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

Animal reservoirs for hepatitis E virus within the Paslahepevirus genus

Hepatitis E virus (HEV) is responsible for acute hepatitis in humans. It is a single-stranded, positive-sense RNA virus that belongs to the Hepeviridae family. The majority of concerning HEV genotypes belong to the Paslahepevirus genus and are subsequently divided into eight genotypes. HEV genotypes 1 and 2 exclusively infect humans and primates while genotypes 3 and 4 infect both humans and other mammals. Whereas HEV genotypes 5 and 6 are isolated from wild boars and genotypes 7 and 8 were identified from camels in the United Arab Emirates and China, respectively. HEV mainly spreads from humans to humans via the fecal-oral route. However, some genotypes with the capability of zoonotic transmissions, such as 3 and 4 transmit from animals to humans through feces, direct contact, and ingestion of contaminated meat products. As we further continue to uncover novel HEV strains in various animal species, it is becoming clear that HEV has a broad host range. Therefore, understanding the potential animal reservoirs for this virus will allow for better risk management and risk mitigation of infection with HEV. In this review, we mainly focused on animal reservoirs for the members of the species Paslahepevirus balayani and provided a comprehensive list of the host animals identified to date.

Hepatitis E virus (HEV) open reading frame 2: Role in pathogenesis and diagnosis in HEV infections

Hepatitis E virus (HEV) infection occurs worldwide. The HEV genome includes three to four open reading frames (ORF1-4). ORF1 proteins are essential for viral replication, while the ORF3 protein is an ion channel involved in the exit of HEV from the infected cells. ORF2 proteins form the viral capsid required for HEV invasion and assembly. They also suppress interferon production and inhibit antibody-mediated neutralisation of HEV, allowing the virus to hijack the host immune response. ORF2 is the only detectable viral protein in the human liver during HEV infection and it is secreted in the plasma, stool, and urine of HEV-infected patients, making it a reliable diagnostic marker. The plasma HEV ORF2 antigen level can predict the outcome of HEV infections. Hence, monitoring HEV ORF2 antigen levels may be useful in assessing the efficacy of anti-HEV therapy. The ORF2 antigen is immunogenic and includes epitopes that can induce neutralising antibodies; therefore, it is a potential HEV vaccine candidate. In this review, we highlighted the different forms of HEV ORF2 protein and their roles in HEV pathogenesis, diagnosis, monitoring the therapeutic efficacy, and vaccine development.

Hepatitis Viruses Control Host Immune Responses by Modifying the Exosomal Biogenesis Pathway and Cargo

The development of smart immune evasion mechanisms is crucial for the establishment of acute and chronic viral hepatitis. Hepatitis is a major health problem worldwide arising from different causes, such as pathogens, metabolic disorders, and xenotoxins, with the five hepatitis viruses A, B, C, D, and E (HAV, HBV, HCV, HDV, and HEV) representing the majority of the cases. Most of the hepatitis viruses are considered enveloped. Recently, it was reported that the non-enveloped HAV and HEV are, in reality, quasi-enveloped viruses exploiting exosomal-like biogenesis mechanisms for budding. Regardless, all hepatitis viruses use exosomes to egress, regulate, and eventually escape from the host immune system, revealing another key function of exosomes apart from their recognised role in intercellular communication. This review will discuss how the hepatitis viruses exploit exosome biogenesis and transport capacity to establish successful infection and spread. Then, we will outline the contribution of exosomes in viral persistence and liver disease progression.

The Unmet Needs of Hepatitis E Virus Diagnosis in Suspected Drug-Induced Liver Injury in Limited Resource Setting

Background: Currently, there are no specific biomarkers for drug-induced liver injury (DILI), and the diagnosis of DILI is based mainly on the exclusion of other causes of liver dysfunction and the recognition of potential causative drugs. Hepatitis E virus (HEV) diagnosis is not routinely enrolled in many countries, and HEV infection could be misdiagnosed as DILI.

Methodology: We retrospectively analyzed plasma samples (n = 80) collected from suspected DILI for HEV markers such as anti-HEV IgM, anti-HEV IgG, and HEV RNA. Anti-HEV antibodies were assessed using commercial ELISA kits. HEV RNA was tested by RT-qPCR targeting HEV ORF2/3, the receiver operating characteristic (ROC) curve was plotted, and a putative threshold for liver function parameters was determined.

Results: Out of 80 samples, 12 samples were positive for anti-HEV IgM and anti-HEV IgG, and HEV RNA was detected in seven samples. The median viral load was 3.46 × 10³ IU/ml, and the isolated viruses belonged to HEV genotype 1. The level of liver enzymes such as alanine transaminase (ALT) and aspartate transaminase (AST), but not alkaline phosphatase (ALP), was significantly higher in HEV confirmed cases than in non-HEV confirmed cases. We identified a plasma ALT level of at least 415.5 U/L and AST level of at least 332 U/L; ALT/ALP ratio of at least 5.08 could be used as a guide for the patients diagnosed as DILI to be tested for HEV infection. The previous liver function parameters showed high sensitivity and good specificity.

Conclusion: Hepatitis E virus was detected in suspected DILI cases. The diagnosis of DILI is not secure until HEV testing is done. Liver function parameters can be used as a guide for HEV testing in suspected DILI cases in countries with limited resources.

