Hepatitis E Virus (HEV)

What is hepatitis E virus?

Hepatitis E disease is a liver disease that arises from an individual’s infection with the hepatitis E virus (HEV). The genetic material of this virus is comprised of single-stranded RNA and lacks an envelope. Hepatitis E generally presents as acute icteric hepatitis, also known as acute viral hepatitis or AVH for brevity. AVH typically does not exhibit any specific symptoms, but in certain cases, it progresses to acute liver failure or ALF for brevity. ALF is frequently linked to heightened disease severity with manifestations and mortality beyond the liver. The infection of this virus is observed worldwide, but the highest incidence rates are associated with Asia and South Africa.

Hepatitis E virus (HEV) is currently a public health concern in both developed and developing countries. This virus is acknowledged as a common pathogen shared between humans and livestock and as one of the primary causes of acute viral hepatitis globally. Additionally, HEV infection can persist, leading to chronicity in individuals with compromised immune systems. The severity of the disease and mortality rates are typically higher in cases of chronic infection and in pregnant women with AVH. Mortality resulting from hepatitis E in the general population typically ranges from 0.2% to 4% and in 2015, approximately 44,000 individuals lost their lives due to HEV.

Conversely, the mortality rate for pregnant women and patients with chronic liver disease is estimated to be between 15 and 100 percent. Overall, HEV is regarded as the most prevalent cause of acute viral hepatitis worldwide and according to the World Health Organization (WHO) statistics, approximately 20 million new cases are reported annually. The primary mode of transmission for this virus is the consumption of water contaminated with feces. Hepatitis E typically gives rise to either acute or chronic infection. Acute hepatitis E is characterized by a short-lived infection and in most instances, the body’s immune system is capable of eliminating the virus independently. However, chronic hepatitis E is a rare form that may develop in individuals who have undergone organ transplants and are receiving immunosuppressive medication or in those with HIV whose immune system is compromised.

Hepatitis E virus symptoms

most individuals afflicted with hepatitis E infection do not exhibit distinct clinical symptoms. In developing countries, signs of HEV infection are commonly observed in adults between the ages of 15 and 44. The findings of multiple researches demonstrate that the symptoms of this disease typically manifest roughly 15 to 60 days subsequent to infection. Among the prevailing symptoms of HEV infection are as follows:

Loss of appetite
Fever
Feeling weak and tired
Abdominal pains
Nausea and vomiting
Muscle and joint pains
Hepatomegaly
Jaundiced skin
darkened urine
skin rashes

Ways of HEV transmission

Hepatitis E infection is observed in various regions across the globe, although its prevalence rate is higher in developing countries and low or middle income countries. The underlying cause for this discrepancy is the limited access to safe drinking water and inadequate health services. The primary and prevalent mode of HEV transmission is through the consumption of water contaminated with fecal matter. Additional modes of transmission for this virus encompass the consumption of raw or undercooked meat from animals infected with HEV. In general, this disease is transmitted within the community through three distinct pathways, namely:

Transmission via drinking of contaminated water
Transmission from mother to child (known as vertical or perinatal transmission)
Transmission through contact with blood or blood products infected with HEV
Transmission from animals to humans (either through direct contact with infected animals or through the consumption of their meat)
Acquisition of an infected transplanted organ

HEV infection prevalence

Hepatitis E virus exhibits a global distribution with two separate patterns of epidemiological distribution based on HEV genotypes. These patterns consist of endemic and sporadic disease. In regions where the disease is endemic, the majority of infections are caused by HEV1 (with a higher prevalence) and HEV2 (with a lower prevalence). Conversely, in areas where the disease follows a sporadic pattern, HEV infection is commonly caused by HEV3 (with a high prevalence) and HEV4 (with a lower prevalence) genotypes. HEV infection is prevalent in numerous developing countries such as India, Bangladesh, Africa, the Middle East, Central America and China, where it manifests as epidemic and endemic outbreaks through contaminated water, often associated with genotypes 1 and 2. Over the past two decades, there have been no reported outbreaks of hepatitis E. In developed countries, the observation of HEV infection in the population typically occurs among travelers returning from countries with a high prevalence and the pattern of infection is sporadic. The table below presents the prevalence rates of different genotypes in various countries.

