Hepatitis E virus in rats, Los Angeles, California, USA

The Current Host Range of Hepatitis E Viruses

Hepatitis E virus (HEV) is an emerging zoonotic pathogen transmitting both human to human via the fecal oral route and from animals to humans through feces, direct contact, and consumption of contaminated meat products. Understanding the host range of the virus is critical for determining where potential threats to human health may be emerging from and where potential reservoirs for viral persistence in the environment may be hiding. Initially thought to be a human specific disease endemic to developing countries, the identification of swine as a primary host for genotypes 3 and 4 HEV in industrialized countries has begun a long journey of discovering novel strains of HEV and their animal hosts. As we continue identifying new strains of HEV in disparate animal species, it is becoming abundantly clear that HEV has a broad host range and many of these HEV strains can cross between differing animal species. These cross-species transmitting strains pose many unique challenges to human health as they are often unrecognized as sources of viral transmission.

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

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

Comparative Pathology of Hepatitis A Virus and Hepatitis E Virus Infection

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

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.

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

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

Hepatitis E Virus: Animal Models and Zoonosis

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

Detection of rat hepatitis E virus, but not human pathogenic hepatitis E virus genotype 1-4 infections in wild rats from Lithuania

Rat hepatitis E virus (HEV) is an orthohepevirus which is related to other HEV found in humans and other mammals. It was first identified in Norway rats (Rattus norvegicus) from Germany in 2010, and later it has been detected in Black rats (Rattus rattus) and Norway rats from USA, China, Indonesia, Vietnam and many European countries. In this study, we describe molecular and serological investigations of Black and Norway rats trapped in Lithuania, Eastern Europe, for infections with rat HEV and human HEV genotypes 1-4. Rat HEV-specific real-time reverse transcription-PCR (RT-qPCR) analysis of rat liver samples revealed the presence of rat HEV in 9 of 109 (8.3%) samples. In contrast, a RT-qPCR specific for HEV genotypes 1-4 did not reveal any positive samples. A nested broad spectrum RT-PCR was used for a confirmation of rat HEV infection with a subsequent sequencing of the amplified rat HEV genome fragment. Phylogenetic analysis revealed a clustering of all newly identified rat HEV sequences with Norway rat-derived rat HEV sequences from Germany within the species Orthohepevirus C. An indirect ELISA using a yeast-expressed truncated rat HEV capsid protein variant revealed 31.2% seropositive samples indicating a high rate of rat HEV circulation in the rat population examined. In conclusion, the current investigation confirms rat HEV infections in Norway and Black rats in Lithuania, Eastern Europe, and the non-persistent nature of HEV infection.

Novel orthohepeviruses in wild rodents from São Paulo State, Brazil

The Hepeviridae comprise single-stranded positive-sense RNA viruses classified into two genera, Orthohepevirus and Piscihepevirus. Orthohepeviruses have a wide host range that includes rodents, but previous studies had been restricted to rodents of the Muridae family. In this study, we applied a high-throughput sequencing approach to examine the presence of orthohepeviruses in rodents from São Paulo State, Brazil. We also used RT-PCR to determine the frequency of orthohepeviruses in our sampled population. We identified novel orthohepeviruses in blood samples derived from Necromys lasiurus (1.19%) and Calomys tener (3.66%). Therefore, our results expand the host range and viral diversity of the Hepeviridae family.

Chevrier's Field Mouse (Apodemus chevrieri) and Père David's Vole (Eothenomys melanogaster) in China Carry Orthohepeviruses that form Two Putative Novel Genotypes Within the Species Orthohepevirus C

