A549 and PLC/PRF/5 cells can support the efficient propagation of swine and wild boar hepatitis E virus (HEV) strains: demonstration of HEV infectivity of porcine liver sold as food

Evaluation of Food Homogenates on Cell Survival In Vitro

A critical review on the approaches to assess the infectivity of the Hepatitis E virus (HEV) in food recommended that a cell culture-based method should be developed. Due to the observations that viral loads in food may be low, it is important to maximise the potential for detection of HEV in a food source in order to fully assess infectivity. To do so, would require minimal processing of any target material. In order to proceed with the development of an infectivity culture method that is simple, robust and reproducible, there are a number of points to address; one being to assess if food homogenates are cytotoxic to HEV susceptible target cells. Food matrices previously shown to have detectable HEV nucleic acid were selected for analysis and assessed for their effect on the percentage survival of three cell lines commonly used for infectivity assays. Target cells used were A549, PLC/PRF/5 and HepG2 cells. The results showed that, as expected, various food homogenates have differing effects on cells in vitro. In this study, the most robust cell line over a time period was the A549 cell line in comparison to HepG2, with PLC/PRF/5 cells being the most sensitive. Overall, this data would suggest that FH can be left in contact with A549 cells for a period of up to 72 h to maximise the potential for testing infection. Using food homogenates directly would negate any concerns over losing virus as a result of any additional processing steps.

A Multifaceted Approach for Evaluating Hepatitis E Virus Infectivity In Vitro: Cell Culture and Innovative Molecular Methods for Integrity Assessment

Hepatitis E virus is a prominent cause of viral hepatitis worldwide. In Western countries, most infections are asymptomatic. However, acute self-limiting hepatitis and chronic cases in immunocompromised individuals can occur. Studying HEV is challenging due to its difficulty to grow in cell culture. Consequently, the detection of the virus mainly relies on RT-qPCR, which cannot differentiate between infectious and non-infectious particles. To overcome this problem, methods assessing viral integrity offer a possible solution to differentiate between intact and damaged viruses. This study aims at optimizing existing HEV cell culture models and RT-qPCR-based assays for selectively detecting intact virions to establish a reliable model for assessing HEV infectivity. In conclusion, these newly developed methods hold promise for enhancing food safety by identifying approaches for inactivating HEV in food processing, thereby increasing food safety measures.

Infection Dynamics and Genomic Mutations of Hepatitis E Virus in Naturally Infected Pigs on a Farrow-to-Finish Farm in Japan: A Survey from 2012 to 2021

Hepatitis E virus (HEV) causes acute or chronic hepatitis in humans. Pigs are the primary reservoir for zoonotic HEV genotypes 3 and 4 worldwide. This study investigated the infection dynamics and genomic mutations of HEV in domestic pigs on a farrow-to-finish pig farm in Japan between 2012 and 2021. A high prevalence of anti-HEV IgG antibodies was noted among pigs on this farm in 2012, when the survey started, and persisted for at least nine years. During 2012-2021, HEV RNA was detected in both serum and fecal samples, indicating active viral replication. Environmental samples, including slurry samples in manure pits, feces on the floor, floor and wall swabs in pens, and dust samples, also tested positive for HEV RNA, suggesting potential sources of infection within the farm environment. Indeed, pigs raised in HEV-contaminated houses had a higher rate of HEV infection than those in an HEV-free house. All 104 HEV strains belonged to subgenotype 3b, showing a gradual decrease in nucleotide identities over time. The 2012 (swEJM1201802S) and 2021 (swEJM2100729F) HEV strains shared 97.9% sequence identity over the entire genome. Importantly, the swEJM2100729F strain efficiently propagated in human hepatoma cells, demonstrating its infectivity. These findings contribute to our understanding of the prevalence, transmission dynamics, and genetic characteristics of HEV in domestic pigs, emphasizing the potential risks associated with HEV infections and are crucial for developing effective strategies to mitigate the risk of HEV infection in both animals and humans.

Hepatitis E virus in pork meat products and exposure assessment in Belgium

Zoonotic hepatitis E virus (HEV) genotype 3 infections are the predominant cause of acute viral hepatitis in Europe, mostly associated with the consumption of HEV contaminated pork meat. In this study we looked at the HEV RNA positivity rate of pork meat products readily available from Belgian supermarkets and evaluated the overall HEV consumer exposure in a Belgian context. Two basic assessments were performed in a 'worst-case' scenario setting: one solely focusing on the contamination level of the product itself (ingredients and processing parameters) and another estimating the overall consumer exposure, taking into account consumption habits in Belgium. Non-thermal-processed ready-to-eat (i.e. ready for consumption without additional cooking step by consumer) pork meat products (e.g. raw dried sausages), had a high estimated HEV contamination level, while thermal-processed ready-to-eat pork meat products (e.g. pork liver pâté) had the highest overall consumer exposure estimates. Following these assessments, pork liver pâtés, raw dried hams and raw dried sausages (n = 54) were purchased from Belgian supermarkets (n = 3) and analyzed for HEV RNA by RT-PCR. In total, 31 % (n = 17) products tested positive. HEV RNA was found in 65 % of the pork liver pâtés, 15 % of raw dried hams and 0 % of raw dried sausages. Phylogenetic analysis of four isolates (all gt3c) from pork liver pâté samples showed similarities with human clinical cases from Germany and Belgium.

In Vitro Replication of Swine Hepatitis E Virus (HEV): Production of Cell-Adapted Strains

The hepatitis E caused by the virus HEV of genotypes HEV-3 and HEV-4 is a zoonotic foodborne disease spread worldwide. HEV is currently classified into eight different genotypes (HEV-1-8). Genotypes HEV-3 and HEV-4 are zoonotic and are further divided into subtypes. Most of the information on HEV replication remains unknown due to the lack of an efficient cell cultivation system. Over the last couple of years, several protocols for HEV cultivation have been developed on different cell lines; even if they were troublesome, long, and scarcely reproducible, they offered the opportunity to study the replicative cycle of the virus. In the present study, we aimed to obtain a protocol ready to use viral stock in serum free medium that can be used with reduced time of growth and without any purification steps. The employed method allowed isolation and cell adaptation of four swine HEV-3 strains, belonging to three different subtypes. Phylogenetic analyses conducted on partial genome sequences of in vitro isolated strains did not reveal any insertion in the hypervariable region (HVR) of the genomes. A limited number of mutations was acquired in the genome during the virus growth in the partial sequences of Methyltransferase (Met) and ORF2 coding genes.

