

The identification of hepatitis E virus (HEV) from rabbits motivated us to assess the possibility of using rabbits as a non-human primate animal model for HEV infection and vaccine evaluation.

Methodology/Principal Findings

First, 75 rabbits were inoculated with seven strains of genotypes 1, 3, 4, and rabbit HEV, to determine the appropriate strain, administrative route and viral dosage. Second, 15 rabbits were randomly divided into three groups and vaccinated with 0 µg (placebo), 10 µg and 20 µg of HEV candidate vaccine, HEV p179, respectively. After three doses of the vaccination, the rabbits were challenged with 3.3×10⁵ genome equivalents of genotype 4 HEV strain H4-NJ703. The strain of genotype 1 HEV was not found to be infectious for rabbits. However, approximately 80% of the animals were infected by two rabbit HEV strains. All rabbits inoculated with a genotype 3 strain were seroconverted but did not show viremia or fecal viral shedding. Although two genotype 4 strains, H4-NJ153 and H4-NJ112, only resulted in part of rabbits infected, another strain of genotype 4, H4-NJ703, had an infection rate of 100% (five out of five) when administrated intravenously. However, only two out of fifteen rabbits showed virus excretion and seroconversion when inoculated orally with H4-NJ703 of three different dosages. In the vaccine evaluation study, rabbits vaccinated with 20 µg of the HEV p179 produced anti-HEV with titers of 1∶10⁴–1∶10⁵ and were completely protected from infection. Rabbits vaccinated with 10 µg produced anti-HEV with titers of 1∶10³–1∶10⁴ and were protected from hepatitis, but two out of the five rabbits showed virus shedding.

Conclusions/Significance

Rabbits may be served as an alternative to the non-human primate models for HEV infection and vaccine evaluation when certain virus strains, appropriate viral dosages, and the intravenous route of inoculation are selected.

Frequent detection and characterization of hepatitis E virus variants in wild rats (Rattus rattus) in Indonesia

One hundred sixteen rats (Rattus rattus) captured in Indonesia from 2011 to 2012 were investigated for the prevalence of hepatitis E virus (HEV)-specific antibodies and HEV RNA. Using an ELISA based on HEV genotype 4 with an ad hoc cutoff value of 0.500, 18.1 % of the rats tested positive for anti-HEV IgG. By nested RT-PCR, 14.7 % of the rats had rat HEV RNA, and none were positive for HEV genotype 1-4. A high HEV prevalence among rats was associated with lower sanitary conditions in areas with a high population density. Sixteen of the 17 HEV isolates obtained from infected rats showed >93.0 % nucleotide sequence identity within the 840-nucleotide ORF1-ORF2 sequence and were most closely related to a Vietnamese strain (85.9-87.9 % identity), while the remaining isolate differed from known rat HEV strains by 18.8-23.3 % and may belong to a novel lineage of rat HEV. These results suggest a wide distribution of rat HEV with divergent genomes.

Molecular biology and replication of hepatitis E virus

Hepatitis E virus (HEV), a single-stranded, positive-sense RNA virus, is responsible for acute hepatitis E epidemics in many developing countries, and the virus is also endemic in some industrialized countries. Hepatitis E is a recognized zoonotic disease, and several animal species, including pigs, are potential reservoirs for HEV. The genome of HEV contains three open reading frames (ORFs). ORF1 encodes the nonstructural proteins, ORF2 encodes the capsid protein, and ORF3 encodes a small multifunctional protein. The ORF2 and ORF3 proteins are translated from a single, bicistronic mRNA. The coding sequences for these two ORFs overlap each other, but neither overlaps with ORF1. Whereas the mechanisms underlying HEV replication are poorly understood, the construction of infectious viral clones, the identification of cell lines that support HEV replication, and the development of small animal models have allowed for more detailed study of the virus. As result of these advances, recently, our understanding of viral entry, genomic replication and viral egress has improved. Furthermore, the determination of the T=1 and T=3 structure of HEV virus-like particles has furthered our understanding of the replication of HEV. This article reviews the latest developments in the molecular biology of HEV with an emphasis on the genomic organization, the expression and function of genes, and the structure and replication of HEV.

Characterization of hepatitis E virus recombinant ORF2 proteins expressed by vaccinia viruses

Hepatitis E virus (HEV), an enterically transmitted pathogen, is one of the major causes of acute hepatitis in humans worldwide, being responsible for outbreaks and epidemics in regions with suboptimal sanitary conditions, in many of which it is endemic. In industrialized countries, hepatitis E is rarely reported, but recent studies have revealed quite high human seroprevalence rates and the possibility of porcine zoonotic transmission. There is currently no specific therapy or licensed vaccine against HEV infection, and little is known about its intracellular growth cycle, as until very recently no efficient cell culture system has been available. In the present study, vaccinia viruses have been used to express recombinant HEV ORF2 proteins, allowing the study of their glycosylation patterns and subcellular localization. Furthermore, the expressed proteins have been shown to be good antigens for diagnostic purposes and to elicit high and long-lasting specific anti-HEV titers of antibodies in mice that are passively transferred to the offspring by both transplacental and lactation routes.

