Autochthonous hepatitis E in developed countries and HEV/HIV coinfection

Genetic diversity of hepatitis E virus (HEV) in imported and domestic camels in Saudi Arabia

Camels gained attention since the discovery of MERS-CoV as intermediary hosts for potentially epidemic zoonotic viruses. DcHEV is a novel zoonotic pathogen associated with camel contact. This study aimed to genetically characterize DcHEV in domestic and imported camels in Saudi Arabia. DcHEV was detected by RT-PCR in serum samples, PCR-positive samples were subjected to sequencing and phylogenetic analyses. DcHEV was detected in 1.77% of samples with higher positivity in domestic DCs. All positive imported dromedaries were from Sudan with age declining prevalence. Domestic DcHEV sequences clustered with sequences from Kenya, Somalia, and UAE while imported sequences clustered with one DcHEV isolate from UAE and both sequences clustered away from isolates reported from Pakistan. Full-genome sequences showed 24 amino acid difference with reference sequences. Our results confirm the detection of DcHEV in domestic and imported DCs. Further investigations are needed in human and camel populations to identify DcHEV potential zoonosis threat.

Acute and Persistent Hepatitis E Virus Genotype 3 and 4 Infection: Clinical Features, Pathogenesis, and Treatment

Hepatitis E virus (HEV) genotype (gt)3 and 4 infections are prevalent in industrialized and high-income countries. Although most HEV gt3 and gt4 infections are clinically silent, acute infection may be symptomatic in some patients. In persons with underlying liver disease and in elderly men, HEV infections may present as acute or acute-on-chronic liver failure. Chronic hepatitis may develop in immunosuppressed individuals, including transplant recipients, human immunodeficiency virus (HIV)-infected patients, and persons with hematologic malignancy undergoing chemotherapy, and may progress to life-threatening liver cirrhosis. Extrahepatic manifestations of infection may include neurological and renal disease. Although there is no approved specific therapy for the treatment of acute or chronic HEV gt3 or gt4 infection, off-label use of ribavirin appears to be capable of eliminating chronic HEV infection, and may reduce disease severity in patients suffering from acute liver failure.

Chronic Hepatitis E in Rheumatology and Internal Medicine Patients: A Retrospective Multicenter European Cohort Study

Objectives: Hepatitis E virus (HEV) infection is a pandemic with regional outbreaks, including in industrialized countries. HEV infection is usually self-limiting but can progress to chronic hepatitis E in transplant recipients and HIV-infected patients. Whether other immunocompromised hosts, including rheumatology and internal medicine patients, are at risk of developing chronic HEV infection is unclear. Methods: We conducted a retrospective European multicenter cohort study involving 21 rheumatology and internal medicine patients with HEV infection between April 2014 and April 2016. The underlying diseases included rheumatoid arthritis (n = 5), psoriatic arthritis (n = 4), other variants of chronic arthritis (n = 4), primary immunodeficiency (n = 3), systemic granulomatosis (n = 2), lupus erythematosus (n = 1), Erdheim–Chester disease (n = 1), and retroperitoneal fibrosis (n = 1). Results: HEV infection lasting longer than 3 months was observed in seven (33%) patients, including two (40%) patients with rheumatoid arthritis, three (100%) patients with primary immunodeficiency, one (100%) patient with retroperitoneal fibrosis and one (100%) patient with systemic granulomatosis. Patients with HEV infection lasting longer than 3 months were treated with methotrexate without corticosteroids (n = 2), mycophenolate mofetil/prednisone (n = 1), and sirolimus/prednisone (n = 1). Overall, 8/21 (38%) and 11/21 (52%) patients cleared HEV with and without ribavirin treatment, respectively. One patient experienced an HEV relapse after initially successful ribavirin therapy. One patient (5%) was lost to follow-up, and no patients died from hepatic complications. Conclusion: Rheumatology and internal medicine patients, including patients treated with methotrexate without corticosteroids, are at risk of developing chronic HEV infection. Rheumatology and internal medicine patients with abnormal liver tests should be screened for HEV infection.

Hepatitis E virus seroprevalence and determinants in various study populations in the Netherlands

BACKGROUND

The epidemiology of hepatitis E virus (HEV) is not fully understood. In this study, we assessed putative risk factors for HEV seropositivity in various study populations in the Netherlands.

