Hepatitis E

Search ⌘K Suggest Edit Sign in Signs and symptoms Virology Pathogenesis Diagnosis Prevention Treatment Epidemiology History and evolution References Fact-checked by Grok 7 months ago Hepatitis E Hepatitis E is an acute viral infection of the liver caused by the hepatitis E virus (HEV), a small, non-enveloped, single-stranded RNA virus belonging to the family Hepeviridae.[1][2] The virus primarily spreads through the fecal-oral route, often via ingestion of contaminated water in areas with poor sanitation, though zoonotic transmission from animals like pigs occurs with certain genotypes in developed regions.[1][3] There are four main genotypes infecting humans: genotypes 1 and 2 are human-exclusive and cause large waterborne outbreaks in developing countries, while genotypes 3 and 4 are zoonotic and more common in industrialized nations.[1][2] Globally, hepatitis E is a leading cause of acute viral hepatitis, with an estimated 19.47 million incident cases and 3,450 deaths in 2021, predominantly in Southeast Asia and sub-Saharan Africa.[1] In endemic areas, infections often occur in young adults aged 15–40 through sporadic cases or epidemics, while in low-endemic regions like the United States and Europe, it is rare but increasingly recognized in travelers or via undercooked meat consumption.[1][3] The incubation period typically lasts 2–6 weeks, after which most infections are self-limiting, resolving within 1–6 weeks without long-term liver damage in immunocompetent individuals.[3][2] Clinical symptoms, when present, include fever, fatigue, nausea, abdominal pain, and jaundice, affecting 5–30% of cases; however, the infection can be asymptomatic or severe, particularly in high-risk groups.[1] Pregnant women, especially in the third trimester, face a mortality rate of up to 20–25% due to fulminant hepatic failure with genotypes 1 and 2, while immunocompromised patients (e.g., organ transplant recipients) may develop chronic hepatitis with genotypes 3 and 4.[1][2] Extrahepatic manifestations, such as neurological disorders like Guillain-Barré syndrome, have also been associated with HEV infection.[2] Diagnosis involves detecting anti-HEV IgM antibodies for acute infection or HEV RNA via nucleic acid amplification tests in blood or stool, with IgG indicating past exposure.[3][2] There is no specific antiviral treatment for acute cases, which are managed supportively; ribavirin is used for chronic infections in immunocompromised patients, though it is contraindicated in pregnancy.[1][2] Prevention focuses on ensuring access to safe drinking water, proper sanitation, and hygiene practices to interrupt fecal-oral transmission.[1] A recombinant vaccine (HEV 239, marketed as Hecolin) is licensed in China and Pakistan, with WHO recommending its use in specific high-risk outbreak settings, and has shown over 95% efficacy in healthy adults, with recent use in outbreak responses like those in South Sudan in 2022–2023, including campaigns in 2023 in Fangak County, following WHO's 2024 recommendations for targeted vaccination in outbreak settings.[1][4] In developed countries, avoiding raw or undercooked pork and wild game helps mitigate zoonotic risks.[3] Signs and symptoms Acute infection Acute hepatitis E infection typically follows an incubation period of 2 to 8 weeks after exposure to the hepatitis E virus (HEV). The illness progresses through distinct phases, beginning with a prodromal (pre-icteric) phase characterized by nonspecific symptoms such as mild fever, anorexia, nausea, vomiting, and abdominal pain, which usually last 2 to 10 days.[1][5] These early symptoms reflect the initial viral replication and immune response in the liver and gastrointestinal tract, often resolving as the infection advances.[6] The prodromal phase transitions into the icteric phase, marked by the onset of jaundice, dark urine, pale stools, and pruritus due to cholestasis. Physical examination may reveal hepatomegaly in 10% to 85% of cases, along with right upper quadrant tenderness. Laboratory findings during this phase include markedly elevated serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, often peaking at 10 to 20 times the upper limit of normal, alongside increased bilirubin concentrations.[1][5][7] These hepatic enzyme elevations indicate hepatocellular injury and are typically accompanied by positive IgM anti-HEV antibodies, which serve as a key serological marker for acute infection.[1][8] The overall duration of acute hepatitis E is generally 1 to 6 weeks, with the icteric phase lasting several days to weeks before symptoms subside. In immunocompetent individuals, full clinical and biochemical recovery occurs in 95% to 99% of cases, and the infection is self-limiting without progression to chronicity.[1][6] However, a substantial proportion of HEV infections—often the majority—are asymptomatic and only identified through serological testing or incidental detection during screening.