	Region of Occurrence

hosts

genotype

West Africa, North Africa & Asia

Human (only)

HEV1 (I)

Asia, Africa & Mexico

Human (only)

HEV2 (II)

North America, South America, Europe, Asia, & Africa

Human, Swine, & several other animals

HEV3 (III)

Americas, Europe & Asia

Human, Swine, & several other animals

HEV4 (IV)

Hepatitis E virus structure

HEV is categorized as a member of the Hepeviridae family which is a diminutive, unenveloped, spherical virus with a diameter of approximately 32 to 34 nm. The genetic material of this virus is a single-stranded, positive-sense RNA and is encompassed by an icosahedral capsid. The HEV genome comprises about 7200 nucleotides and includes a 5′ UTR (27 to 35 nucleotides), three sporadic and partially overlapping ORFs (open reading frame) and a 3′ UTR sequence (65 to 74 nucleotides). The presence of a capped 5′ end is critical for the infectivity of the virus. Conversely, the 3′ end of the UTR in the virus genome is a non-coding region and serves a pivotal role as a cis-acting element in governing the translation and replication of the viral genome.

HEV contains three viral proteins each possessing distinct functions and characteristics. These viral proteins are encoded by three ORFs within the viral genome. ORF1 represents the largest coding region, spanning nearly two-thirds of the viral genome. This segment resides proximal to the 5′ UTR end and measures approximately 5000 nucleotides in length. It functions in viral replication and protein processing and encodes non-structural proteins such as methyltransferase, guanylyl transferase, papain-like cysteine protease, RNA helicase and RNA-dependent RNA polymerase. Within ORF1, there exists a non-coding and hypervariable region that exhibits notable genetic variation.

Conversely, discrepancies in genome size among different HFV strains are frequently observed within the ORF1 region. ORF2 encodes a viral capsid protein consisting of 660 amino acids that envelops the viral RNA genome. The capsid represents the exclusive structural protein that assembles as a highly organized multimer. ORF3 overlaps with two other ORFs and encodes a minute phosphoprotein encompassing 123 amino acids, which plays a critical role in replication and cytoskeleton synthesis. ORF1 and ORF2/ORF3 are demarcated by a junction region or JR for brevity, while ORF2 and ORF3 overlap and are transcribed as a bicistronic subgenomic mRNA.

Different genotypes of HEV

The Hepatitis E Virus (HEV) is known to have a minimum of four distinct genotypes. Genotypes 1 and 2 are exclusive to the human population. Conversely, genotypes 3 and 4 have been detected in a diverse range of animal species, such as pigs, wild boars and deer, without inducing illness. However, there have been instances where these genotypes have been shown to cause disease in humans.

Genotypes 1 and 2

Genotypes 1 and 2 are often more prevalent in developing countries due to lack of suitable drinking water. These genotypes are obligate human pathogens that are transmitted to humans through feces-contaminated water. HEV infection during pregnancy (especially in the third trimester) will lead to severe complications for the mother and fetus compared to other acute viral hepatitis. The mortality rate in children under 2 years of age with HEV is very high in Central Asia and East Africa. In most people with acute HEV, no symptoms are observed, but if symptoms occur, they are often non-specific and include anorexia, nausea, fatigue, myalgia and jaundice. The incubation period of these genotypes is about 40 days, and in the laboratory results, an increase in the level of serum bilirubin and liver enzymes is observed. Genotype 1 and 2 infections are involved in causing acute liver failure.

Genotypes 3 and 4

HEV3 and HEV4 genotypes, unlike types 1 and 2, can infect both humans and animals. Some animals such as pigs, deer and wild boars are the main reservoirs of HEV. Reports indicate that HEV genotype 4 infection occurs mainly in Southeast Asia, but recently cases have been reported in Western countries, including Belgium, Germany and France. HEV genotype 3 is the most common genotype of the disease that causes autochthonous (locally acquired) infection in developed countries. Genotype 3 and 4 infections are mostly transmitted through contaminated food. These foods include pork liver and sausage, oysters, green vegetables and strawberries. In addition, transmission of HEV genotypes 3 and 4 infection through transfusion of HEV-contaminated blood products (including red blood cells, platelets, and plasma) has also been reported in many Western countries (and some Asian countries). If the person has an immune system deficiency, the type 3 genotype can become chronic, in which the level of liver enzymes increases about 6 months after infection.