Hepatitis E virus (HEV) is the prototype of the family Hepeviridae and the causative agent of common acute viral hepatitis. Genetically diverse HEV-related viruses have been detected in a variety of mammals and some of them may have zoonotic potential. In this study, we tested 278 specimens collected from seven wild small mammal species in Yunnan province, China, for the presence and prevalence of orthohepevirus by broad-spectrum reverse transcription (RT)-PCR. HEV-related sequences were detected in two rodent species, including Chevrier's field mouse (Apodemus chevrieri, family Muridae) and Père David's vole (Eothenomys melanogaster, family Cricetidae), with the infection rates of 29.20% (59/202) and 7.27% (4/55), respectively. Further four representative full-length genomes were generated: two each from Chevrier's field mouse (named RdHEVAc14 and RdHEVAc86) and Père David's vole (RdHEVEm40 and RdHEVEm67). Phylogenetic analyses and pairwise distance comparisons of whole genome sequences and amino acid sequences of the gene coding regions showed that orthohepeviruses identified in Chinese Chevrier's field mouse and Père David's vole belonged to the species Orthohepevirus C but were highly divergent from the two assigned genotypes: HEV-C1 derived from rat and shrew, and HEV-C2 derived from ferret and possibly mink. Quantitative real-time RT-PCR demonstrated that these newly discovered orthohepeviruses had hepatic tropism. In summary, our work discovered two putative novel genotypes orthohepeviruses preliminarily named HEV-C3 and HEV-C4 within the species Orthohepevirus C, which expands our understanding of orthohepevirus infection in the order Rodentia and gives new insights into the origin, evolution, and host range of orthohepevirus.

Detection and Characterization of Homologues of Human Hepatitis Viruses and Pegiviruses in Rodents and Bats in Vietnam

Rodents and bats are now widely recognised as important sources of zoonotic virus infections in other mammals, including humans. Numerous surveys have expanded our knowledge of diverse viruses in a range of rodent and bat species, including their origins, evolution, and range of hosts. In this study of pegivirus and human hepatitis-related viruses, liver and serum samples from Vietnamese rodents and bats were examined by PCR and sequencing. Nucleic acids homologous to human hepatitis B, C, E viruses were detected in liver samples of 2 (1.3%) of 157 bats, 38 (8.1%), and 14 (3%) of 470 rodents, respectively. Hepacivirus-like viruses were frequently detected (42.7%) in the bamboo rat, Rhizomys pruinosus, while pegivirus RNA was only evident in 2 (0.3%) of 638 rodent serum samples. Complete or near-complete genome sequences of HBV, HEV and pegivirus homologues closely resembled those previously reported from rodents and bats. However, complete coding region sequences of the rodent hepacivirus-like viruses substantially diverged from all of the currently classified variants and potentially represent a new species in the Hepacivirus genus. Of the viruses identified, their routes of transmission and potential to establish zoonoses remain to be determined.

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.

Diseases Transmitted by Man's Worst Friend: the Rat

Historically, the rat has been considered a scourge to mankind, for example, rats infected with the plague bacillus that caused the Black Death, which accounted for millions of deaths in Europe during the Middle Ages. At least three pandemics (in the 5th and 6th, 8th through 14th, and 19th through 21st centuries) of plague ravaged civilizations, and the disease undoubtedly plagued humankind prior to recorded history. Also, numerous other diseases are spread to humans by rats; thus, a quote from Hans Zinsser's text Rats, Lice, and History, "Man and rat will always be pitted against each other as implacable enemies," conveys the general revulsion that society holds for the wild rat.

Serological evidence of hepatitis E virus infection in zoo animals and identification of a rodent-borne strain in a Syrian brown bear

Hepatitis E virus (HEV) is the causative agent of hepatitis E, an emerging infectious disease of humans. HEV infections have also been described in various animal species. Whereas domestic pigs and wild boars are well-known animal reservoirs for HEV, the knowledge on natural HEV infection in zoo animals is scarce so far. Here, we analysed 244 sera from 66 mammal species derived from three zoos in Germany using a commercial double antigen sandwich ELISA. HEV-specific antibodies were detected in 16 animal species, with the highest detection rates in suids (33.3%) and carnivores (27.0%). However, RNA of the human pathogenic HEV genotypes 1-4 was not detected in the serum samples from suids or carnivores. Using a broad spectrum RT-PCR, a ratHEV-related sequence was identified in a sample of a female Syrian brown bear (Ursus arctos syriacus). Subsequent serum samples within a period of five years confirmed a HEV seroconversion in this animal. No symptoms of hepatitis were recorded. In a follow-up investigation at the same location, closely related ratHEV sequences were identified in free-living Norway rats (Rattus norvegicus), whereas feeder rats (Rattus norvegicus forma domestica) were negative for HEV-specific antibodies and RNA. Therefore, a spillover infection of ratHEV from free-living Norway rats is most likely. The results indicate that a wide range of zoo animals can be naturally infected with HEV or HEV-related viruses. Their distinct role as possible reservoir animals for HEV and sources of HEV infection for humans and other animals remains to be investigated.

