Chapter Notes: Hepatitis Viruses

Table of Contents
1. Learning objectives
2. Introduction
3. Classification and overview of hepatitis viruses
4. Hepatitis A virus (HAV) - infectious hepatitis
5. Hepatitis B virus (HBV) - serum hepatitis
6. Hepatitis C virus (HCV)
7. Hepatitis D virus (HDV) - delta agent
8. Hepatitis E virus (HEV)
9. Hepatitis G virus (HGV; GBV-C)
10. Key public-health points and prevention
11. Summary of important historical and scientific points
12. Key points (concise)
13. Indications for hepatitis B vaccination
14. Important questions
15. Further reading
View more

Learning objectives

• Classify the recognised hepatitis viruses.
• Compare and tabulate differences between the main hepatitis viruses.
• Compare important features of hepatitis A virus (HAV) and hepatitis B virus (HBV).
• Describe the morphology, antigenic structure, modes of transmission and carrier state of hepatitis B virus.
• Explain laboratory diagnosis of hepatitis B virus infection and the markers used.
• Discuss prophylaxis of hepatitis B infection, including available vaccines and passive immunisation.
• Describe hepatitis C virus (HCV), hepatitis D virus (HDV, delta agent), hepatitis E virus (HEV) and hepatitis G virus (HGV): their properties, clinical features, diagnosis, prophylaxis and treatment where relevant.

Introduction

Viral hepatitis is a systemic disease that primarily involves the liver. At least six distinct agents-hepatitis A, B, C, D (delta), E and G-are recognised as hepatitis viruses. Although the liver is the principal target organ for these agents, they differ markedly in structure, genome type, mode of replication, routes of transmission, clinical course, and long-term consequences. Some hepatitis-like illnesses remain unexplained and are referred to as non-A to E hepatitis.

Classification and overview of hepatitis viruses

Major hepatitis agents and brief features:

Hepatitis A virus (HAV) - infectious hepatitis

Properties and discovery

Feinstone and colleagues (1973), using immune electron microscopy (IEM), detected HAV particles in faeces from experimentally infected human volunteers. Sensitive serological assays and polymerase chain reaction (PCR) methods allow detection of HAV in stools and clinical samples and measurement of specific antibodies in serum. Chimpanzees and some other primates are susceptible experimentally. HAV is the only human hepatitis virus that can be readily cultivated in certain human and simian cell cultures and has been cloned.

Morphology

HAV is a small non-enveloped icosahedral virus, about 27-30 nm in diameter, with a single-stranded positive-sense RNA genome and structural proteins that form the capsid. It belongs to the family Picornaviridae (genus Hepatovirus). Only one serotype is recognised.

Resistance and inactivation

HAV is relatively stable in the environment and resists acid, some solvents and moderate heat. It is inactivated by:

• Autoclaving (121°C for 20 minutes) and boiling for ≥5 minutes.
• Dry heat at 180°C for 1 hour.
• Ultraviolet irradiation under adequate exposure.
• Formalin and chlorine at sufficient concentrations (10-15 ppm chlorine for 30 minutes in water; higher concentrations for disinfection of surfaces where required).

HAV can survive prolonged storage at refrigeration temperatures and in contaminated water or foodstuffs.

Pathogenesis

HAV is ingested and replicates in the intestinal epithelium or oropharynx before entering the bloodstream. A short viraemic phase precedes liver localisation. The virus replicates in hepatocytes and Kupffer cells; it is released into bile and shed in faeces in large quantities-often from about 10 days before clinical jaundice appears until shortly after. HAV replicates without obvious cytopathic effects; liver injury appears to be largely immune-mediated. Chronic infection does not occur.

Epidemiology

Transmission is faecal-oral via contaminated water, food, or close personal contact. Shellfish taken raw from contaminated water (clams, oysters, mussels) frequently cause outbreaks. In areas with poor sanitation, infection is commonly acquired in early childhood and by adulthood most persons have anti-HAV antibodies and are immune.

Clinical features

Incubation period: 2-6 weeks (commonly 15-45 days). Disease in children is often asymptomatic or mild; adults more commonly have symptomatic illness. Typical course:

• Prodromal (pre-icteric) phase with fever, malaise, anorexia, nausea, vomiting and right upper-quadrant tenderness.
• Icteric phase with jaundice, dark urine and pale stools; symptomatic improvement often follows the appearance of jaundice.
• Recovery over weeks; convalescence may be prolonged for 4-6 weeks. Relapse can occur but fulminant hepatitis is rare, except among older persons.