[1][9] Chronic infection Chronic hepatitis E is defined as persistent hepatitis E virus (HEV) viremia lasting more than 3 months, primarily affecting immunocompromised individuals.[10] In such populations, including solid organ transplant recipients and those with hematologic malignancies, the risk of developing chronic infection ranges from 10% to 60%, with higher rates observed in solid organ transplant patients exposed to genotype 3 HEV.[11] This contrasts with immunocompetent hosts, where acute infections typically resolve spontaneously within 4-6 weeks. As of 2025, improved diagnostics have contributed to rising reported chronic HEV cases in China, emphasizing its status as a neglected cause of liver disease in immunocompromised groups.[12] Symptoms of chronic hepatitis E are frequently absent or mild, with fatigue being the most common manifestation reported in up to 24% of cases, alongside occasional diarrhea or arthralgia.[13] Key risk factors include organ transplantation, chemotherapy, high-dose immunosuppressive therapy such as tacrolimus, and underlying conditions like HIV infection.[14] In developed countries, genotype 3 HEV predominates in these chronic cases, often linked to zoonotic transmission from swine reservoirs.[12] Untreated chronic hepatitis E can lead to progressive liver fibrosis and cirrhosis in approximately 10% of affected individuals within 2 years, potentially advancing to end-stage liver disease.[11] Extrahepatic complications, such as immune complex-mediated glomerulonephritis, have also been documented, particularly in kidney transplant recipients with persistent viremia.[15] As of 2025, chronic hepatitis E is increasingly recognized as a "neglected liver killer," with rising incidence noted in China, where the average annual increase in hepatitis E cases has been around 7% from 2002 to 2021, driven partly by genotype 4 strains in immunocompromised groups.[16][12] Extrhepatic manifestations Hepatitis E virus (HEV) infection can lead to various extrhepatic manifestations, affecting systems beyond the liver, with neurological involvement being among the most frequently reported. These manifestations are often linked to immune-mediated processes and are more common in genotype 3 infections prevalent in developed regions.[17][18] Neurological complications occur in approximately 5-30% of acute HEV cases, depending on study populations, with Guillain-Barré syndrome (GBS) and neuralgic amyotrophy (also known as Parsonage-Turner syndrome) being the predominant presentations. GBS, characterized by acute ascending paralysis and areflexia, has been documented in multiple cases associated with acute HEV, particularly genotype 3, where anti-HEV IgM positivity confirms the temporal link. Neuralgic amyotrophy presents with severe shoulder pain followed by muscle weakness and atrophy, reported in up to 10% of symptomatic HEV infections in some cohorts. Encephalitis, involving brain inflammation with altered mental status and seizures, is rarer but has been observed in immunocompromised patients with chronic HEV. These neurological events are predominantly peripheral but can extend to central involvement, with most cases resolving with supportive care and ribavirin in chronic settings.[19][20][21] Renal manifestations are less common but significant, especially in chronic HEV infections among immunocompromised individuals, where membranoproliferative glomerulonephritis (MPGN) and cryoglobulinemia predominate. MPGN features mesangial proliferation and immune deposits leading to proteinuria and hematuria, often confirmed by renal biopsy showing subendothelial deposits. Cryoglobulinemia has been reported in approximately 50-70% of chronic HEV cases in solid-organ transplant recipients, with higher rates (up to 67%) in kidney transplant patients; recent 2024 studies highlighting HEV ORF2 protein-antibody complexes in glomerular deposits as a key pathogenic feature.[22][15][23] These renal effects are more prevalent in genotype 3 and 4 infections, contributing to progressive kidney dysfunction if untreated. Hematological abnormalities, though rare, include thrombocytopenia and hemolytic anemia, observed in acute outbreaks and chronic cases. Thrombocytopenia, with platelet counts below 100,000/μL, affects up to 20% of acute HEV patients and may result from bone marrow suppression or immune destruction. Hemolytic anemia, including autoimmune forms, is infrequent but documented in outbreaks, particularly in glucose-6-phosphate dehydrogenase-deficient individuals, leading to jaundice and fatigue beyond hepatic involvement. These events typically resolve with HEV clearance but can exacerbate severity in vulnerable populations.[24][25] Other extrhepatic effects encompass pancreatitis and myocarditis, alongside post-infection autoimmune associations. Acute pancreatitis, marked by elevated amylase and lipase, has been reported in symptomatic HEV cases, often self-limiting but potentially severe. Myocarditis, presenting with chest pain and arrhythmias, is exceptional but reported in acute infections, with histopathological evidence of myocardial inflammation. Post-infection autoimmune phenomena, such as thyroiditis or arthritis, have been noted in follow-up studies, suggesting persistent immune dysregulation.