HEV Cell Culture

Cell culture is an important research method in virology. Although many attempts have been conducted to culture HEV in cells, only a few cell culture systems were considered to be efficient enough for usage. Concentration of virus stocks, host cells, and medium components affects the culture efficiency and the genetic mutations during HEV passage were found to be associated with the increased virulence in cell culture. As an alternative method for traditional cell culture, the infectious cDNA clones were constructed. The viral thermal stability, factors that impact the host range, post-translation of viral proteins, and function of different viral proteins were studied using the infectious cDNA clones. HEV cell culture studies on progeny virus showed that the viruses secreted from host cells have an envelope and its formation was associated with pORF3. This result explained the phenomenon that virus could infect host cells in the presence of anti-HEV antibodies.

Viral hepatitis in pregnancy

Viral hepatitis is caused by a heterogenous group of viral agents representing a wide range of phylogenetic groups. Many viruses can involve the liver and cause liver injury but only a subset are delineated as 'hepatitis viruses' based upon their primary site of replication and tropism for hepatocytes which make up the bulk of the liver cell population. Since their discovery, beginning with the agent that caused serum hepatitis in the 1960s, the alphabetic designations have been utilized. To date, we have five hepatitis viruses, A through E, though it is postulated that others may exist. This chapter will focus on those viruses. Note that hepatitis D is included as a subset of hepatitis B, as it cannot exist without concurrent hepatitis B infection. Pregnancy has the potential to affect all aspects of these viral agents due to the unique immunologic and physiologic changes that occur during and after the gestational period. In this review, we will discuss the most common viral hepatitis and their effects during pregnancy.

Cell Culture Isolation and Whole Genome Characterization of Hepatitis E Virus Strains from Wild Boars in Germany

Infection with hepatitis E virus (HEV) can cause acute and chronic hepatitis in humans. The HEV genotype 3 can be zoonotically transmitted from animals to humans, with wild boars representing an important reservoir species. Cell culture isolation of HEV is generally difficult and mainly described for human isolates so far. Here, five sera and five liver samples from HEV-RNA-positive wild boar samples were inoculated onto PLC/PRF/5 cells, incubated for 3 months and thereafter passaged for additional 6 weeks. As demonstrated by RT-qPCR, immunofluorescence and immune electron microscopy, virus was successfully isolated from two liver samples, which originally contained high HEV genome copy numbers. Both isolates showed slower growth than the culture-adapted HEV strain 47832c. In contrast to this strain, the isolated strains had no insertions in their hypervariable genome region. Next generation sequencing using an HEV sequence-enriched library enabled full genome sequencing. Strain Wb108/17 belongs to subtype 3f and strain Wb257/17 to a tentative novel subtype recently described in Italian wild boars. The results indicate that HEV can be successfully isolated in cell culture from wild boar samples containing high HEV genome copy numbers. The isolates may be used further to study the zoonotic potential of wild boar-derived HEV subtypes.

Porcine Blood and Liver as Sporadic Sources of Hepatitis E Virus (HEV) in the Production Chain of Offal-Derived Foodstuffs in Poland

Pig's blood and liver are valuable edible slaughter by-products which are also the major ingredients of offal-derived foodstuffs. The aim of the study was an evaluation of the occurrence of hepatitis E virus (HEV) and porcine adenovirus (pAdV) as an index virus of faecal contamination in pig's blood and liver for human consumption. In total, 246 samples of retail liver (n = 100) and pooled pig's blood (n = 146) were analysed for the presence of HEV and pAdV. Blood samples were individually collected from 1432 pigs at slaughter age. Viral genomic material, including RNA of a sample process control virus was isolated from food samples using a QIAamp® Viral RNA Mini Kit. Virus-specific IAC-controlled real-time PCR methods were used for detection of target viruses. HEV RNA was found in 6 (2.4%; 95% CI: 0.9-5.2) out of 246 samples of tested foodstuffs. The virus was detected in pig's blood (3.4%; 95% CI: 1.1-7.8) and liver (1.0%; 95% CI: 0.0-5.0) with no significant differences observed in the frequency of its occurrence between the two by-products (t = 1.33; p = 0.182 > 0.05); however PAdV was detected more frequently in pig's blood than in liver (t = 4.65; p = 0.000 < 0.05). The HEV strains belonged to the 3f and 3e subtype groups and the pAdV strains were assigned to serotype 5. PAdV was detected in pigs regardless of the farm size from which they originated. The number of animals raised on the farm (the farm size) had no influence on the occurrence of HEV or pAdV infections in pigs (F = 0.81, p = 0.447 > 0.05 for HEV; F = 0.42, p = 0.655 > 0.05 for pAdV). Although HEV was detected in pig's offal only sporadically, consumers cannot treat its occurrence with disregard as it demonstrates that HEV-contaminated pig tissues can enter the food chain.

Inhibition of hepatitis E virus replication by zinc-finger antiviral Protein synergizes with IFN-β

Hepatitis E virus (HEV) infection is the most common cause of acute viral hepatitis worldwide. However, host-HEV interactions have yet to be fully understood. Zinc-finger antiviral protein (ZAP) is a novel interferon (IFN)-stimulated gene product that inhibits a variety of viruses in synergy with IFN-β. To evaluate the role of ZAP in HEV infection, its expressions in HEV-infected patients and in cell cultures were measured. We report a significant inhibition of ZAP expression in patients with HEV genotype four acute infection. The expression of ZAP in the HEV life cycle was monitored in cultures of HEV-infected cells. Results indicated that the ZAP level decreased significantly after HEV infection. ZAP over-expression inhibited HEV replication, whereas its knockdown by RNA interference significantly increased HEV RNA. These suggest that ZAP serves as an antiviral in HEV infection. Moreover, silencing ZAP decreased IFN regulatory factor 3 (IRF3) phosphorylation in HEV-infected cells treated with poly(I:C), indicating that ZAP synergizes with IFN-β. In conclusion, ZAP is an important anti-HEV host factor and in synergy with IFN-β, inhibits HEV replication.