Laboratory diagnosis

Diagnosis is by detection of virus or specific antibody:

• Virus visualisation: Immune electron microscopy of faecal extracts can detect HAV particles during late incubation and pre-icteric phases.
• Antibody detection: The diagnostic test for acute infection is IgM anti-HAV by ELISA or other immunoassays. IgM anti-HAV appears in late incubation, peaks in 2-3 weeks and disappears after 3-4 months. IgG anti-HAV appears around the same time, peaks in 3-4 months and persists long term, indicating past infection and immunity.
• Virus isolation: HAV can be grown in some cell culture systems but routine virus isolation is uncommon; molecular detection by PCR is used in research and outbreak tracing.

Prophylaxis and immunisation

General measures

Prevent transmission by ensuring safe drinking water, good sanitation, hand hygiene and avoiding raw shellfish from contaminated waters. Chlorination of drinking water at recommended levels inactivates HAV.

Immunisation

Because HAV has a single serotype and infects only humans, immunisation is effective:

• Passive immunoprophylaxis: Human pooled immunoglobulin (IM) given before exposure or early in the incubation period can prevent or attenuate illness but may not prevent infection or viral excretion. Dose is adjusted by product guidance.
• Active immunisation: Inactivated HAV vaccines (formalin inactivated, adsorbed to alum) produced in human diploid cell culture are safe and effective for children and adults at risk (e.g., travellers to endemic areas). Typical schedule: two IM doses; protection begins about 4 weeks after the first dose and persists for many years. Live attenuated HAV vaccines have been developed and used in some countries.

Treatment

Treatment is supportive and symptomatic. No specific antiviral therapy is currently recommended for routine HAV infection.

Hepatitis B virus (HBV) - serum hepatitis

Importance

HBV is one of the most significant hepatitis viruses worldwide. It can establish chronic infection, particularly when acquired in infancy, and chronic HBV infection is an important cause of cirrhosis and hepatocellular carcinoma. Vaccination against HBV reduces chronic infection and the subsequent risk of liver cancer.

Classification

HBV belongs to the family Hepadnaviridae. Two genera are recognised in this family: Orthohepadnavirus (mammalian hepadnaviruses, including HBV) and Avihepadnavirus (avian hepatitis viruses).

Structure and particles

HBV virions (Dane particles) are roughly 42 nm in diameter and are enveloped. The envelope contains hepatitis B surface antigen (HBsAg). Inside the envelope is a 27 nm nucleocapsid (core) that contains hepatitis B core antigen (HBcAg) and the viral genome. Three types of particles can be seen in serum of infected individuals:

• 22 nm spherical particles (non-infectious), composed of HBsAg.
• Filamentous/tubular particles (22 nm diameter, variable length), composed of HBsAg.
• 42 nm Dane particle (complete virion) composed of envelope (HBsAg) and inner nucleocapsid (HBcAg) containing viral DNA and polymerase.

Blumberg first identified the "Australia antigen" (later shown to be HBsAg) in 1965; its association with serum hepatitis was established by 1968. The Dane particle was described by Dane in 1970.

Antigenic components

• HBsAg (surface antigen): Envelope proteins, including major S protein; present in virion envelope and in excess as 22 nm particles in serum.
• HBcAg (core antigen): Located in the nucleocapsid; not usually detectable free in serum.
• HBeAg (e antigen): A soluble, non-particulate protein related to HBcAg; its presence in serum indicates active viral replication and high infectivity.

Genome and gene products

The HBV genome is a partially double-stranded circular DNA. It is compact and encodes overlapping reading frames for multiple proteins, including:

• S gene (surface proteins: S, Pre-S2, Pre-S1 regions producing small, middle and large surface proteins)
• C gene (core and precore regions producing HBcAg and HBeAg)
• P gene (polymerase with reverse transcriptase and RNase H activities)
• X gene (HBx protein, a transcriptional transactivator associated with enhanced viral replication)

Although a DNA virus, HBV replicates via an RNA intermediate using reverse transcription carried out by its polymerase.

HBsAg subtypes and antigenic variation

HBsAg contains a common group antigen "a" and type-specific determinants encoded as combinations of d/y and w/r. The major subtypes are adw, adr, ayw and ayr. Subtype distribution has geographical patterns and may assist epidemiological tracing, but does not greatly affect immunity because the common "a" determinant is shared.

