高橋 雅春

Acute hepatitis E was considered rare until reports emerged affirming the existence of hepatitis E virus (HEV) genotypes 3 and 4 infections in Japan in the early 2000s. Extensive studies by Japanese researchers have highlighted the pivotal role of pigs and wild animals, such as wild boars and deer, as reservoirs for HEV, linking them to zoonotic infections in Japan. Currently, when hepatitis occurs subsequent to the consumption of undercooked or grilled pork, wild boar meat, or offal (including pig liver and intestines), HEV infection should be considered. Following the approval of anti-HEV immunoglobulin A antibody as a diagnostic tool for hepatitis E by Japan's Health Insurance System in 2011, the annual number of diagnosed cases of HEV infection has surged. Notably, the occurrence of post-transfusion hepatitis E promoted nationwide screening of blood products for HEV using nucleic acid amplification tests since 2020. Furthermore, chronic hepatitis E has been observed in immunosuppressed individuals. Considering the significance of hepatitis E, heightened preventive measures are essential. The Japan Agency for Medical Research and Development Hepatitis A and E viruses (HAV and HEV) Study Group, which includes special virologists and hepatologists, held a virtual meeting on February 17, 2024. Discussions encompassed pathogenesis, transmission routes, diagnosis, complications, severity factors, and ongoing and prospective vaccination or treatments for hepatitis E. Rigorous assessment of referenced studies culminated in the formulation of recommendations, which are detailed within this review. This comprehensive review presents recent advancements in HEV research and Japanese clinical practice guidelines for HEV infection.

Previously, we developed an infectious hepatitis E virus (HEV) harboring the nanoKAZ gene in the hypervariable region of the open reading frame 1 (ORF1) of the HEV3b (JE03-1760F/P10) genome and demonstrated the usefulness for screening anti-HEV drugs that inhibit the early infection process. In the present study, we constructed another reporter HEV (HEV3b-HiBiT) by placing a minimized HiBiT tag derived from NanoLuc luciferase at the 3 & PRIME;-end of the viral capsid (ORF2) coding sequence. It replicated efficiently in PLC/PRF/5 cells, produced membrane-associated particles identical to those of the parental virus, and was genetically stable and infectious. The HiBiT tag was fused to both secreted ORF2s (ORF2s-HiBiT) and ORF2c capsid protein (ORF2c-HiBiT). The ORF2c-HiBiT formed membrane-associated HEV particles (eHEV3b-HiBiT). By treating these particles with digitonin, we demonstrated that the HiBiT tag was expressed on the surface of capsid and was present inside the lipid membrane. To simplify the measurement of luciferase activity and provide a more convenient screening platform, we constructed an ORF2s-defective mutant (HEV3b-HiBiT/& UDelta;ORF2s) in which the secreted ORF2s are suppressed. We used this system to evaluate the effects of introducing small interfering RNAs and treatment with an inhibitor or accelerator of exosomal release on HEV egress and demonstrated that the effects on virus release can readily be analyzed. Therefore, HEV3b-HiBiT and HEV3b-HiBiT/& UDelta;ORF2s reporters may be useful for investigating the virus life cycle and can serve as a more convenient screening platform to search for candidate drugs targeting the late stage of HEV infection such as particle formation and release.

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 (HEV) is a major cause of acute viral hepatitis globally. Genotype 1 HEV (HEV-1) is responsible for multiple outbreaks in developing countries, causing high mortality rates in pregnant women. However, studies on HEV-1 have been hindered by its poor replication in cultured cells. The JE04-1601S strain recovered from a Japanese patient with fulminant hepatitis E who contracted HEV-1 while traveling to India was serially passaged 12 times in human cell lines. The cell-culture-generated viruses (passage 12; p12) grew efficiently in human cell lines, but the replication was not fully supported in porcine cells. A full-length cDNA clone was constructed using JE04-1601S_p12 as a template. It was able to produce an infectious virus, and viral protein expression was detectable in the transfected PLC/PRF/5 cells and culture supernatants. Consistently, HEV-1 growth was also not fully supported in the cell culture of cDNA-derived JE04-1601S_p12 progenies, potentially recapitulating the narrow tropism of HEV-1 observed in vivo. The availability of an efficient cell culture system for HEV-1 and its infectious cDNA clone will be useful for studying HEV species tropism and mechanisms underlying severe hepatitis in HEV-1-infected pregnant women as well as for discovering and developing safer treatment options for this condition.

A woman in her late 70 s was diagnosed with liver injury at a health examination. Despite treatment with ursodeoxycholic acid at a nearby hospital, her transaminase levels elevated in two peaks. She was transferred to our hospital 77 days after the health examination. She weighed 42 kg and had a low body mass index of 19.8 kg/m2. Viral markers, including immunoglobulin A (IgA) against hepatitis E virus (anti-HEV IgA), were negative. Drug-induced liver injury was negligible. We suspected autoimmune hepatitis because of the patient's female gender and positive antinuclear antibody. However, prednisolone and azathioprine failed to completely improve her hepatitis. On day 643, anti-HEV IgA was re-evaluated and found to be positive. She was diagnosed with autochthonous chronic hepatitis E because the virus strains in the preserved serum on day 77 and the serum on day 643 had identical nucleotide sequences (genotype 3a). Following prednisolone and azathioprine discontinuation, ribavirin (RBV) was administered for 3 months. HEV RNA disappeared and remained negative for more than 6 months after the cessation of RBV. The HEV RNA titer of 6.2 log10 copies/mL on day 77 was unusually high 2.5 months after the onset, suggesting that hepatitis E had already been chronic before immunosuppressive treatment for possible autoimmune hepatitis. After getting married at 23 years old, she had been a housewife and had no comorbidities that might deteriorate her immunity. Chronicity should be kept in mind when encountering HEV infection in elderly and underweight patients.