[26][27] The underlying mechanisms for these extrhepatic manifestations primarily involve immune-mediated pathways, including molecular mimicry—where HEV epitopes cross-react with host proteins, as proposed for neurological disorders—and immune complex deposition, evident in renal cryoglobulinemia and glomerulonephritis. Direct viral replication in extrahepatic tissues may contribute in chronic cases, but indirect immune responses predominate, with recent evidence from 2024 confirming antigen-antibody complexes in affected organs. Cryoglobulinemia prevalence in chronic HEV remains around 10% in high-risk groups, with no major shifts reported in early 2025 data.[28][29][15] Complications in pregnancy Hepatitis E virus (HEV) infection poses a significantly heightened risk during pregnancy, particularly in the third trimester, where it can lead to fulminant hepatic failure and maternal mortality rates of 20-30%.[30] This severe outcome is more common with HEV genotypes 1 and 2, prevalent in endemic regions of Asia and Africa, compared to genotypes 3 and 4 found in developed countries.[31] The infection often progresses rapidly from acute hepatitis symptoms such as jaundice and abdominal pain to life-threatening complications including coagulopathy and hepatic encephalopathy, with the interval from jaundice to encephalopathy as short as 1-3 days in many cases.[32] Risk factors for severe disease include infection in the third trimester, where mortality can reach 21-32%, as well as hormonal and immunological changes during pregnancy that impair viral clearance and exacerbate liver injury.[33] Inadequate antenatal care and poor sanitation in endemic areas further amplify vulnerability.[34] Obstetric complications such as premature rupture of membranes and preterm delivery occur in over 70% of affected pregnancies, contributing to poor maternal-fetal outcomes.[34] Fetal effects are profound, with stillbirth and miscarriage rates ranging from 20-50%, and intrauterine fetal demise reported in up to 77% of cases in some cohorts.[34] Vertical transmission occurs in 30-50% of cases, often leading to preterm birth, low birth weight, and neonatal hepatic issues, though the virus's impact on the fetus is mediated more through placental dysfunction than direct infection in many instances.[35] Recent studies from 2024 have assessed the HEV239 vaccine's safety in pregnancy; while no increased risk of fetal loss was observed overall and benefits outweigh risks in high-risk settings, a higher rate of spontaneous abortion was noted if administered within 90 days before or during early pregnancy, supporting strategies to avoid exposure in early pregnancy.[36] Virology Classification and genotypes Hepatitis E virus (HEV) is classified within the family Hepeviridae, specifically in the genus Orthohepevirus A, as a single-stranded, positive-sense RNA virus with a non-enveloped or quasi-enveloped structure and a genome approximately 7.2 kilobases in length.[37][6] This taxonomic placement reflects its enterically transmitted nature and close relation to other mammalian-infecting hepeviruses, distinguishing it from genera like Piscihepevirus (fish viruses) or Rocahepevirus (rat viruses).[38] HEV is further divided into eight recognized genotypes (1 through 8), based on phylogenetic analysis showing nucleotide sequence divergences typically exceeding 20-25% between genotypes.[39] Genotypes 1 and 2 are exclusively human pathogens, primarily spread through contaminated water in endemic regions with poor sanitation.[1] In contrast, genotypes 3 and 4 are zoonotic, with pigs serving as the main reservoir, facilitating transmission to humans via undercooked meat or direct contact.[1] Genotype 7 is associated with camels as the primary host and has been linked to human infections, while genotypes 5 and 6 have been identified exclusively in wild boars, particularly in Japan, with no confirmed human infections to date; genotype 8 has been detected in Bactrian camels in China, also without confirmed human cases as of 2025.[40][41] Within genotypes, subtypes are defined by lower divergence thresholds (around 15-20%), with genotype 3 exhibiting the greatest diversity, encompassing at least 14 recognized subtypes (3a through 3m and 3ra) and numerous unclassified variants.[42] These subtypes can influence pathogenicity and geographic prevalence; for instance, subtype 3f predominates in Europe and has been linked to foodborne outbreaks, potentially due to variations in host adaptation and immune evasion.[43] As of 2025, ongoing reclassification proposals under the International Committee on Taxonomy of Viruses (ICTV) emphasize genetic divergence metrics greater than 20% for genotype boundaries, incorporating emerging sequences from animal reservoirs to refine zoonotic risk assessments.