Foodborne transmission of hepatitis A and hepatitis E viruses: A literature review

Foodborne viruses have been recognized as a growing concern to the food industry and a serious public health problem. Hepatitis A virus (HAV) is responsible for the majority of viral outbreaks of food origin worldwide, while hepatitis E virus (HEV) has also been gaining prominence as a foodborne viral agent in the last years, due to its zoonotic transmission through the consumption of uncooked or undercooked infected meat or derivatives. However, there is a lack of scientific reports that gather all the updated information about HAV and HEV as foodborne viruses. A search of all scientific articles about HAV and HEV in food until March 2020 was carried out, using the keywords "HAV", "HEV", "foodborne", "outbreak" and "detection in food". Foodborne outbreaks due to HAV have been reported since 1956, mainly in the USA, and in Europe in recent years, where the number of outbreaks has been increasing throughout time, and nowadays it has become the continent with the highest foodborne HAV outbreak report. Investigation and detection of HAV in food is more recent, and the first detections were performed in the 1990s decade, most of them carried out on seafood, first, and frozen food, later. On the other hand, HEV has been mainly looked for and detected in food derived from reservoir animals, such as meat, sausages and pate of pigs and wild boars. For this virus, only isolated cases and small outbreaks of foodborne transmission have been recorded, most of them in industrialized countries, due to HEV genotype 3 or 4. Virus detection in food matrices requires special processing of the food matrix, followed by RNA detection by molecular techniques. For HAV, a real-time PCR has been agreed as the standard method for virus detection in food; in the case of HEV, a consensus assay for its detection in food has not been reached yet. Our investigation shows that there is still little data about HAV and HEV prevalence and frequency of contamination in food, prevalent viral strains, and sources of contamination, mainly in developing countries, where there is no research and legislation in this regard. Studies on these issues are needed to get a better understanding of foodborne viruses, their maintenance and their potential to cause diseases.

Development of BacMam Induced Hepatitis E Virus Replication Model in Hepatoma Cells to Study the Polyprotein Processing

The processing of polyprotein(s) to form structural and non-structural components remains an enigma due to the non-existence of an efficient and robust Hepatitis E Virus (HEV) culture system. We used the BacMam approach to construct an HEV replication model in which the HEV genome was cloned in the BacMam vector under the CMV promoter. The recombinant BacMam was used to infect Huh7 cells to transfer the HEV genome. HEV replication was authenticated by the presence of RNAs of both the polarity (+) and (−) and formation of hybrid RNA, a replication intermediate. The presence of genes for Papain-like Cysteine Protease (PCP), methyltransferase (MeT), RNA dependent RNA polymerase (RdRp), and ORF2 was confirmed by PCR amplification. Further, the infectious nature of the culture system was established as evidenced by the cross-infection of uninfected cells using the cell lysate from the infected cells. The HEV replication model was validated by detection of the ORF1 (Open Reading Frame1) encoded proteins, identified by Western blotting and Immunofluorescence by using epitope-specific antibodies against each protein. Consequently, discrete bands of 18, 35, 37, and 56 kDa corresponding to PCP, MeT, RdRp, and ORF2, respectively, were seen. Besides demonstrating the presence of non-structural enzymes of HEV along with ORF2, activity of a key enzyme, HEV-methyltransferase has also been observed. A 20% decrease in the replicative forms of RNA could be seen in presence of 100 μM Ribavirin after 48 h of treatment. The inhibition gradually increased from 0 to 24 to 48 h post-treatment. Summarily, infectious HEV culture system has been established, which could demonstrate the presence of HEV replicative RNA forms, the structural and non-structural proteins and the methyltransferase in its active form. The system may also be used to study the mechanism of action of Ribavirin in inhibiting HEV replication and develop a therapy.

Hepatitis E genotype 3 virus isolate from wild boar is capable of replication in non-human primate and swine kidney cells and mouse neuroblastoma cells

BACKGROUND

Wild boar-derived hepatitis E (HEV) genotype 3 virus has been successfully isolated in cell lines of human origin only. Considering the zoonotic potential and possible extrahepatic localisation of genotype 3 strain, it is important to investigate the viability of cell lines of different animal and tissue origins. Therefore, the objective of the present study was to determine the permissiveness of non-human primate (MARC-145 and Vero) and swine (PK-15) cell lines of kidney origin, and a mouse neuroblastoma (Neuro-2a) cell line for isolation of wild boar-derived HEV genotype 3.

RESULTS

This study showed that MARC-145, PK-15, Neuro-2a and Vero cell lines were permissive to wild boar-derived HEV genotype 3 subtype 3i harbouring viral genome equivalents of 1.12 × 10⁷ copies/ml, 2.38 × 10⁵ copies/ml, 2.97 × 10⁷ copies/ml and 4.01 × 10⁷ copies/ml after five serial passages respectively. In all permissive cell lines, HEV was continuously recovered from growth medium between five and at least 28 days post-infection. Peak loads of HEV genome equivalents were observed on days 7, 12, 19 and 30 in MARC-145 (2.88 × 10⁷ copies/ml), Vero (4.23 × 10⁶ copies/ml), Neuro-2a (3.15 × 10⁶ copies/ml) and PK-15 (2.24 × 10⁷ copies/ml) cell lines respectively. In addition, successful virus isolation was confirmed by immunofluorescence assay targeting HEV capsid protein and sequencing of HEV isolate retrieved from cell cultures.