METHODS

Data and samples from five different study populations were analysed: (A) blood donors (n = 5,239), (B) adults reporting a vegetarian life style since the age of 12 years (n = 231), (C) residents of Amsterdam, the Netherlands, with different ethnic backgrounds (n = 1,198), (D) men who have sex with men (MSM) (HIV positive and HIV negative) (n = 197), and (E) persons who use drugs (PWUD) (HIV positive and HIV negative) (n = 200). Anti-HEV immunoglobulin M (IgM) and immunoglobulin G (IgG) testing was performed using ELISA test (Wantai).

RESULTS

HEV IgM seroprevalence was low across all study populations (<1% to 8%). The age and gender-adjusted HEV IgG seroprevalence was 24% among blood donors (reference group) and 9% among the vegetarian group (adjusted Relative Risk [aRR]:0.36, 95%CI:0.23-0.57). Among participants of different ethnic backgrounds, the adjusted HEV IgG seroprevalence was 16% among participants with a Dutch origin (aRR:0.64, 95%CI:0.40-1.02), 2% among South-Asian Surinamese (aRR:0.07, 95%CI:0.02-0.29), 3% among African Surinamese (aRR:0.11, 95%CI:0.04-0.34), 34% among Ghanaian (aRR:1.53, 95%CI:1.15-2.03), 19% among Moroccan (aRR:0.75, 95%CI:0.49-1.14), and 5% among Turkish (aRR:0.18, 95%CI:0.08-0.44) origin participants. First generation Moroccans had a higher risk for being IgG HEV seropositive compared to second generation Moroccan migrants. The statistical power to perform these analyses in the other ethnic groups was too low. In the MSM group the IgG HEV seroprevalence was 24% (aRR:0.99, 95%CI:0.76-1.29), and among PWUD it was 28% (aRR:1.19, 95%CI:0.90-1.58). The number of sexual partners in the preceding six months was not significantly associated with IgG HEV seropositivity in MSM. The association between HIV status and HEV seropositivity was significant in PWUD, yet absent in MSM. HIV viral load and CD4 cell count were not associated with HEV seropositivity in HIV positive MSM and PWUD.

CONCLUSIONS

Vegetarians were significantly less often HEV seropositive. Ethnic origin influenced the risk for being IgG HEV seropositive. MSM and PWUD were not at higher risk for being IgG HEV seropositive than blood donors.

Autoimmune liver disease serology in acute hepatitis E virus infection

The etiology of autoimmune hepatitis (AIH) is unknown, though hepatotropic viruses may be potential triggers. Hepatitis E virus (HEV) infection, an increasingly recognized cause of acute hepatitis, has been misdiagnosed as AIH due to the occurrence of autoantibodies during its acute phase. It has also been suggested that HEV infection may lead to or unmask AIH. The HEV seroprevalence has been ascertained in patients with AIH, but the prevalence of AIH-related autoantibodies in patients with HEV infection has not been systematically tested. We aimed to investigate whether acute HEV infection is associated with the presence of AIH-relevant autoantibodies, following the liver autoimmune serology guidelines of the International AIH Group. We tested 48 patients with acute HEV infection. Half of them had at least one autoantibody, 17% two autoantibodies. Anti-nuclear antibody (ANA) were detected in 16 (33%), anti-smooth muscle antibody (SMA) in 10 (21%), and anti-neutrophil cytoplasmic antibody (ANCA) in 7 (14.6%). Of note, two patients showed SMA with VG or VGT patterns and five had ANA with homogeneous appearance, both being typical of AIH type 1. Other AIH-specific autoantibodies were negative. Atypical anti-mitochondrial antibody, without evidence of primary biliary cholangitis, was positive in one patient, disappearing at follow-up. Follow-up (median 12 months) serum was available from seven autoantibody positive patients: two became negative, while five remained positive, although no patient developed AIH to date. In conclusion, autoantibodies are frequently present during acute HEV infection, indicating that HEV should always be excluded before diagnosing AIH. Importantly, a minority of patients with acute hepatitis E develops AIH-specific autoantibodies, and, though they did not progress to autoimmune liver disease in the short-term, they warrant long-term monitoring.

Hepatitis E: prevention and treatment

PURPOSE OF REVIEW

Infection with the hepatitis E virus (HEV) is very common worldwide. The epidemiology, viral genotypes, and transmission routes differ between low-resource countries and economically developed countries. These differences have resulted in the design of diverse prevention and treatment strategies to combat HEV.