[39] Geographic distribution Hepatitis E virus (HEV) genotypes 1 and 2 are predominantly associated with endemic transmission in developing regions of Asia and Africa, where they cause both epidemic outbreaks and sporadic cases through fecal-oral routes. In South Asia, particularly India, and sub-Saharan Africa, these genotypes lead to hyperendemic patterns with seroprevalence often exceeding 3% in general populations, and higher rates in high-risk groups such as rural communities with poor sanitation. For instance, studies in Nepal, Bangladesh, and parts of West Africa report anti-HEV IgG seroprevalence ranging from 15% to over 50% in adults, reflecting ongoing environmental contamination and waterborne spread in these areas.[44][45][46] In contrast, genotypes 3 and 4 are linked to sporadic and zoonotic infections in industrialized regions like Europe and North America, where human cases are typically autochthonous and associated with consumption of undercooked pork or game meat. Seroprevalence for these genotypes in these areas generally falls between 1% and 20%, with higher rates observed in older adults and rural populations exposed to animal reservoirs; for example, in the United States and Canada, anti-HEV antibodies are detected in 5-18% of blood donors as of 2024, while in Europe, rates vary from 0.6% in southern countries to over 20% in parts of France and Germany.[47][48][46][49] Genotype 3 predominates in Europe and North America, often transmitted via swine products, whereas genotype 4 is more common in East Asia but has been increasingly reported in European cases.[47][48][46] Emerging patterns include the detection of genotype 7, primarily in the Middle East, where it circulates in dromedary camels and has been linked to human infections through consumption of camel meat or milk. Cases of genotype 7 have been reported in the United Arab Emirates, Israel, and Saudi Arabia, marking it as a potential new zoonotic threat in arid regions with camel husbandry. Additionally, autochthonous infections by genotypes 3 and 4 are rising in developed countries, driven by local animal reservoirs and foodborne transmission from wild game such as boar.[50][51][52] As of 2025, HEV infections show increasing trends in specific regions, with genotype 4 cases rising in China due to expanding swine reservoirs and changing dietary habits, contributing to over 28,000 reported annual cases nationwide. In Europe, genotype 3 infections linked to game meat consumption, particularly wild boar, have surged, with notifications doubling in some countries since 2020. The World Health Organization estimates approximately 20 million new HEV infections globally each year, underscoring the virus's persistent burden across diverse geographic settings.[53][54][1] Transmission routes Hepatitis E virus (HEV) is primarily transmitted through the fecal-oral route, particularly in endemic areas where contaminated drinking water serves as the main vehicle for spread. This mode of transmission is most common with genotypes 1 and 2, which are predominantly human pathogens and cause large waterborne outbreaks in regions with poor sanitation, such as parts of Asia, Africa, and Latin America. Contaminated food, including raw or undercooked shellfish, vegetables irrigated with sewage-contaminated water, or fruits, can also facilitate infection via this route. The infectivity of HEV is dose-dependent, with the lowest observed infectious dose estimated at approximately 7 × 10^3 international units (IU), though higher doses of 10^4 to 10^6 particles are typically required for reliable transmission in experimental models.[1][55][56] In non-endemic regions, particularly in developed countries, zoonotic transmission predominates for genotypes 3 and 4, which are shared between humans and animals. Consumption of undercooked pork, wild boar, or deer meat is a key risk factor, as the virus can persist in these animal tissues even after slaughter. Occupational exposure among farmers, veterinarians, and slaughterhouse workers increases susceptibility through direct contact with infected animal feces or blood, highlighting the role of swine as a major reservoir in these transmission events.[55][56][6] Other transmission routes are less common but documented. Blood transfusion poses a risk in endemic areas, where viremic donors can transmit HEV; in high-prevalence settings like parts of Asia, HEV RNA prevalence in blood donors is approximately 0.1-0.14% as of 2023. Vertical transmission from mother to fetus occurs rarely, primarily with genotype 1 during pregnancy, contributing to high fetal mortality but not routine spread. Unlike hepatitis A, routine person-to-person or sexual transmission is not observed, though sporadic household contacts have been noted in outbreak settings.