CONCLUSIONS

This study showed that wild boar-derived HEV genotype 3 subtype 3i strain was capable of infecting cell lines of animal origin, including primate and porcine kidney cells (MARC-145, PK-15 and Vero), and mouse neuroblastoma cells (Neuro-2a), supporting the notion of the capacity of HEV genotype 3 to cross the species barrier and extra-hepatic localisation of the virus. These findings warrant further studies of tested cell lines to investigate their capacity as an efficient system for HEV propagation. HEV isolates from other wild animal hosts should be isolated on tested cell lines in order to generate more data on HEV transmission between wild animal populations and their role as sources of human infections.

Cell culture isolation of Hepatitis E Virus Genotype 3 Strain obtained from human feces

Hepatitis E virus (HEV) is considered one of the leading causes of acute viral hepatitis worldwide, and about 20 million infections and approximately 57 000 deaths occurred every year. However, little is known about the replicative virus cycle due to the absence of a consensus cell culture model. A549 cell line is considered susceptible to HEV genotype 3, however, both viral strain and cell culture conditions could affect the viral isolation in vitro. The objective of this work was to isolate in vitro an HEV-3 strain obtained from human feces. To this, a genotype 3 HEV strain previously identified by genetic characterization was inoculated in A549 monolayers, and incubated for two hours at 37 °C. Five days post-infection, cells were passaged (subcultured) for the first time, and serial passages were done on average every four days during 41 days. HEV replication was evaluated through RT-qPCR in each passage, and reinfection of the cell line with the viral progeny derived from A549 infected monolayers was assessed through immunofluorescence and RT-qPCR. Viral RNA was detected in each passage from infected monolayers, and the highest amount was found after 26 days (2 x 106 copies/μL). In reinfection assay, capsid antigen was detected perinuclearly and forming foci, and 1x104 copies/μL of viral RNA was detected after 96 hours post infection. This shows that HEV recovered from the cell lysate monolayers was infectious. This viral isolate offers a critical tool to study the unknown aspect of HEV infection.

Isolation of Subtype 3c, 3e and 3f-Like Hepatitis E Virus Strains Stably Replicating to High Viral Loads in an Optimized Cell Culture System

The hepatitis E virus (HEV) is transmitted via the faecal-oral route in developing countries (genotypes 1 and 2) or through contaminated food and blood products worldwide (genotypes 3 and 4). In Europe, HEV subtypes 3c, 3e and 3f are predominant. HEV is the leading cause of acute hepatitis globally and immunocompromised patients are particularly at risk. Because of a lack of cell culture systems efficiently propagating wild-type viruses, research on HEV is mostly based on cell culture-adapted isolates carrying uncommon insertions in the hypervariable region (HVR). While optimizing the cell culture system using the cell culture-adapted HEV strain 47832c, we isolated three wild-type strains derived from clinical specimens representing the predominant spectrum of HEV in Europe. The novel isolates 14-16753 (3c), 14-22707 (3e) and 15-22016 (3f-like) replicate to high viral loads of 10⁸, 10⁹ and 10^6.5 HEV RNA copies/mL at 14 days post-inoculation, respectively. In addition, they could be kept as persistently infected cell cultures with constant high viral loads (~10⁹ copies/mL) for more than a year. In contrast to the latest isolates 47832c, LBPR-0379 and Kernow-C1, the new isolates do not carry genome insertions in the HVR. Optimization of HEV cell culture identified amphotericin B, distinct salts and fetal calf serum (FCS) as important medium supplements. Overconfluent cell layers increased infectivity and virus production. PLC/PRF/5, HuH-7-Lunet BLR, A549 and HepG2/C3A supported replication with different efficiencies. The novel strains and optimized cell culture system may be useful for studies on the HEV life cycle, inactivation, specific drug and vaccine development.

Hepatitis E virus (HEV)-The Future

Hepatitis (HEV) is widely distributed in pigs and is transmitted with increasing numbers to humans by contact with pigs, contaminated food and blood transfusion. The virus is mostly apathogenic in pigs but may enhance the pathogenicity of other pig viruses. In humans, infection can lead to acute and chronic hepatitis and extrahepatic manifestations. In order to stop the emerging infection, effective counter-measures are required. First of all, transmission by blood products can be prevented by screening all blood donations. Meat and sausages should be appropriately cooked. Elimination of the virus from the entire pork production can be achieved by sensitive testing and elimination programs including early weaning, colostrum deprivation, Caesarean delivery, embryo transfer, treatment with antivirals, protection from de novo infection, and possibly vaccination. In addition, contaminated water, shellfish, vegetables, and fruits by HEV-contaminated manure should be avoided. A special situation is given in xenotransplantation using pig cells, tissues or organs in order to alleviate the lack of human transplants. The elimination of HEV from pigs, other animals and humans is consistent with the One Health concept, preventing subclinical infections in the animals as well as preventing transmission to humans and disease.

Cell culture systems for the study of hepatitis E virus

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

Roles of the genomic sequence surrounding the stem-loop structure in the junction region including the 3' terminus of open reading frame 1 in hepatitis E virus replication

Hepatitis E virus (HEV), a member of the family Hepeviridae, causes both acute and chronic viral hepatitis. We have previously demonstrated that the stem-loop structure in the junction region (JR) of HEV genome plays a critical role in HEV replication. However, the function of the sequence bordering the JR, including the 3' terminus of open reading frame (ORF1), in HEV replication is unknown. In this study, a panel of HEV Renilla luciferase (Rluc) replicons containing various deletions at 5' or 3' termini of the JR was constructed to determine the effect of the deletions on HEV replication in Huh7 human liver cells. We showed that even a single nucleotide deletion at the 5' terminus of the JR abolished HEV replication, whereas deletions at the 3' terminus of the JR also decreased virus replication efficiency. Furthermore, we also constructed firefly luciferase and Rluc dual-reporter HEV replicons containing the 3' terminal ORF1 of various lengths and the JR inserted upstream of the Rluc reporter. A higher level of HEV replication was observed in cells transfected with replicons containing the 3' terminal ORF1 than that of the JR only replicon. We also showed that the ORF3 noncoding sequence along with the JR promoted a higher level of translation activity than that promoted by JR and the ORF2 noncoding sequence.