Hepatitis E virus and related viruses in wild, domestic and zoo animals: A review

Hepatitis E is a human disease mainly characterized by acute liver illness, which is caused by infection with the hepatitis E virus (HEV). Large hepatitis E outbreaks have been described in developing countries; however, the disease is also increasingly recognized in industrialized countries. Mortality rates up to 25% have been described for pregnant women during outbreaks in developing countries. In addition, chronic disease courses could be observed in immunocompromised transplant patients. Whereas the HEV genotypes 1 and 2 are mainly confined to humans, genotypes 3 and 4 are also found in animals and can be zoonotically transmitted to humans. Domestic pig and wild boar represent the most important reservoirs for these genotypes. A distinct subtype of genotype 3 has been repeatedly detected in rabbits and a few human patients. Recently, HEV genotype 7 has been identified in dromedary camels and in an immunocompromised transplant patient. The reservoir animals get infected with HEV without showing any clinical symptoms. Besides these well-known animal reservoirs, HEV-specific antibodies and/or the genome of HEV or HEV-related viruses have also been detected in many other animal species, including primates, other mammals and birds. In particular, genotypes 3 and 4 infections are documented in many domestic, wildlife and zoo animal species. In most cases, the presence of HEV in these animals can be explained by spillover infections, but a risk of virus transmission through contact with humans cannot be excluded. This review gives a general overview on the transmission pathways of HEV to humans. It particularly focuses on reported serological and molecular evidence of infections in wild, domestic and zoo animals with HEV or HEV-related viruses. The role of these animals for transmission of HEV to humans and other animals is discussed.

Animal Models for Hepatitis E Virus

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

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.

Emerging Foodborne and Agriculture-Related Viruses

Viruses rapidly evolve and can emerge in unpredictable ways. Transmission pathways by which foodborne viruses may enter human populations and evolutionary mechanisms by which viruses can become virulent are discussed in this chapter. A majority of viruses emerge from zoonotic animal reservoirs, often by adapting and infecting intermediate hosts, such as domestic animals and livestock. Viruses that are known foodborne threats include hepatitis E virus, tick-borne encephalitis virus, enteroviruses, adenovirus, and astroviruses, among others. Viruses may potentially evolve and emerge as a result of modern agricultural practices which can concentrate livestock and bring them into contact with wild animals. Examples of viruses that have emerged in this manner are influenza, coronaviruses such as severe acute respiratory syndrome and Middle East respiratory syndrome, and the Nipah virus. The role of bats, bush meat, rodents, pigs, cattle, and poultry as reservoirs from which infectious pathogenic viruses emerge are discussed.

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

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

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.

Rabbit hepatitis E virus is an opportunistic pathogen in specific-pathogen-free rabbits with the capability of cross-species transmission

Hepatitis E virus (HEV) has been detected in rabbits, a recently identified natural reservoir. In this study, anti-HEV antibodies and viral RNA were detected in rabbits sourced from a specific-pathogen-free (SPF) rabbit vendor in Shaanxi Province, China. BLAST results of partial HEV ORF2 genes cloned here indicated that two viral strains circulated in the rabbits. Sequence determination of the complete genome (7302bp) of one strain and a partial ORF1 gene (1537bp) of the other strain showed that they shared 90% identity with one another and 78%-94% identity with other known rabbit HEVs. In addition, inoculation with rabbit HEV from SPF rabbits studied here resulted in infection of SPF pigs; this cross-species transmission was evidenced by seroconversion, viremia and faecal virus shedding. These results suggest that to prevent spread of this zoonotic pathogen, rabbits should be tested routinely for HEV RNA in SPF vendor facilities.

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

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

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.