[57][58] The incubation period for HEV infection typically ranges from 2 to 10 weeks, with a mean of 5 to 6 weeks, during which the virus replicates in the liver without symptoms. The infectious period follows, lasting about 1 to 2 weeks after symptom onset, when fecal shedding peaks and declines rapidly, limiting secondary spread. European surveillance data indicate ongoing foodborne HEV cases, particularly genotype 3 infections.[1][6] Animal reservoirs Hepatitis E virus (HEV) maintains its zoonotic potential through various animal reservoirs, with domestic pigs and wild boars serving as primary hosts for genotype 3 strains prevalent in Europe, North America, and Asia.[59] These animals facilitate viral persistence and spillover to humans, with seroprevalence rates in domestic pigs reaching approximately 60% globally and 27% in wild boars, though individual herd infection rates can vary widely from 1% to 89% depending on region and management practices.[59][60] In swine herds, HEV infection often occurs asymptomatically in pigs aged 2-4 months, with vertical transmission documented from infected sows to piglets, contributing to sustained circulation within farms.[61][62] Camels act as key reservoirs for genotype 7 HEV, particularly dromedary camels in the Middle East and Bactrian camels in China, where the virus has been detected in fecal samples and linked to human infections via consumption of camel products.[63][64] Rabbits harbor genotype 3ra variants, a subtype of genotype 3, with evidence of natural infection in feral and domestic rabbits across Europe and Asia, raising concerns for zoonotic transmission due to genetic similarity with human strains.[65][66] Zoonotic spillover from these reservoirs involves cross-species adaptation facilitated by the viral capsid protein encoded by open reading frame 2 (ORF2) and the multifunctional phosphoprotein from ORF3, which aid in virion morphogenesis and host cell interactions.[67] Experimental studies have demonstrated HEV infectivity in non-primary hosts, including chickens and rats, highlighting the virus's broad host range potential beyond established reservoirs.[68][69] Genotype 3 subtypes exhibit varying degrees of host adaptation, with some strains showing enhanced replication in pigs or wild boars, influencing their zoonotic efficiency.[70] Public health risks are elevated in settings involving close animal contact, such as pig farming and wild boar hunting, where occupational exposure through contaminated environments or undercooked meat has led to documented human cases.[71][72] Recent 2025 analyses of chirohepeviruses in bats reveal genetic relatedness to Orthohepevirus A (including HEV) but position them as distant relatives rather than direct reservoirs for human-pathogenic strains.[73] Genome structure The Hepatitis E virus (HEV) genome is a single-stranded, positive-sense RNA molecule approximately 7.2 kilobases (kb) in length, featuring a 5' cap structure and a 3' polyadenylated tail that mimic eukaryotic mRNA to facilitate translation and stability. This non-enveloped virus belongs to the family Hepeviridae, and its genome organization is conserved across genotypes, enabling efficient replication in host cells.[74][75] The genome contains three partially overlapping open reading frames (ORFs). ORF1, the largest at about 5,082 nucleotides, encodes a 1,699-amino-acid nonstructural polyprotein that serves as the replicase complex, incorporating domains such as methyltransferase (for 5' capping), a Y domain (of unknown function), papain-like cysteine protease, X domain (macrodomain for ADP-ribose binding), helicase, and RNA-dependent RNA polymerase (for genome replication). ORF2 spans 1,983 nucleotides and produces a 660-amino-acid capsid protein essential for virion assembly and host cell attachment. ORF3, overlapping with ORF2, encodes a 123-amino-acid multifunctional phosphoprotein that regulates viral egress and interacts with host cytoskeleton components.[74][76][77] A key feature within ORF1 is the hypervariable region (HVR), a proline-rich domain (approximately amino acids 711-798 in genotype 1) that exhibits pronounced sequence and length variability through insertions and deletions, enabling immune evasion and adaptation to host pressures without compromising overall replication. This region's heterogeneity, including host-derived insertions like those from the human RPS17 gene in the Kernow-C1 strain, enhances viral fitness and persistence.[74][78][79] HEV genotypes display 20-40% nucleotide divergence, with zoonotic genotypes 3 and 4 showing greater intra-genotypic variability (up to 25%) compared to human-specific genotypes 1 and 2, reflecting evolutionary pressures from diverse reservoirs. Recombination is rare but documented, often occurring in the HVR and contributing to emergent strains with altered pathogenicity. Recent analyses of genotype 3 genomes indicate constrained evolution in core functional domains (e.g., low entropy in methyltransferase and Y domain), where variability is compartmentalized to the HVR to balance stability and adaptability.