RECENT FINDINGS

The population seroprevalence of HEV immunoglobulin G varies between 5 and 50%. However, the diagnosis of acute hepatitis from HEV has not been common in the United States or Western Europe. Chronic progressive HEV infections have been reported among patients who are immunocompromised. Successful treatment of patients with chronic hepatitis from HEV infection with antiviral agents, such as ribavirin or interferon-α, has been reported. Extrahepatic manifestations of HEV infection are common. Large epidemics of hundreds or thousands of cases continue to be reported among populations in Asia and Africa. A subunit peptide HEV vaccine has been found to be highly efficacious in a large clinical trial. However, the vaccine has not been evaluated in populations of pregnant women or other risk groups and is only available in China.

SUMMARY

Although HEV infections are increasingly recognized as a global public health problem, there are few methods for prevention and treatment that are widely available.

Hepatitis E virus: Western Cape, South Africa

AIM

To conduct a prospective assessment of anti-hepatitis E virus (HEV) IgG seroprevalence in the Western Cape Province of South Africa in conjunction with evaluating risk factors for exposure.

METHODS

Consenting participants attending clinics and wards of Groote Schuur, Red Cross Children’s Hospital and their affiliated teaching hospitals in Cape Town, South Africa, were sampled. Healthy adults attending blood donor clinics were also recruited. Patients with known liver disease were excluded and all major ethnic/race groups were included to broadly represent local demographics. Relevant demographic data was captured at the time of sampling using an interviewer-administered confidential questionnaire. Human immunodeficiency virus (HIV) status was self-disclosed. HEV IgG testing was performed using the Wantai^® assay.

RESULTS

HEV is endemic in the region with a seroprevalence of 27.9% (n = 324/1161) 95%CI: 25.3%-30.5% (21.9% when age-adjusted) with no significant differences between ethnic groups or HIV status. Seroprevalence in children is low but rapidly increases in early adulthood. With univariate analysis, age ≥ 30 years old, pork and bacon/ham consumption suggested risk. In the multivariate analysis, the highest risk factor for HEV IgG seropositivity (OR = 7.679, 95%CI: 5.38-10.96, P < 0.001) was being 30 years or older followed by pork consumption (OR = 2.052, 95%CI: 1.39-3.03, P < 0.001). A recent clinical case demonstrates that HEV genotype 3 may be currently circulating in the Western Cape.

CONCLUSION

Hepatitis E seroprevalence was considerably higher than previously thought suggesting that hepatitis E warrants consideration in any patient presenting with an unexplained hepatitis in the Western Cape, irrespective of travel history, age or ethnicity.

Acute Hepatitis E: Two Sides of the Same Coin

The relevance of acute hepatitis E virus (HEV) infections has been underestimated for a long time. In the past, HEV infection had been interpreted falsely as a disease limited to the tropics until the relevance of autochthonous HEV infections in the Western world became overt. Due to increased awareness, the incidence of diagnosed autochthonous HEV infections (predominantly genotype 3) in industrialized countries has risen within the last decade. The main source of infections in industrialized countries seems to be infected swine meat, while infections with the tropical HEV genotypes 1 and 2 usually are mainly transmitted fecal-orally by contaminated drinking water. In the vast majority of healthy individuals, acute HEV infection is either clinically silent or takes a benign self-limited course. In patients who develop a symptomatic HEV infection, a short prodromal phase with unspecific symptoms is followed by liver specific symptoms like jaundice, itching, uncoloured stool and darkened urine. Importantly, tropical HEV infections may lead to acute liver failure, especially in pregnant women, while autochthonous HEV infections may lead to acute-on-chronic liver failure in patients with underlying liver diseases. Immunosuppressed individuals, such as transplant recipients or human immunodeficiency virus (HIV)-infected patients, are at risk for developing chronic hepatitis E, which may lead to liver fibrosis and cirrhosis in the long term. Importantly, specific treatment options for hepatitis E are not approved by the regulation authorities, but off-label ribavirin treatment seems to be effective in the treatment of chronic HEV-infection and may reduce the disease severity in patients suffering from acute liver failure.

Hepatitis E: latest developments in knowledge

Hepatitis E, caused by Hepatitis E virus (HEV), is a highly prevalent disease in developing countries. In developed nations, autochthonous HEV infections seem to be an emergent disease. Its clinical manifestations and epidemiology are well known for endemic countries. It has been confirmed that hepatitis E is a zoonosis and that parenteral transmission can also occur. The molecular mechanisms of HEV replication are not fully understood, mostly because there are no efficient cell culture systems. HEV can cause chronic hepatitis in organ transplant recipients and immunocompetent patients. Cases with fulminant hepatitis and other extrahepatic manifestations have also been reported. The diagnosis is based on serological studies and detection of HEV RNA in blood and feces. Treatment with ribavirin and/or pegylated-IFN-α have proven to be successful in some cases. The recently approved/marketed vaccine is a good option in order to prevent this infection.