Hepatitis E virus in Norway rats (Rattus norvegicus) captured around a pig farm

Background

Hepatitis E virus (HEV) transmitted via the oral route through the consumption of contaminated water or uncooked or undercooked contaminated meat has been implicated in major outbreaks. Rats may play a critical role in HEV outbreaks, considering their negative effects on environmental hygiene and food sanitation. Although the serological evidence of HEV infection in wild rodents has been reported worldwide, the infectivity and propagation of HEV in wild rats remain unknown. To investigate if rats are a possible carrier of HEV, we studied wild Norway rats (Rattus norvegicus) that were caught near a pig farm, where HEV was prevalent among the pigs.

Methods

We examined 56 Norway rats for HEV. RNA from internal organs was examined for RT-PCR and positive samples were sequenced. Positive tissue samples were incubated with A549 cell line to isolate HEV. Anti-HEV antibodies were detected by ELISA.

Results

Sixteen rats were seropositive, and the HEV RNA was detected in 10 of the 56 rats. Sequencing of the partial ORF1 gene from 7 samples resulted in partially sequenced HEV, belonging to genotype 3, which was genetically identical to the HEV prevalent in the swine from the source farm. The infectious HEVs were isolated from the Norway rats by using the human A549 cell line.

Conclusions

There was a relatively high prevalence (17.9%) of the HEV genome in wild Norway rats. The virus was mainly detected in the liver and spleen. The results indicate that these animals might be possible carrier of swine HEV in endemic regions. The HEV contamination risk due to rats needs to be examined in human habitats.

Pathogenetic elements of hepatitis E and animal models of HEV infection

The pathogenesis of HEV infection responsible for liver pathology and clinical disease is not well understood. The main target for the virus is the hepatocyte, where it replicates and is released to bile and gastrointestinal tract. Viremia is regularly seen during the virus replication. The exact mechanism of hepatocytic death is uncertain. In experimentally infected non-human primates, the peak of liver lesions, measured by alanine aminotransferase activity elevation, is concordant with the virus disappearance from stool at the time of dynamic humoral immune response; the role of cellular immunity has not been researched adequately, especially HEV-specific immune response in the liver. Non-human primates (chimpanzees, rhesus and cynomolgus macaques) are most widely used animal models for the study of HEV infection, its pathogenesis and vaccine trials. Several other animal models including pigs, rabbits and chickens have recently been established for the study of various aspects of HEV infection. Infectivity studies in susceptible primates were of significance in molecular studies of the virus itself. Preclinical vaccine trials with the use of various recombinant HEV capsid proteins and viral DNA established basic platform for formulation of HEV vaccine applied in HEV-endemic regions (China, Nepal).

From barnyard to food table: the omnipresence of hepatitis E virus and risk for zoonotic infection and food safety

Hepatitis E virus (HEV) is an important but extremely understudied pathogen. The mechanisms of HEV replication and pathogenesis are poorly understood, and a vaccine against HEV is not yet available. HEV is classified in the family Hepeviridae consisting of at least four recognized major genotypes. Genotypes 1 and 2 HEV are restricted to humans and associated with epidemics in developing countries, whereas genotypes 3 and 4 HEV are zoonotic and responsible for sporadic cases worldwide. The identification and characterization of a number of animal strains of HEV from pigs, chickens, rabbits, rats, mongoose, deer, and possibly cattle and sheep have significantly broadened the host range and diversity of HEV. The demonstrated ability of cross-species infection by some animal strains of HEV raises public health concerns for zoonotic HEV infection. Pigs are a recognized reservoir for HEV, and pig handlers are at increased risk of zoonotic HEV infection. Sporadic cases of hepatitis E have been definitively linked to the consumption of raw or undercooked animal meats such as pig livers, sausages, and deer meats. In addition, since large amounts of viruses excreted in feces, animal manure land application and runoffs can contaminate irrigation and drinking water with concomitant contamination of produce or shellfish. HEV RNA of swine origin has been detected in swine manure, sewage water and oysters, and consumption of contaminated shellfish has also been implicated in sporadic cases of hepatitis E. Therefore, the animal strains of HEV pose not only a zoonotic risk but also food and environmental safety concerns.