[80][81][76] Updates from 2024-2025 research identify specific genetic determinants in HVR insertions—such as nuclear localization signals and post-translational modification sites—that drive chronicity in immunocompromised patients by boosting replication efficiency, as seen in zoonotic strains with human gene integrations. These findings, coupled with HVR's high mutation rates aligning closely with full-genome phylogenies, underscore its value for tracking viral evolution and epidemiology.[78][79] Replication cycle Hepatitis E virus (HEV) initiates its replication cycle by entering host hepatocytes through receptor-mediated endocytosis. The asialoglycoprotein receptor (ASGPR) facilitates attachment and entry by interacting with the viral capsid protein encoded by open reading frame 2 (ORF2), as demonstrated in studies using hepatocyte cell lines.[82] Heparan sulfate proteoglycans (HSPGs) also serve as attachment factors for non-enveloped HEV particles, promoting initial binding to the cell surface.[83] Both non-enveloped and quasi-enveloped forms of HEV are internalized via clathrin- and dynamin 2-dependent pathways, with quasi-enveloped particles (eHEV) additionally requiring endosomal trafficking through Rab5- and Rab7-positive compartments and lysosomal lipid degradation mediated by Niemann-Pick C1 protein.[84] Following endocytosis, the viral capsid uncoats in the endolysosomal compartment, releasing the positive-sense, single-stranded RNA genome into the cytoplasm.[85] Replication occurs exclusively in the cytoplasm, often associated with modified endoplasmic reticulum membranes forming replication complexes. The RNA-dependent RNA polymerase (RdRp) within the non-structural polyprotein encoded by ORF1 first synthesizes a complementary negative-sense RNA strand using the genomic RNA as a template. This negative strand then directs the production of new positive-sense genomic RNAs for packaging and subgenomic RNAs (sgRNAs) via a subgenomic promoter located in the junction region between ORF1 and ORF2/ORF3. The sgRNAs are translated into the ORF2 capsid protein and ORF3 protein, which functions as a viroporin to modulate host membranes.[86][87] Host factors such as the eukaryotic initiation factor 4F (eIF4F) complex support translation of the genomic RNA, while microRNA-122 enhances replication efficiency.[88] The hypervariable region (HVR) within ORF1 contributes to replication by tolerating insertions and deletions that aid in adapting to host restrictions and evading innate immune detection through sequence variability. HEV exhibits a characteristically slow replication rate in cell culture models, producing on the order of 10^3 to 10^4 genomic copies per infected cell per day, which limits peak titers compared to more robustly replicating viruses. Viral assembly begins with the non-glycosylated form of the ORF2 capsid protein self-assembling into empty icosahedral T=1 capsids in the cytoplasm, which subsequently package the positive-sense genomic RNA to form mature non-enveloped virions.[89] The ORF3 protein recruits these capsids to intracellular membranes, enabling two distinct particle types: non-enveloped virions released into bile and quasi-enveloped particles (eHEV) in circulating blood, where the envelope is acquired from host endosomal lipids without incorporating viral glycoproteins. This quasi-envelopment shields the capsid from neutralizing antibodies, enhancing systemic persistence. Mature virions are released primarily through exocytosis. Quasi-enveloped HEV egresses via multivesicular body (MVB) fusion with the plasma membrane, dependent on the endosomal sorting complex required for transport (ESCRT) components such as Tsg101, Hrs, and Vps4, as well as Rab27a-mediated trafficking.[90] Non-enveloped particles are secreted apically into bile canaliculi. HEV can persist intracellularly within lysosomal compartments, potentially contributing to chronic infection in susceptible hosts.[84] Pathogenesis Initial infection and immune response Hepatitis E virus (HEV) primarily enters the host through the fecal-oral route, with the virus crossing the intestinal mucosa and reaching the liver via the portal vein. Recent studies indicate that entry into hepatocytes involves integrin beta 1 (ITGB1) facilitating interaction with the ORF2 protein.[91][92] Once in hepatocytes, HEV replicates efficiently, leading to low-level viremia that typically peaks shortly before symptom onset and persists for about 1-2 weeks.[93] In contrast, fecal shedding is robust and prolonged, often beginning 1-2 weeks before viremia and continuing for 2-4 weeks after, facilitating high transmissibility during the early infection phase.[94] The innate immune response to HEV is notably subdued, characterized by a weak type I interferon (IFN) production that fails to mount a robust antiviral defense.