Acute and Chronic Hepatitis E Virus Infection in Human Immunodeficiency Virus-Infected U.S. Women

Exposure to hepatitis E virus (HEV) is common in the United States, but there are few data on prevalence of HEV/human immunodeficiency virus (HIV) coinfection in U.S.

POPULATIONS

We tested 2,919 plasma samples collected from HIV-infected (HIV(+)) women and men enrolled in U.S. cohort studies for HEV viremia using a high-throughput nucleic acid testing (NAT) platform. NAT(+) samples were confirmed by real-time polymerase chain reaction. Samples were selected for testing primarily on the basis of biomarkers of liver disease and immune suppression. Prevalence of HEV viremia was 3 of 2,606 and 0 of 313 in tested plasma samples collected from HIV(+) women and men, respectively. All HEV isolates were genotype 3a. Based on follow-up testing of stored samples, 1 woman had chronic HEV infection for >4 years whereas 2 women had acute HEV detectable at only a single study visit.

CONCLUSIONS

To our knowledge, this is the first reported case of chronic HEV infection in an HIV(+) U.S. individual. We also confirm that chronic HEV infection can persist despite a CD4(+) count >200 cells/mm(3). Overall, though, these data suggest that HEV infection is rare in the HIV(+) U.S. population.

Hepatitis E virus in patients with decompensated chronic liver disease: a prospective UK/French study

BACKGROUND

In developed countries, hepatitis E is a porcine zoonosis caused by hepatitis E virus (HEV) genotype 3. In developing countries, hepatitis E is mainly caused by genotype 1, and causes increased mortality in patients with pre-existing chronic liver disease (CLD).

AIM

To determine the role of HEV in patients with decompensated CLD.

METHODS

Prospective HEV testing of 343 patients with decompensated CLD at three UK centres and Toulouse France, with follow-up for 6 months or death. IgG seroprevalence was compared with 911 controls.

RESULTS

11/343 patients (3.2%) had acute hepatitis E infection, and three died. There were no differences in mortality (27% vs. 26%, OR 1.1, 95% CI 0.28-4.1), age (P = 0.9), bilirubin (P = 0.5), alanine aminotransferase (P = 0.06) albumin (P = 0.5) or international normalised ratio (P = 0.6) in patients with and without hepatitis E infection. Five cases were polymerase chain reaction (PCR) positive (genotype 3). Hepatitis E was more common in Toulouse (7.9%) compared to the UK cohort (1.2%, P = 0.003). HEV IgG seroprevalence was higher in Toulouse (OR 17, 95% CI 9.2-30) and Truro (OR 2.5, 95% CI 1.4-4.6) than in Glasgow, but lower in cases, compared to controls (OR 0.59, 95% CI 0.41-0.86).

CONCLUSIONS

Hepatitis E occurs in a minority of patients with decompensated chronic liver disease. The mortality is no different to the mortality in patients without hepatitis E infection. The diagnosis can only be established by a combination of serology and PCR, the yield and utility of which vary by geographical location.

Cryptic Hepatitis B and E in Patients With Acute Hepatitis of Unknown Etiology

BACKGROUND

Up to 30% of acute viral hepatitis has no known etiology. To determine the disease etiology in patients with acute hepatitis of unknown etiology (HUE), serum specimens were obtained from 38 patients residing in the United Kingdom and Vietnam and from 26 healthy US blood donors. All specimens tested negative for known viral infections causing hepatitis, using commercially available serological and nucleic acid assays.

METHODS

Specimens were processed by sequence-independent complementary DNA amplification and next-generation sequencing (NGS). Sufficient material for individual NGS libraries was obtained from 12 HUE cases and 26 blood donors; the remaining HUE cases were sequenced as a pool. Read mapping was done by targeted and de novo assembly.

RESULTS

Sequences from hepatitis B virus (HBV) were detected in 7 individuals with HUE (58.3%) and the pooled library, and hepatitis E virus (HEV) was detected in 2 individuals with HUE (16.7%) and the pooled library. Both HEV-positive cases were coinfected with HBV. HBV sequences belonged to genotypes A, D, or G, and HEV sequences belonged to genotype 3. No known hepatotropic viruses were detected in the tested normal human sera.