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.

Detection and Characterization of Hepatitis E Virus in Goats at Slaughterhouse in Tai'an Region, China

Background

Hepatitis E virus (HEV) is a significant pathogen of viral hepatitis and can be transmitted through fecal-oral route. Epidemiological data concerning HEV in goats, however, are relatively sparse to date. Here, the prevalence and characteristics of HEV isolated from goats at slaughterhouse were investigated in Tai'an region, China.

Methods

Anti-HEV immunoglobulin G (IgG) in blood samples and HEV RNA in the liver samples were determined by using an enzyme-linked immunosorbent assay (ELISA) and a nested reverse transcription polymerase chain reaction (RT-PCR), respectively. In addition, partial nucleotide sequences of open reading frame 2 (ORF-2) of HEV isolates were analyzed.

Results

Fifty goat blood samples (46.7%, 50/120) were masculine for anti-HEV IgG. HEV RNA was detected in 2 liver samples (4.0%, 2/50) and belonged to genotype 4 subtype 4 h, with high identity (91.2-93%) with cow HEV strains detected in the same province, China.

Conclusions

These findings demonstrated that goats may be an important reservoir for HEV and can become a major source of HEV infection in humans via food chain.

Recent knowledge on hepatitis E virus in Suidae reservoirs and transmission routes to human

Hepatitis E virus (HEV) causes self-limiting acute hepatitis in humans that can eventually result in acute liver failures or progress to chronic infections. While in tropical and sub-tropical areas, HEV infections are associated with important waterborne epidemics, in Northern countries, HEV infections are autochthonous with a zoonotic origin. In the past decade, it has become clear that certain HEV genotypes are zoonotic and that swine, and more generally Suidae, are the main reservoir. Zoonotic transmissions of the virus may occur via direct contact with infected pigs, wild boars or consumption of contaminated meat. This review describes the current knowledge on domestic and wild Suidae as reservoirs of HEV and the evidence of the different routes of HEV transmission between these animals and humans.

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.

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.

Inactivation of Viruses and Bacteriophages as Models for Swine Hepatitis E Virus in Food Matrices

Hepatitis E virus has been recognised as a food-borne virus hazard in pork products, due to its zoonotic properties. This risk can be reduced by adequate treatment of the food to inactivate food-borne viruses. We used a spectrum of viruses and bacteriophages to evaluate the effect of three food treatments: high pressure processing (HPP), lactic acid (LA) and intense light pulse (ILP) treatments. On swine liver at 400 MPa for 10 min, HPP gave log₁₀ reductions of ≥4.2, ≥5.0 and 3.4 for feline calicivirus (FCV) 2280, FCV wildtype (wt) and murine norovirus 1 (MNV 1), respectively. Escherichia coli coliphage ϕX174 displayed a lower reduction of 1.1, while Escherichia coli coliphage MS2 was unaffected. For ham at 600 MPa, the corresponding reductions were 4.1, 4.4, 2.9, 1.7 and 1.3 log₁₀. LA treatment at 2.2 M gave log₁₀ reductions in the viral spectrum of 0.29-2.1 for swine liver and 0.87-3.1 for ham, with ϕX174 and MNV 1, respectively, as the most stable microorganisms. The ILP treatment gave log₁₀ reductions of 1.6-2.8 for swine liver, 0.97-2.2 for ham and 1.3-2.3 for sausage, at 15-60 J cm^-2, with MS2 as the most stable microorganism. The HPP treatment gave significantly (p < 0.05) greater virus reduction on swine liver than ham for the viruses at equivalent pressure/time combinations. For ILP treatment, reductions on swine liver were significantly (p < 0.05) greater than on ham for all microorganisms. The results presented here could be used in assessments of different strategies to protect consumers against virus contamination and in advice to food producers. Conservative model indicators for the pathogenic viruses could be suggested.

Hepatitis E virus in bottlenose dolphins Tursiops truncatus

Hepatitis E virus (HEV) infects several animal species that act as zoonotic reservoirs for viral transmission. Solid and liquid residues from infected animals could lead to HEV contamination of food and surface waters. Evidence of human HEV infection through ingestion of seafood (shellfish, mussels) has been reported. Dolphins generally feed on fish and squid but are able to adapt to an environment and consume whatever prey is available. Clinical signs of infected dolphins include lethargy, inappetence, behavioral aberrations and increased serum alanine aminotransferase (ALT). The dolphins examined in this study were maintained at the National Aquarium, Havana, Cuba. A total of 31 dolphins were evaluated for HEV markers. Sera were collected and screened for total immunoglobin (Ig) anti-HEV. Sera and liver homogenate were tested for HEV RNA by nested RT-PCR using primers targeting the open reading frame 1. Phylogenetic analysis was performed using partial nucleotide sequences at the amplified RNA-dependent RNA polymerase gene. Total anti-HEV Ig was detected in 32.2% (10 of 31), and 16.1% (5 of 31) of these dolphins were positive by both serology and HEV RNA testing. Nucleotide sequence analyses revealed that HEV strains identified in dolphins were genotype 3. This virus may represent an environmental contamination of food or wastewater as a source of HEV exposure and infection. Our findings provide evidence that HEV is associated with liver disorders in cetaceans and that it is advisable to screen for exposure of this virus in captive dolphins, particularly animals with elevated serum ALT or compromised liver function test results of undetermined cause.

Risk Profile of Hepatitis E Virus from Pigs or Pork in Canada

The role and importance of pigs and pork as sources of zoonotic hepatitis E virus (HEV) has been debated in Canada and abroad for over 20 years. To further investigate this question, we compiled data to populate a risk profile for HEV in pigs or pork in Canada. We organized the risk profile (RP) using the headings prescribed for a foodborne microbial risk assessment and used research synthesis methods and inputs wherever possible in populating the fields of this RP. A scoping review of potential public health risks of HEV, and two Canadian field surveys sampling finisher pigs, and retail pork chops and pork livers, provided inputs to inform this RP. We calculated summary estimates of prevalence using the Comprehensive Meta-analysis 3 software, employing the method of moments. Overall, we found the incidence of sporadic locally acquired hepatitis E in Canada, compiled from peer-reviewed literature or from diagnosis at the National Microbiology Laboratory to be low relative to other non-endemic countries. In contrast, we found the prevalence of detection of HEV RNA in pigs and retail pork livers, to be comparable to that reported in the USA and Europe. We drafted risk categories (high/medium/low) for acquiring clinical hepatitis E from exposure to pigs or pork in Canada and hypothesize that the proportion of the Canadian population at high risk from either exposure is relatively small.