[95] HEV achieves this evasion primarily through its ORF1-encoded products, which inhibit the phosphorylation and activation of interferon regulatory factor 3 (IRF3), thereby suppressing downstream IFN-β induction.[96] This interference with IRF3 signaling, along with potential modulation of IRF1 pathways, allows the virus to replicate with minimal early innate restriction in hepatocytes.[97] Adaptive immunity plays a critical role in controlling acute HEV infection, with humoral and cellular components emerging sequentially. Anti-HEV IgM antibodies targeting the capsid protein (ORF2) and phosphoprotein (ORF3) appear within 1-4 weeks post-infection, marking the acute phase.[98] These are followed by neutralizing IgG antibodies against ORF2, which correlate with viral clearance. Analyses as of 2025 reveal evolutionary drivers in HEV, such as immune escape considerations in neutralization epitopes of ORF2, where glycosylated decoys may partially evade antibody recognition, though potent glycan-sensitive broadly neutralizing antibodies (bnAbs) confer protection.[99][100][101] Concurrently, CD8+ T cells specific to ORF2 epitopes expand and target infected hepatocytes, contributing substantially to the resolution of viremia and fecal shedding.[102] In over 95% of immunocompetent individuals, HEV infection resolves asymptomatically within 4-8 weeks, driven by the development of protective neutralizing antibodies that persist long-term.[103] This efficient clearance underscores the effectiveness of the adaptive response in most cases, with viremia and shedding ceasing as antibody titers peak.[104] Progression to chronic disease Hepatitis E virus (HEV) infection typically resolves spontaneously in immunocompetent individuals, but progression to chronic disease occurs primarily through impaired viral clearance mechanisms. Persistence is facilitated by an inadequate T-cell response, particularly in immunosuppressed hosts, where HEV-specific CD8+ T cells fail to mount an effective cytotoxic attack, allowing ongoing viral replication and high viremia levels. Additionally, insertions in the hypervariable region (HVR) of the HEV genome, such as host-derived RNA sequences from genes like TRIM22 or SERPINA1, enable immune evasion by altering viral antigenicity and enhancing replication efficiency, thereby sustaining high viral loads that overwhelm initial immune control.[105][106] Host factors play a critical role in this progression, with immunosuppression being the dominant risk. In solid organ transplant recipients, regimens involving tacrolimus are associated with higher rates of chronicity compared to cyclosporine, as tacrolimus more potently inhibits T-cell activation and proliferation, leading to prolonged viremia (e.g., tacrolimus trough levels >9 ng/mL correlate with chronic infection in up to 60% of cases). Similarly, in HIV-infected individuals, CD4 counts below 200 cells/mm³ significantly elevate the risk, with seroprevalence reaching 16% in this subgroup versus 4.5% in those with higher counts, due to diminished adaptive immunity that permits viral persistence despite antiretroviral therapy.[14][107][108] Viral factors further influence chronic progression, notably through genotypic differences and intra-host variability. Genotype 3 HEV exhibits greater quasispecies diversity in the capsid's M and P domains during acute infection, with higher nucleotide entropy and genetic distances predicting chronic outcomes by enabling antigenic variation and immune escape under selective pressure (e.g., lower Ka/Ks ratios indicate purifying selection favoring persistent variants). Genotype 4, while less commonly zoonotic in Western settings, demonstrates slower viral clearance in some immunocompromised hosts, potentially due to similar quasispecies dynamics, though chronic cases remain rarer than with genotype 3.[109][6] The timeline of progression is marked by prolonged viremia, defined as detectable HEV RNA beyond 3 months post-infection, which signals a high likelihood of chronicity and histological damage; by 6 months, it is formally classified as chronic. This persistence drives liver fibrosis, with studies showing Ishak fibrosis scores exceeding 3 in approximately 20% of untreated cases within the first year, progressing to bridging fibrosis or early cirrhosis in up to 67% by 2 years in severe instances. Recent genetic analyses of chronic strains highlight evolutionary constraints, where host gene insertions in the HVR promote adaptation for persistence but limit overall genomic diversification due to bottlenecks in immunocompromised environments, underscoring the virus's constrained path to chronicity.[6][110][111][112] Factors influencing severity The severity of hepatitis E virus (HEV) infection varies widely, with an overall case-fatality rate of 0.5-4% in the general population globally, though this rises dramatically to 20-30% among pregnant women, particularly in the third trimester.