CONCLUSIONS

NGS-based detection of HBV and HEV infections is more sensitive than using commercially available assays. HBV and HEV may be cryptically associated with HUE.

Long-term efficacy of a hepatitis E vaccine

BACKGROUND

Hepatitis E virus (HEV) is a leading cause of acute hepatitis. The long-term efficacy of a hepatitis E vaccine needs to be determined.

METHODS

In an initial efficacy study, we randomly assigned healthy adults 16 to 65 years of age to receive three doses of either a hepatitis E vaccine (vaccine group; 56,302 participants) or a hepatitis B vaccine (control group; 56,302 participants). The vaccines were administered at 0, 1, and 6 months, and the participants were followed for 19 months. In this extended follow-up study, the treatment assignments of all participants remained double-blinded, and follow-up assessments of efficacy, immunogenicity, and safety were continued for up to 4.5 years.

RESULTS

During the 4.5-year study period, 60 cases of hepatitis E were identified; 7 cases were confirmed in the vaccine group (0.3 cases per 10,000 person-years), and 53 cases in the control group (2.1 cases per 10,000 person-years), representing a vaccine efficacy of 86.8% (95% confidence interval, 71 to 94) in the modified intention-to-treat analysis, rather than (95% confidence interval, 71 to 84) [corrected]. Of the participants who were assessed for immunogenicity and were seronegative at baseline, 87% of those who received three doses of the hepatitis E vaccine maintained antibodies against HEV for at least 4.5 years; HEV antibody titers developed in 9% in the control group. The rate of adverse events was similar in the two groups.

CONCLUSIONS

Immunization with this hepatitis E vaccine induced antibodies against HEV and provided protection against hepatitis E for up to 4.5 years. (Funded by the Chinese Ministry of Science and Technology and others; ClinicalTrials.gov number, NCT01014845.).

Mystery of hepatitis e virus: recent advances in its diagnosis and management

Mysterious aspects of the long presumed to be well-known hepatitis E virus (HEV) have recently surfaced that distinguish it from other hepatotropic viruses. It is a cause of chronic hepatitis in immunosuppressed patients. It has human to human transmission through blood and mantains high seroprevalence in blood donors. HEV has also been found to occur more frequently in the West in those without a history of travel to endemic countries. It has varied extrahepatic manifestations and has multiple non-human reservoirs including pigs and rats. Considering these recent discoveries, it appears odd that HEV is not sought more frequently when working up acute and chronic hepatitis patients. The disease is particularly severe among pregnant women and has a high attack rate in young adults. What adds to its ambiguity is the absence of a well-established diagnostic criteria for its detection and that there is no specific antiviral drug for hepatitis E, except for isolated cases where ribavirin or pegylated interferon alpha has been used with occasional success. This review paper discusses the recent advances in the knowledge of the virus itself, its epidemiology, diagnostic approach and prevention, and the treatment options available.

High prevalence of antibodies against hepatitis E virus in HIV-infected patients with unexplained liver disease

OBJECTIVE

To look for evidence of hepatitis E virus (HEV) exposure in HIV-infected patients with unexplained elevations of liver stiffness (LS).

METHODS

Case-control study conducted in 31 HIV-infected patients with unexplained elevations of LS and in 31 HIV-controls with normal LS, matched by age, sex and CD4 cell-counts. Serum HEV antibodies were tested by two ELISA procedures and by Immunoblot. We defined exposure to HEV as the detection of serum HEV antibodies by at least one of the two ELISA assays, provided that it was confirmed by Immunoblot. A real-time PCR RNA assay was conducted in all plasma samples to identify subjects with active HEV infection.

RESULTS

Exposure to HEV was demonstrated, according to the criteria used in this study, in 9 (29%) of the cases, whereas it was shown in 5 (16%) of the controls (p=.3). Serum HEV RNA was detected in none of the controls and in only in one case. This patient had a documented chronic hepatitis E with progression to cirrhosis.

CONCLUSIONS

HEV antibodies are frequently found in HIV-infected patients with unexplained liver disease.