Hepatitis E: Discovery, global impact, control and cure

Hepatitis E was identified as an epidemic of non-A, non-B hepatitis from Kashmir, India in 1978. Hepatitis E virus (HEV), the etiological agent is the sole member of family Hepeviridae. The virus has marked heterogeneity and infects many animals like bats, camel, chicken, deer, boar, mongoose, pigs, rats, rabbit and cutthroat trout. Hepatitis E is a disease with a major global impact and has two distinct epidemiological patterns. Hepatitis E is an imperative health issue in developing nations, transmitted through sullied water and happens most every now in young adults. The disease is particularly severe during pregnancy and in people with underlying liver cirrhosis. Autochthonous hepatitis E is increasingly recognized in developed countries. The virus infects domestic pigs, wild boar and Sika deer in these countries. HEV infections in humans occur by eating the undercooked game flesh, raw liver from supermarkets and Figatelli sausages. Blood transfusion-associated HEV infections occur in many countries and screening of donors for HEV RNA is under consideration. Hepatitis E causes a number of extrahepatic diseases, including a wide spectrum of neurological syndromes. HEV genotype 3 causes prolonged viremia, chronic hepatitis, liver fibrosis and cirrhosis in organ transplant patients. The virus is amenable to ribavirin monotherapy and most patients clear the virus in a few weeks. Hepatitis E vaccine -239, marketed in China, has shown high efficacy with sustained protection for over four years.

Serological evidence of infection with rodent-borne hepatitis E virus HEV-C1 or antigenically related virus in humans

Zoonotic potential of a rat-derived hepatitis E virus (HEV), designated as HEV-C1, remains unknown. To evaluate the risk for HEV-C1 infection in humans, paired sera of 208 hospitalized febrile patients collected from 2001 to 2003 in Hanoi, Vietnam, were examined for IgG antibodies to HEV-C1 and genotype 1 HEV (HEV-1), which is common in humans. IgG antibodies to virus-like particles (VLPs) of HEV-C1 and/or HEV-1 were detected from 99 of the 208 convalescent sera in enzyme-linked immunosorbent assay (ELISA). IgG antibody titers to HEV-C1 antigen in 3 of the 99 sera were more than 8-fold higher than those to HEV-1 antigen. IgM antibodies to HEV-C1 antigen were detected in acute sera from 2 of the 3 patients in ELISA and Western blotting. However, no HEV genome was detected. Clinical information was available for 1 of the 2 patients. Hepatic enzymes, aspartate aminotransferase and alanine aminotransferase, were mildly elevated (156 IU/l and 68 IU/l, respectively), and hepatomegaly was detected by ultrasonography. The patient recovered from the illness after 17 days. These results indicated that HEV-C1 or its variants infect humans in Vietnam and may cause acute febrile illness with mild liver dysfunction.

Hepatitis E Pathogenesis

Although most hepatitis E virus (HEV) infections are asymptomatic, some can be severe, causing fulminant hepatitis and extra-hepatic manifestations, including neurological and kidney injuries. Chronic HEV infections may also occur in immunocompromised patients. This review describes how our understanding of the pathogenesis of HEV infection has progressed in recent years.

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

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

Aboriginal and invasive rats of genus Rattus as hosts of infectious agents

From the perspective of ecology of zoonotic pathogens, the role of the Old World rats of the genus Rattus is exceptional. The review analyzes specific characteristics of rats that contribute to their important role in hosting pathogens, such as host-pathogen relations and rates of rat-borne infections, taxonomy, ecology, and essential factors. Specifically the review addresses recent taxonomic revisions within the genus Rattus that resulted from applications of new genetic tools in understanding relationships between the Old World rats and the infectious agents that they carry. Among the numerous species within the genus Rattus, only three species-the Norway rat (R. norvegicus), the black or roof rat (R. rattus), and the Asian black rat (R. tanezumi)-have colonized urban ecosystems globally for a historically long period of time. The fourth invasive species, R. exulans, is limited to tropical Asia-Pacific areas. One of the points highlighted in this review is the necessity to discriminate the roles played by rats as pathogen reservoirs within the land of their original diversification and in regions where only one or few rat species were introduced during the recent human history.