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.

Molecular Biology and Infection of Hepatitis E Virus

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

Hepatitis E virus and the safety of plasma products: investigations into the reduction capacity of manufacturing processes

BACKGROUND

Hepatitis E virus (HEV) has been transmitted by transfusion of labile blood products and the occasional detection of HEV RNA in plasma pools indicates that HEV viremic donations might enter the manufacturing process of plasma products. To verify the safety margins of plasma products with respect to HEV, virus reduction steps commonly used in their manufacturing processes were investigated for their effectiveness to reduce HEV.

STUDY DESIGN AND METHODS

Detection methods for HEV removal (by reverse transcription quantitative polymerase chain reaction) and inactivation (using an infectivity assay) were established. Immunoaffinity chromatography and 20-nm virus filtration for Factor (F)VIII, cold ethanol fractionation, and low-pH treatment for immunoglobulin, heat treatment for human albumin, and 35-nm nanofiltration for FVIII inhibitor-bypassing activity (FEIBA) were investigated for their capacity to reduce HEV or the physicochemically similar viruses feline calicivirus (FCV) and hepatitis A virus (HAV).

RESULTS

For FVIII, HEV reduction of 3.9 and more than 3.9 log was demonstrated for immunoaffinity chromatography and 20-nm nanofiltration, respectively, and the cold ethanol fractionation for immunoglobulin removed more than 3.5 log of HEV, to below the limit of detection (LOD). Heat treatment of human albumin inactivated more than 3.1 log of HEV to below the LOD and 35-nm nanofiltration removed 4.0 log of HEV from the FEIBA intermediate. The results indicated HAV rather than FCV as the more relevant model virus for HEV.

CONCLUSION

Substantial HEV reduction during processes commonly used in the manufacturing of plasma products was demonstrated, similar to that previously demonstrated for HAV.

A Proline-Rich Domain in the Genotype 4 Hepatitis E Virus ORF3 C-Terminus Is Crucial for Downstream V105DLP108 Immunoactivity

The hepatitis E virus (HEV) is responsible for serious viral hepatitis worldwide. Animals are considered a reservoir of HEV, particularly pigs. While HEV infection in pigs and dogs is always asymptomatic, the virus causes high death rates in patients with pre-existing chronic liver disease and pregnant women in developing countries. HEV open reading frame 2 (ORF2) has been used as a diagnostic target to detect specific antibodies against HEV in serum samples. Recent research has additionally supported the potential utility of the ORF3 protein as a target in serum anti-HEV detection. However, the epitope distribution of ORF3 protein remains ambiguous. In the current study, we showed that continuous amino acid motif, VDLP, at the C-terminus of genotype 4 HEV ORF3 is a core sequence of the ORF3 protein epitope. Moreover, cooperative interaction with upstream elements is essential for its immunoactivity. Three proline residues (P99, P102 and P103) in the upstream proline-rich domain exerted significant effects on the immunocompetence of VDLP. ELISA results revealed that SAPPLPPVVDLP and SAPPLPPVVDLPQLGL peptides containing the identified VDLP epitope display weaker reactions with anti-HEV serum than the commercial ELISA kit. Our collective findings provide valuable information on the epitope distribution characteristics of HEV ORF3 and improve our understanding of the influence of the proline-rich domain on the immunoactivity of downstream amino acids in the C-terminal region.

Pregnancy serum facilitates hepatitis E virus replication in vitro

Hepatitis E virus (HEV) infection causes high mortality in pregnant women. However, the pathogenic mechanisms of HEV infection in pregnant women remain unknown. In this study, the roles of pregnancy serum in HEV infection were investigated using an efficient cell culture system. HEV infection was exacerbated by supplementing with pregnancy serum, especially theat in third trimester of pregnancy. Oestrogen receptors (ER-α and ER-β) were activated in cells supplemented with pregnancy serum and were significantly inhibited during HEV infection. Type I IFN, especially IFN-β, showed delayed upregulation in HEV-infected cells supplemented with the serum in the third trimester of pregnancy, which indicated that delayed IFN-β expression may facilitate viral replication. Results suggested that pregnancy serum accelerated HEV replication by suppressing oestrogen receptors and type I IFN in the early stage of infection.

Mode of swine hepatitis E virus infection and replication in primary human hepatocytes

The aim of this study was to investigate the infection and replication of swine-derived hepatitis E virus (HEV) in primary cultured human hepatocytes (PHCs). Hepatocytes were cultured from the resected normal livers of patients with metastatic tumours. These cultured hepatocytes were infected with swine-derived genotype 3 or 4 HEV. Viral replication was monitored using reverse transcriptase-quantitative PCR. The amount of HEV RNA increased in the culture media and cells following infection. Immunofluorescence staining implied that the spread of HEV infection in hepatocytes was attributed mainly to cell-to-cell transmission via the cell membrane. The sequences of the inoculated and propagated HEV were determined to examine whether sequence variation occurred during infection. Sequence analysis showed that there were no differences between inoculated and propagated HEV, demonstrating that in vitro infection and replication of swine HEV in PHCs occurred without sequence variation.

Characterization of sporadic acute hepatitis E and comparison of hepatitis E virus genomes in acute hepatitis patients and pig liver sold as food in Mie, Japan

AIM

To characterize hepatitis E in Mie prefecture and to investigate whether raw pig liver sold as food in Mie is contaminated with hepatitis E virus (HEV) strains similar to those recovered from patients.