Estimation of hepatitis E virus (HEV) pig seroprevalence using ELISA and Western blot and comparison between human and pig HEV sequences in Belgium

Zoonotic transmission of hepatitis E virus (HEV) is of special concern, particularly in high income countries were waterborne infections are less frequent than in developing countries. High HEV seroprevalences can be found in European pig populations. The aims of this study were to obtain prevalence data on HEV infection in swine in Belgium and to phylogenetically compare Belgian human HEV sequences with those obtained from swine. An ELISA screening prevalence of 73% (95% CI 68.8-77.5) was determined in Belgian pigs and a part of the results were re-evaluated by Western blot (WB). A receiver operating characteristic curve analysis was performed and scenarios varying the ELISA specificity relative to WB were analysed. The seroprevalences estimated by the different scenarios ranged between 69 and 81% and are in agreement with the high exposure of the European pig population to HEV. Pig HEV sequences were genetically compared to those detected in humans in Belgium and a predominance of genotype 3 subtype f was shown in both swine and humans. The high HEV seroprevalence in swine and the close phylogenetic relationships between pig and human HEV sequences further support the risk for zoonotic transmission of HEV between humans and pigs.

Hepatitis E: an emerging disease

Currently, the infection with the hepatitis E virus represents the most frequent cause for acute hepatitis and jaundice in the world. According to WHO estimations, around two billion people, representing one third of the world's population, live in endemic areas for HEV and, therefore, are at risk of infection. In developed countries, the circulation of the virus in both human and animal (swine, boar, deer) sewage has been confirmed; however, the incidence rate is low compared to that of developing countries where outbreaks of acute hepatitis transmitted via the fecal-oral route are originated, more frequently in the flooding season or after natural disasters, combined with deficient sanitary conditions. There are currently 4 known genotypes of HEV. Genotypes 1 and 2 are isolated in all human epidemic outbreaks in developing countries, while genotypes 3 and 4 are isolated not only in humans but also in animals, in both developing and industrialized countries. These data support genotypes 3 and 4 having zoonotic nature. The diagnosis of this disease is based in the detection of anti-HEV IgG and IgM in blood serum using enzyme-linked immunosorbent methods. However, the method that best confirms the diagnosis is the RT-PCR, which detects HEV RNA in blood serum and also provides the genotype. The clinical course is generally that of an acute hepatitis which in some cases may require hospitalization and that, in transplant patients or HIV infected individuals can become a chronic hepatitis. Furthermore, the virus constitutes an important risk for pregnant women. The hepatitis E can present a wide range of symptoms, from a subclinical case to chronic liver disease with extrahepatic manifestations. For this reason, the diagnostic is challenging if no differential diagnosis is included. There is no specific antiviral drug for hepatitis E, but satisfactory results have been observed in some patients treated with pegylated interferon alfa2a and/or ribavirin. This revision is an update of all the molecular, epidemiological, clinic and preventive knowledge on this emergent disease up to date.

Host immune status and response to hepatitis E virus infection

Hepatitis E virus (HEV), identified over 30 years ago, remains a serious threat to life, health, and productivity in developing countries where access to clean water is limited. Recognition that HEV also circulates as a zoonotic and food-borne pathogen in developed countries is more recent. Even without treatment, most cases of HEV-related acute viral hepatitis (with or without jaundice) resolve within 1 to 2 months. However, HEV sometimes leads to acute liver failure, chronic infection, or extrahepatic symptoms. The mechanisms of pathogenesis appear to be substantially immune mediated. This review covers the epidemiology of HEV infection worldwide, the humoral and cellular immune responses to HEV, and the persistence and protection of antibodies produced in response to both natural infection and vaccines. We focus on the contributions of altered immune states (associated with pregnancy, human immunodeficiency virus [HIV], and immunosuppressive agents used in cancer and transplant medicine) to the elevated risks of chronic infection (in immunosuppressed/immunocompromised patients) and acute liver failure and mortality (among pregnant women). We conclude by discussing outstanding questions about the immune response to HEV and interactions with hormones and comorbid conditions. These questions take on heightened importance now that a vaccine is available.

Protective immunity against HEV

Rural community of Dongtai City in eastern China is endemic for hepatitis E virus (HEV), with the zoonotic genotype 4 virus predominating. The virus appears to be widely distributed in environment at generally low levels, such that infection is common, but >97% of which are asymptomatic and provoke a modest antibody response. Naturally acquired immunity affords 75% protection against infection, prevents disease caused by primary infection and alleviates severity of the disease caused by the residual infection that had evaded host immune surveillance. The protection, however, is extended to a minority, while leaving the majority of population essentially without the benefits of immune protection. Vaccination affords similar level of protection as does natural immunity, but expands the protective coverage to the entire population.