HEV diagnosis

Currently, there is a wide range of techniques available for the identification of the HEV virus, which can be classified into two categories: serological methods and molecular detection techniques.

Serological tests

Serological tests are employed to diagnose acute HEV infection by detecting specific anti-HEV antibodies, namely IgM and IgG. The incubation period for HEV infection typically spans between two to six weeks. During the time of diagnosis, both HEV RNA and anti-HEV IgM can be detected, followed by the presence of anti-HEV IgG antibodies. The identification of anti-HEV IgM antibody in serum serves as a vital marker for acute HEV infection. Although the presence of anti-HEV IgM antibodies is only temporary (lasting approximately three to four months), in some cases, it may persist for up to a year. HEV RNA can be detected three weeks after infection and is often detectable in stool samples four to six weeks thereafter. Enzyme immunoassay is the most widely utilized serological method for detecting IgG and IgM antibodies against HEV in diagnosing hepatitis E virus infection. It is important to note that the detection of anti-HEV IgM and an increase in the titer of anti-HEV IgG antibodies alone are insufficient for a diagnosis. Enzyme immunoassay is not only used to detect anti-HEV antibodies but also for the detection of HEV capsid antigen.

Molecular methods

Molecular methods represent another means of HEV virus detection, involving the identification of the virus RNA in the blood or stool sample of the patient. Considering that serological tests often yield negative results in acute and chronic HEV infections among patients with suppressed immune systems due to organ transplantation, it is advisable to employ molecular tests for diagnosing the infection. Among the commonly utilized molecular methods for detecting HEV, PCR-based techniques such as Real-Time PCR are noteworthy. These techniques frequently employ labeled primers and probes that are complementary to specific protected regions of the virus genome, including ORF1, ORF2 and ORF3.

Through these techniques, it becomes feasible to identify the genotypes that infect humans. However, it is important to highlight that the determination of HEV infection genotypes or subgenotypes is primarily employed for epidemiological purposes and their clinical significance remains undetermined. This type of PCR test serves as a powerful tool for detecting minuscule amounts of nucleic acids, exhibiting a remarkable sensitivity. Real-Time PCR is based on the continuous measurement of the fluorescence signals’ amplification or reduction resulting from the amplification of primers and probes during fragment amplification. In comparison to conventional PCR, where the analysis of results is conducted after the completion of the reaction and by running the samples on a gel, Real-Time PCR enables the simultaneous monitoring of amplicon amplification for each cycle.

HEV treatment

In most cases, the elimination of hepatitis E is accomplished by the body’s immune system. When discussing the treatment of HEV infection, the emphasis often lies on mitigating the severity of disease symptoms and their management. One pharmaceutical agent employed in the treatment of HEV infection is Ribavirin. This particular drug is classified as a guanosine analog and upon metabolism, it functions as a nucleotide analog in order to deplete intracellular guanosine triphosphate and subsequently impede RNA replication. Moreover, this drug acts through the inhibition of viral replication, while also playing a role in the augmentation of interferon-stimulating genes expression and mutagenesis. Consequently, ribavirin therapy may be considered in cases of severe acute hepatitis or acute chronic liver failure.

The findings of certain studies indicate that ribavirin is associated with rapid improvement of liver enzymes profile, as well as a reduction in HEV RNA levels in patients with genotype 1 and 3 HEV infections. In individuals with chronic HEV infection and concomitant immune system deficiencies, the initial stage necessitates immune system strengthening by means of reducing the dosage of immunosuppressive drugs and initiating antiretroviral treatment, all the while monitoring HEV RNA levels on a monthly basis for a duration of 3 months. If reducing the dosage of immunosuppressive drugs poses a risk to the patient, oral Ribavirin is prescribed for a period of 3 months.

Sofosbuvir is another pharmaceutical agent utilized in the treatment of hepatitis C virus, with its function being the reduction of HEV3 genotype. Interferon α (IFNα) represents an alternative treatment modality for chronic hepatitis E, exhibiting effectiveness in achieving a sustained viral response in patients who have undergone liver transplantation and those on hemodialysis.