METHODS

Seventeen patients with sporadic acute hepatitis E treated from 2004 to 2012 were studied. A total of 243 packages of raw pig liver from regional grocery stores were tested for the presence of HEV RNA. The partial genomic sequences of human and swine HEV isolates were determined and subjected to the phylogenetic analyses.

RESULTS

The HEV isolates recovered from the 17 patients segregated into genotype 3 (n = 15) and genotype 4 (n = 2), and 15 genotype 3 isolates further segregated into 3e (n = 11) and 3b (n = 4). Pig liver specimens from 12 (4.9%) of the 243 packages had detectable HEV RNA. All 12 swine HEV isolates were grouped into genotype 3 (3a or 3b). Although no 3e strains were isolated from pig liver specimens, two 3b swine strains were 99.5-100% identical to two HEV strains recovered from hepatitis patients, within 412-nt partial sequences.

CONCLUSION

The 3e HEV was prevalent among hepatitis E patients. HEV RNA was detected in approximately 5% of pig liver sold as food. The presence of identical HEV strains between hepatitis patients and pig liver indicated that pigs play an important role as reservoirs for HEV in humans in Mie. Further studies are needed to clarify the source of 3e HEV in the animal and environmental reservoirs.

Current epidemiology of hepatitis E virus infection in the United States: low seroprevalence in the National Health and Nutrition Evaluation Survey

Analysis of the National Health and Nutrition Evaluation Survey (NHANES) 1988-1994 dataset found a relatively high seroprevalence (21%) of hepatitis E virus (HEV) infection in the U.S. general population. Using data obtained within the NHANES 2009-2010 survey, where a high performance assay for HEV was used, we estimated the weighted seroprevalence of HEV infection among U.S. individuals 6 years and older. We also evaluated factors associated with HEV seropositivity. A total of 8,814 individuals were included in the analysis. The median age of study participants was 37 years (interquartile range [IQR] 17-58 years), with 51.2% being female. The weighted national seroprevalence of HEV was 6% (95% confidence interval [CI] 5.1%-6.9%). About 0.5% of those with HEV had evidence of recent exposure (immunoglobulin M-positive). In the univariate analyses, factors associated with HEV seropositivity were increasing age (P-trend<0.001), birth outside of the U.S., Hispanic race, and "meat" consumption (>10 times/month). No significant association was observed with low socioeconomic status, water source, or level of education. In the multivariate analysis, only older age remained predictive of HEV seropositivity.

CONCLUSION

The weighted national seroprevalence of HEV in the U.S. is much less than previously reported. Using data obtained with a high performance assay, the seroprevalence of HEV was estimated at 6.0% in the U.S. Based on these results, the seroprevalence of HEV is only one-third as high as previously reported.

Hepatitis E genotype 4 virus from feces of monkeys infected experimentally can be cultured in PLC/PRF/5 cells and upregulate host interferon-inducible genes

The understanding of the interaction between hepatitis E virus (HEV) and its host cells has been impeded greatly by the absence of a cell culture system. In this study, an efficient cultivation method was developed in PLC/PRF/5 cells for HEV genotype 4 from the feces of monkeys infected experimentally. Compared to minimal essential medium (MEM), mixed Dulbecco's Modified Eagle's Medium (DMEM)/M199 improved the infection efficiency of HEV in PLC/PRF/5 cells. The incubation time and temperature were set at 6 hr and 40°C, respectively. Compared to a 100% ELISA positive ratio (EPR) of 1 × 10(6)  copies/ml HEV inoculated flasks, the ELISA positive ratio was 100%, 75%, 37.5%, and 100% for flasks inoculated with HEV incubated for 30 min under the conditions of pH 3.0, pH 11.0, 56°C and delipidation treatment, respectively. Gene expression profiles of HEV inoculated and control PLC/PRF/5 cells were assayed using a microarray. Four interferon-inducible genes, IFI27, IFI6, Mx1, and CMPK2, were up-regulated during HEV-infection. Furthermore, the replication of HEV was inhibited at 3-14 days after treatment with 500 IU/ml IFN-α2b.

High genomic similarity between European type hepatitis E virus subgenotype 3e strains isolated from an acute hepatitis patient and a wild boar in Mie, Japan

A 67-year-old male living in Tsu city, Mie prefecture, Japan was referred to our hospital for further examination of acute liver injury and was diagnosed as having clinical hepatitis E virus (HEV) infection in January 2010. The HEV strain (HE-JA11-1701) isolated from the patient belonged to genotype 3 and European-type subgenotype 3e. It was presumed that the patient had been infected from a wild boar (Sus scrofa leucomystax) because he consumed meat/viscera from a wild boar that he had captured himself as a hunter approximately 2 months before disease onset. A specimen of the boar meat/viscera that the patient had ingested was not available. However, the HE-JA11-1701 strain was 99.8% identical within the 412-nucleotide sequence of the open reading frame 2 region to a HEV strain (JBOAR012-Mie08) that had been recovered from a wild boar captured near the patient's hunting area in 2008. A phylogenetic analysis confirmed that the two HEV strains had a close genetic relationship and were segregated into subgenotype 3e, supported by a high bootstrap value of 99%. Of note, the HE-JA11-1701 and JBOAR012-Mie08 strains were remotely related to the 3e strains reported in Japan and European countries, with a nucleotide difference of 7.9-13.9%, reinforcing the uniqueness of the 3e strains obtained in the present study. These results strongly support our speculation that the patient developed acute hepatitis E via consumption of HEV-infected boar meat/viscera. Genetic analyses of HEV strains are useful for tracing infectious sources in sporadic cases of acute hepatitis E.