Therapeutic targets for the treatment of hepatitis E virus infection

INTRODUCTION

Hepatitis E virus (HEV) is one of the most common causes of acute viral hepatitis in the world with an estimated 20 million infections per year. Although the mortality rate is < 1% among the general population, pregnant women can have a fatality rate of up to 30%. Additionally, chronic hepatitis E has increasingly become a significant clinical problem in immunocompromised individuals. Effective antivirals against HEV are needed.

AREAS COVERED

This review article addresses the current state of knowledge of HEV infections with regard to animal and cell culture model systems that are important for antiviral discovery and testing, our current understanding of the molecular mechanisms of virus replication, our understanding of how each viral protein functions, and areas that can potentially be exploited as therapeutic targets.

EXPERT OPINION

Lack of an efficient cell culture system for HEV propagation, the limited knowledge of HEV lifecycle, and the inherent self-limiting infection within the normal populace make the development of new therapeutic agents against HEV challenging. There are many promising therapeutic targets, and the tools for identifying and testing potential antivirals are rapidly evolving. The development of effective therapeutics against HEV in immunocompromised and pregnant patient populations is warranted.

Molecular detection of hepatitis E virus in sheep from southern Xinjiang, China

Hepatitis E virus (HEV) is a causative agent of infectious hepatitis in animals and humans both in developing and developed countries. Here, we collected 500 sheep sera and 75 raw sheep liver samples from a slaughterhouse in the southern part of the Xinjiang region, China, along with 26 sera of butchers from the same slaughterhouse. All serum samples were tested for anti-HEV antibody by enzyme-linked immunosorbent assay. Both serum and liver samples were evaluated for the presence of HEV RNA by nested polymerase chain reaction targeting partial nucleotide sequences of open reading frame 2 (ORF2). The results indicate that sheep seroprevalence was 35.20 % (176/500) and that four of the 75 (5.3 %) sheep livers showed detectable amounts of HEV RNA. The seroprevalence of the butchers was 57.7 % (15/26). The four amplicons shared 97.8-100 % nucleotide sequence identity and had pairwise sequence identities of 81.6-85.3 %, 84.2-85.3 %, 82.1-85.3 % and 84.7-97.9 % with the corresponding regions of genotypes 1, 2, 3 and 4 of HEV, respectively. A phylogenetic tree was constructed based on alignments of an amplified 186-bp ORF2 sequence and corresponding reference strains. The analysis showed that the four sheep strains detected in our study formed a lineage within a genotype 4 cluster that contains hb-3, bjsw1, T1, swCH189 and swCH25, all of which belong to genotype 4, subtype 4d. The results indicated a high level of seroconversion in sheep and suggested that sheep liver may be a source of foodborne HEV infection in humans.

Hepatitis E Virus and Related Viruses in Animals

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

Characterization of Two Novel Linear B-Cell Epitopes in the Capsid Protein of Avian Hepatitis E Virus (HEV) That Are Common to Avian, Swine, and Human HEVs

Antisera raised against the avian hepatitis E virus (HEV) capsid protein are cross-reactive with human and swine HEV capsid proteins. In this study, two monoclonal antibodies (MAbs) against the avian HEV capsid protein, namely, 3E8 and 1B5, were shown to cross-react with the swine HEV capsid protein. The motifs involved in binding both MAbs were identified and characterized using phage display biopanning, peptide synthesis, and truncated or mutated protein expression, along with indirect enzyme-linked immunosorbent assay (ELISA) and Western blotting. The results showed that the I/VPHD motif is a necessary core sequence and that P and H are two key amino acids for recognition by MAb 3E8. The VKLYM/TS motif is the minimal amino acid sequence necessary for recognition by MAb 1B5. Cross-reactivity between the two epitopes and antibodies against avian, swine, and human HEVs in sera showed that both epitopes are common to avian, swine, and human HEVs. In addition, amino acid sequence alignment of the capsid proteins revealed that the key motifs of both novel epitopes are the same in HEVs from different animal species, predicting that they may be common to HEV isolates from boars, rabbits, rats, ferrets, mongooses, deer, and camels as well. Protein modeling analysis showed that both epitopes are at least partially exposed on the surface of the HEV capsid protein. Protective capacity analysis demonstrated that the two epitopes are nonprotective against avian HEV infection in chickens. Collectively, these studies characterize two novel linear B-cell epitopes common to avian, swine, and human HEVs, which furthers the understanding of HEV capsid protein antigenic structure.