Hepatitis E Virus Persistence and/or Replication in the Peripheral Blood Mononuclear Cells of Acute HEV-Infected Patients

BACKGROUND

Hepatitis E virus (HEV) causes about 14 million infections with 300,000 deaths and 5,200 stillbirths worldwide annually. Extrahepatic manifestations are reported with HEV infections, such as renal, neurological, and hematological disorders. Recently, we reported that stool-derived HEV-1 replicates efficiently in human monocytes and macrophages in vitro. However, another study reports the presence of viral RNA but no evidence of replication in the PBMCs of acute hepatitis E (AHE) patients. Therefore, the replication of HEV in PBMCs during AHE infection is not completely understood.

METHODS

PBMCs were isolated from AHE patients (n = 17) enrolled in Assiut University Hospitals, Egypt. The viral load, positive (+) and negative (-) HEV RNA strands and viral protein were assessed. The gene expression profile of PBMCs from AHE patients was assessed. In addition, the level of cytokines was measured in the plasma of the patients.

RESULTS

HEV RNA was detected in the PBMCs of AHE patients. The median HEV load in the PBMCs was 1.34 × 103 IU/ml. A negative HEV RNA strand and HEV open reading frame 2 protein were recorded in 4/17 (23.5%) of the PBMCs. Upregulation of inflammatory transcripts and increased plasma cytokines were recorded in the AHE patients compared with healthy individuals with significantly elevated transcripts and plasma cytokines in the AHE with detectable (+) and (-) RNA strands compared with the AHE with the detectable (+) RNA strand only. There was no significant difference in terms of age, sex, and liver function tests between AHE patients with detectable (+) and (-) RNA strands in the PBMCs and AHE patients with the (+) RNA strand only.

CONCLUSION

Our study shows evidence for in vivo HEV persistence and replication in the PBMCs of AHE patients. The replication of HEV in the PBMCs was associated with an enhanced immune response, which could affect the pathogenesis of HEV.

Hepatitis E and Pregnancy: An Unholy Alliance Unmasked from Kashmir, India

The adverse relationship between viral hepatitis and pregnancy in developing countries had been interpreted as a reflection of retrospectively biased hospital-based data collection by the West. However, the discovery of hepatitis E virus (HEV) as the etiological agent of an epidemic of non-A, non-B hepatitis in Kashmir, and the documenting of the increased incidence and severity of hepatitis E in pregnancy via a house-to-house survey, unmasked this unholy alliance. In the Hepeviridae family, HEV-genotype (gt)1 from genus Orthohepevirus A has a unique open reading frame (ORF)4-encoded protein which enhances viral polymerase activity and viral replication. The epidemics caused by HEV-gt1, but not any other Orthohepevirus A genotype, show an adverse relationship with pregnancy in humans. The pathogenesis of the association is complex and at present not well understood. Possibly multiple factors play a role in causing severe liver disease in the pregnant women including infection and damage to the maternal-fetal interface by HEV-gt1; vertical transmission of HEV to fetus causing severe fetal/neonatal hepatitis; and combined viral and hormone related immune dysfunction of diverse nature in the pregnant women, promoting viral replication. Management is multidisciplinary and needs a close watch for the development and management of acute liver failure. (ALF). Preliminary data suggest beneficial maternal outcomes by early termination of pregnancy in patients with lower grades of encephalopathy.

Experimental Methods to Study the Pathogenesis of Human Enteric RNA Viruses

Every year, millions of children are infected with viruses that target the gastrointestinal tract, causing acute gastroenteritis and diarrheal illness. Indeed, approximately 700 million episodes of diarrhea occur in children under five annually, with RNA viruses norovirus, rotavirus, and astrovirus serving as major causative pathogens. Numerous methodological advancements in recent years, including the establishment of novel cultivation systems using enteroids as well as the development of murine and other animal models of infection, have helped provide insight into many features of viral pathogenesis. However, many aspects of enteric viral infections remain elusive, demanding further study. Here, we describe the different in vitro and in vivo tools available to explore different pathophysiological attributes of human enteric RNA viruses, highlighting their advantages and limitations depending upon the question being explored. In addition, we discuss key areas and opportunities that would benefit from further methodological progress.

Evaluation of hepatitis E antigen kinetics and its diagnostic utility for prediction of the outcomes of hepatitis E virus genotype 1 infection

HEV-Ag ELISA assay is a reliable diagnostic test in resource-limited areas. HEV genotype 1 (HEV-1) infections are either self-limited or progress to fulminant hepatic failure (FHF) and death if anti-HEV therapy is delayed. Limited data is available about the diagnostic utility of HEV Ag on HEV-1 infections. Herein wWe aimed to study the kinetics of HEV Ag during HEV-1 infections at different stages, i.e., acute HEV infection, recovery, and progression to FHF. Also, we evaluated the diagnostic utility of this marker to predict the outcomes of HEV-1 infections. Plasma of acute hepatitis E (AHE) patients were assessed for HEV RNA by RT-qPCR, HEV Ag, and anti-HEV IgM by ELISA. The kinetics of HEV Ag was monitored at different time points; acute phase of infection, recovery, FHF stage, and post-recovery. Our results showed that the level of HEV Ag was elevated in AHE patients with a significantly higher level in FHF patients than recovered patients. We identified a plasma HEV Ag threshold that can differentiate between self-limiting infection and FHF progression with 100% sensitivity and 88.89% specificity. HEV Ag and HEV RNA have similar kinetics during the acute phase and self-limiting infection. In the FHF stage, HEV Ag and anti-HEV IgM have similar patterns of kinetics which could be the cause of liver damage. In conclusion, the HEV Ag assay can be used as a biomarker for predicting the consequences of HEV-1 infections which could be diagnostically useful for taking the appropriate measures to reduce the complications, especially for high-risk groups.