[1][6] Host factors play a critical role in determining outcomes. Advanced age, especially over 50 years, is associated with increased acute severity, particularly for genotypes 3 and 4 prevalent in developed regions, due to diminished immune responses and higher rates of symptomatic disease.[2] Pre-existing liver disease, such as chronic hepatitis or cirrhosis, markedly elevates the risk of acute-on-chronic liver failure, with mortality rates reaching up to 70%.[6] In endemic areas of low- and middle-income countries, malnutrition exacerbates disease progression by impairing immune function and increasing susceptibility to fulminant hepatitis.[46][113] Viral factors also influence severity. HEV genotypes 1 and 2, which predominate in endemic regions of Asia and Africa, are linked to higher mortality rates compared to genotypes 3 and 4, often due to their association with large-scale waterborne outbreaks and more aggressive acute hepatitis.[6][44] Additionally, a high viral inoculum dose correlates with greater liver injury, as demonstrated in primate models where larger doses led to more pronounced hepatic damage and clinical manifestations.[114] Environmental and co-morbid factors further modulate disease course. Co-infections, such as with hepatitis A virus, can amplify severity, leading to acute liver failure in rare cases through synergistic hepatic stress.[115] Pregnancy acts as a significant amplifier of severity, independent of genotype, likely due to hormonal and immunological changes that promote viral replication and fulminant outcomes.[1][3] Genetic elements contribute to inter-individual variability. Host polymorphisms in interferon (IFN) signaling pathways, including type I IFN immunity genes, are enriched in symptomatic cases and impair antiviral responses, increasing the likelihood of severe acute hepatitis.[116] Recent studies highlight HEV's genetic adaptations to human hosts, such as insertions in genotype 3 strains that enhance replication efficiency and potentially worsen clinical outcomes in susceptible individuals; broadly neutralizing antibodies targeting conserved epitopes provide protective effects against severe disease.[78][100] Diagnosis Clinical evaluation Clinical evaluation of suspected hepatitis E begins with a detailed history to identify potential exposure risks and epidemiological context. Key elements include recent travel to endemic regions such as parts of Asia, Africa, or Latin America, where fecal-oral transmission via contaminated water is common; consumption of undercooked meat from animals like pigs or wild game, associated with zoonotic strains; and underlying immunosuppression, such as in organ transplant recipients or those on chemotherapy, which increases the risk of infection. The incubation period typically ranges from 2 to 10 weeks, with an average of 5 to 6 weeks following exposure.[1][6] Symptom assessment focuses on the prodromal phase, characterized by nonspecific signs such as mild fever, anorexia, nausea, vomiting, and abdominal pain lasting a few days, followed by icteric symptoms including jaundice, dark urine, and pale stools, which usually persist for 1 to 6 weeks. In acute cases, fatigue and malaise are prominent, while chronic infections in immunocompromised individuals often present with milder or absent symptoms, primarily fatigue, without typical fever or rash. Risk factors like pregnancy, particularly in the second or third trimester, warrant urgent evaluation due to heightened severity and mortality risk of 20-25%. Jaundice duration and overall symptom progression help gauge acuity.[1][6][13] Physical examination may reveal icteric sclera, right upper quadrant tenderness, and hepatomegaly in 10-85% of symptomatic cases, reflecting liver inflammation. Splenomegaly is rare and not a characteristic finding. In chronic or asymptomatic presentations, physical signs are often minimal or absent.[5][6] For patients with fulminant hepatitis E progressing to acute liver failure, the King's College criteria are applied to assess prognosis and guide triage for potential liver transplantation. These criteria for non-acetaminophen-induced acute liver failure include unfavorable etiology (such as hepatitis E), age greater than 40 years, duration of jaundice more than 7 days before encephalopathy, international normalized ratio (INR) greater than 6.5, or a combination of three or more factors like INR greater than 3.5, age over 40, jaundice over 7 days, and non-A, non-B hepatitis.[117] In outbreak settings, 2025 WHO protocols emphasize rapid clinical triage using case definitions for suspected hepatitis E, integrating history of exposure in endemic areas with acute jaundice or elevated liver enzymes to prioritize cases for further investigation and resource allocation.[118] Serological and molecular tests Serological tests for hepatitis E virus (HEV) primarily detect antibodies produced in response to infection, with anti-HEV IgM indicating acute or recent infection and anti-HEV IgG signifying past exposure or immunity. Anti-HEV IgM typ