IMPORTANCE

More and more evidence indicates that the host range diversity of hepatitis E virus (HEV) is a global public health concern. A better understanding of the antigenic structure of the HEV capsid protein may improve disease diagnosis and prevention. In this study, binding site mapping and localization as well as the antigenic biology of two novel linear B-cell epitopes common to several different species of HEV were characterized. These findings partially reveal the antigenic structure of the HEV capsid protein and provide potential applications for the development of diagnostics and interventions for HEV 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.

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

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

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.

Zoonotic origin of hepatitis E

The concept of zoonotic viral hepatitis E has emerged a few years ago following the discovery of animal strains of hepatitis E virus (HEV), closely related to human HEV, in countries where sporadic cases of hepatitis E were autochthonous. Recent advances in the identification of animal reservoirs of HEV have confirmed that strains circulating in domestic and wild pigs are genetically related to strains identified in indigenous human cases. The demonstration of HEV contamination in the food chain or pork products has indicated that HEV is frequently a foodborne zoonotic pathogen. Direct contacts with infected animals, consumption of contaminated animal meat or meat products are all potential means of zoonotic HEV transmission. The recent identification of numerous other genetically diverse HEV strains from various animal species poses additional potential concerns for HEV zoonotic infection.

Hepatitis E virus in developed countries: one of the most successful zoonotic viral diseases in human history?

Until recently, hepatitis E was thought to be largely confined to hyperendemic areas in Asia, Africa and Mexico. Over the last 10 years it has become clear that this is not the case, as it is surprisingly common in developed countries. In these settings, it is caused by HEV genotypes 3 and 4, and is a porcine zoonosis. It causes a range of human illness including acute and chronic hepatitis, and a spectrum of neurological injury. HEV RNA has been found in donated blood from an increasing number of countries, and in some locations with a very high incidence. The clinical phenotype and burden of disease in humans is still emerging. In contrast to previous 'received wisdom', zoonotically transmitted HEV may be one of the most successful zoonotic viral infections in human history. How did we, as a scientific community, get this so badly wrong? This review considers this question from a largely clinical perspective, explores the places HEV has been 'hiding' and the emerging clinical phenotype in humans.

Complete genome sequence of a rat hepatitis e virus strain isolated in the United States

Hepatitis E virus is a common cause of acute hepatitis in humans. Related viruses have been isolated from multiple animal species, including rats, but their impact on human health is unclear. We present the first full-length genome sequence of a rat hepatitis E virus strain isolated in the United States (LA-B350).

Rat sightings in New York City are associated with neighborhood sociodemographics, housing characteristics, and proximity to open public space

Rats are ubiquitous in urban environments and, as established reservoirs for infectious pathogens, present a control priority for public health agencies. New York City (NYC) harbors one of the largest rat populations in the United States, but surprising little study has been undertaken to define rat ecology across varied features of this urban landscape. More importantly, factors that may contribute to increased encounters between rats and humans have rarely been explored. Using city-wide records of rat sightings reported to the NYC Department of Health and Mental Hygiene, this investigation sought to identify sociodemographic, housing, and physical landscape characteristics that are associated with increased rat sightings across NYC census tracts. A hierarchical Bayesian conditional autoregressive Poisson model was used to assess these associations while accounting for spatial heterogeneity in the variance. Closer proximity to both subway lines and recreational public spaces was associated with a higher concentration of rat sightings, as was a greater presence of older housing, vacant housing units, and low education among the population. Moreover, these aspects of the physical and social landscape accurately predicted rat sightings across the city. These findings have identified specific features of the NYC urban environment that may help to provide direct control targets for reducing human–rat encounters.

Hepatitis E virus variant in farmed mink, Denmark

Hepatitis E virus (HEV) is a zoonotic virus for which pigs are the primary animal reservoir. To investigate whether HEV occurs in mink in Denmark, we screened feces and tissues from domestic and wild mink. Our finding of a novel HEV variant supports previous findings of HEV variants in a variety of species.

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.