An ORF1-rearranged hepatitis E virus derived from a chronically infected patient efficiently replicates in cell culture

Hepatitis E is an increasingly reported disease in industrialized countries. Studies on the replication cycle of hepatitis E virus (HEV) are hampered due to the lack of efficient and robust cell culture systems for this virus. We describe the successful isolation of HEV derived from a chronically infected kidney transplant patient held under immunosuppressive therapy. Inoculation of serum sample 47832 onto the human lung carcinoma cell line A549 resulted in the replication of the virus as shown by RT-qPCR. This novel human-derived HEV strain is closely related to a wild boar-derived genotype 3 strain, which did not replicate in A549 cells. It carries a 186 nucleotide insertion in the hypervariable ORF1-region, derived from two parts of its ORF1. By passaging of the infected cells, a cell line continuously producing HEV particles was generated as demonstrated by RT-qPCR, immuno-electron microscopy, density gradient centrifugation and immunohistochemistry. Replication of the produced virus was demonstrated after its inoculation onto fresh A549 cells and two consecutive passages, whereas heating at 65 °C for 2 min abolished its infectivity. Several point mutations scattered along the whole genome were present in the HEV strain from the second passage; however, the ORF1 insertion was still present. Previously, cell culture isolation of two other HEV strains carrying insertions in their hypervariable regions, but originating from human ribosomal protein genes, has been described. The findings may indicate that cell culture adaptation of is mostly dependent on the length and position of the insertion, rather than from the sequence itself.

Genetic host specificity of hepatitis E virus

Hepatitis E virus (HEV) causes epidemic and sporadic cases of hepatitis worldwide. HEV genotypes 3 (HEV3) and 4 (HEV4) infect humans and animals, with swine being the primary reservoir. The relevance of HEV genetic diversity to host adaptation is poorly understood. We employed a Bayesian network (BN) analysis of HEV3 and HEV4 to detect epistatic connectivity among protein sites and its association with the host specificity in each genotype. The data imply coevolution among ∼70% of polymorphic sites from all HEV proteins and association of numerous coevolving sites with adaptation to swine or humans. BN models for individual proteins and domains of the nonstructural polyprotein detected the host origin of HEV strains with accuracy of 74-93% and 63-87%, respectively. These findings, taken together with lack of phylogenetic association to host, suggest that the HEV host specificity is a heritable and convergent phenotypic trait achievable through variety of genetic pathways (abundance), and explain a broad host range for HEV3 and HEV4.

Features of hepatitis E virus infection in humans and animals in Japan

In Japan, hepatitis E had long been considered to be a rare liver disease which can be accidentally imported from endemic countries in Asia and Africa, where the sanitation conditions are suboptimal. However, since the identification of the first autochthonous hepatitis E case and hepatitis E viremic domestic pigs in Japan in 2001, our understanding of hepatitis E virus (HEV) infection in this country has been changing markedly. This has largely been due to the development of serological and gene-based diagnostic assays, the accumulation of molecular epidemiological findings on HEV infection in humans and animals (as potential reservoirs for HEV in humans) and the recognition of the importance of zoonotic food-borne and other routes of transmission of HEV, including blood-borne transmission. Although it is now evident that autochthonous hepatitis E in Japan is far more common than was previously thought, clinical and subclinical HEV infections indigenous to Japan remain underdiagnosed and their prevalence is still underestimated due to the presence of unknown transmission routes and a low awareness of the infection status by many physicians in Japan. This review focuses on the features of HEV infection in humans and animals, as definitive or potential reservoirs for HEV, in Japan, and updates the current knowledge on the routes of transmission, including zoonotic routes, which are important for the maintenance and spread of HEV in Japan.

Culture systems for hepatitis E virus

The lack of an efficient cell culture system for hepatitis E virus (HEV) has greatly hampered detailed analyses of this virus. The first efficient cell culture systems for HEV that were developed were capable of secreting infectious HEV progenies in high titers into culture media, using PLC/PRF/5 cells derived from human hepatocellular carcinoma and A549 cells derived from human lung cancer as host cells. The success achieved with the original genotype 3 JE03-1760F strain has now been extended to various HEV strains in fecal and serum samples obtained from hepatitis E patients and to HEV strains in fecal and serum samples and liver tissues obtained from pigs and wild boar across species barriers. In addition, infectious HEV cDNA clones of the wild-type JE03-1760F strain and its variants have been engineered. Cell culture-generated HEV particles and those in circulating blood were found to be associated with lipids and open reading frame 3 (ORF3) protein, thereby likely contributing to the assembly and release of HEV from infected cells both in vivo and in vitro. The ORF3 protein interacts with the tumor susceptibility gene 101, a critical cellular protein required for the budding of enveloped viruses, through the Pro, Ser, Ala, and Pro (PSAP) motif in infected cells; ORF3 is co-localized with multivesicular bodies (MVBs) in the cytoplasm of infected cells, thus suggesting that HEV requires the MVB pathway for the egress of virus particles. This article reviews the development of efficient cell culture systems for a wide variety of infectious HEV strains obtained from humans, pigs, and wild boar, and also provides details of a new model for virion egress.

Molecular analysis of hepatitis E virus from farm rabbits in Inner Mongolia, China and its successful propagation in A549 and PLC/PRF/5 cells

Rabbit hepatitis E virus (HEV) strains have recently been isolated in several areas of China and in the US and France. However, the host range, distribution and zoonotic potential of these HEV strains remain unknown and their propagation in cultured cells has not yet been reported. A total of 211 4-month-old rabbits raised on a farm in Inner Mongolia were tested for the presence of anti-HEV antibodies and HEV RNA. Overall, 121 rabbits (57.3%) tested positive for anti-HEV antibodies, and 151 (71.6%) had detectable HEV RNA. The 174 HEV strains recovered from these viremic rabbits, including two distinct strains each from 23 rabbits, differed from each other by up to 13.6% in a 412-nucleotide (nt) sequence within ORF2, and were 89.3-95.9% identical to the reported rabbit HEV strains in other provinces of China. Three representative Inner Mongolian strains, one each from three phylogenetic clusters, whose entire genomic sequences were determined, shared 79.6-96.7% identities with reported rabbit HEV strains within the entire or 242- to 1349-nt partial genomic sequence. Rabbit HEV strains recovered from liver tissues of rabbits with a high HEV load propagated efficiently in human cell lines (A549 and PLC/PRF/5 cells), suggesting the potential zoonotic risk of rabbit HEV.