Replication and extrahepatic presence

HBV replicates in hepatocytes. The replication cycle involves transcription of viral RNA, reverse transcription to DNA within the core, and assembly of virions. HBV DNA and proteins have also been detected in extrahepatic tissues (bone marrow, lymphoid tissues), though the significance is not fully understood.

Stability

HBV is relatively stable in the environment and can remain infectious on surfaces for prolonged periods. It is inactivated by strong disinfectants (e.g., hypochlorite solutions) and appropriate heat and chemical treatment. HBsAg may sometimes persist after the infectious agent is inactivated; therefore antigen persistence does not always reflect infectivity.

Clinical syndromes

Acute infection

Incubation period is typically 1-6 months. The onset is often insidious with prodromal symptoms (fever, malaise, anorexia) progressing to jaundice and hepatic signs. Fulminant hepatitis occurs in a small percentage and may be fatal. Immune complex phenomena (rash, arthritis, vasculitis, glomerulonephritis) can occur.

Convalescence and outcome

About 90-95% of immunocompetent adults recover clinically within 1-2 months. Mortality is generally low (0.5-2%), higher in certain settings such as post-transfusion hepatitis. A small proportion may develop fulminant hepatitis.

Chronic infection and sequelae

Between about 1% and 10% of infected adults become chronic carriers (higher in those infected as infants). Chronic infection can progress to chronic hepatitis, cirrhosis and hepatocellular carcinoma over decades.

Pathogenesis

Hepatocyte injury is mainly immune-mediated: the cellular immune response (cytotoxic T lymphocytes, NK cells) directed against infected hepatocytes causes liver inflammation and clinical hepatitis. Inadequate immune response can permit persistent viral replication and carrier state. Infants are more likely to become chronically infected because of immature immune responses.

Epidemiology

HBV is distributed worldwide. Areas of high endemicity (carrier frequency 10-20%) include parts of East and Southeast Asia, the Pacific Islands and sub-Saharan Africa. Intermediate prevalence areas (2-10%) include parts of the Indian subcontinent and Eastern Europe. Low prevalence (<1%) occurs="" in="" many="" western="" european="" countries,="" australia,="" new="" zealand,="" canada="" and="" the="" usa.="" transmission="" patterns="" vary="" with="" socioeconomic="" conditions:="" perinatal="" and="" early="" childhood="" transmission="" are="" important="" in="" high-prevalence="" areas,="" whereas="" sexual="" and="" parenteral="" transmission="" predominate="" in="" low-prevalence="">

Modes of transmission

1. Parenteral: exposure to infected blood and body fluids-blood transfusion (before screening), contaminated needles and syringes, sharps injuries, reuse of instruments (tattooing, piercings).
2. Perinatal (vertical): transmission from HBsAg/HBeAg-positive mothers to infants during birth; breastfeeding is not a significant route if mother and infant receive appropriate prophylaxis.
3. Sexual: transmission via semen and vaginal secretions; risk increases with number of partners and high-risk sexual practices.

Hepatitis B carriers

Persons with persistent HBsAg in serum are considered carriers. Two broad categories are:

• Super carriers: HBsAg-positive with HBeAg present, high viral titres and high infectivity (HBV DNA detectable at high levels).
• Simple carriers: HBsAg-positive without HBeAg, low or undetectable HBV DNA levels, lower infectivity. Many super carriers evolve into simple carriers over time.

HBV markers and their interpretation

Serological markers are used to diagnose stage of infection and infectivity. Key markers:

• HBsAg: first marker to appear after infection; indicates current infection or carrier state.
• Anti-HBs: antibody to surface antigen; denotes recovery and immunity (or immunity after vaccination).
• Anti-HBc IgM: marker of recent/acute infection.
• Anti-HBc IgG: indicates past or chronic infection.
• HBeAg: indicates active viral replication and high infectivity; anti-HBe suggests lower infectivity.
• HBV DNA and DNA polymerase activity measured by PCR or hybridisation: indicate viral replication and are used to monitor chronic infection and response to therapy.

Laboratory diagnosis

Diagnosis combines serology and molecular tests:

• ELISA/RIA for HBsAg, HBeAg, anti-HBc (IgM/IgG), anti-HBe and anti-HBs.
• HBV DNA detection and quantification by PCR or hybridisation-based methods to assess replication and monitor therapy.
• Biochemical tests: serum aminotransferases (ALT and AST) rise markedly in acute hepatitis; bilirubin is elevated in icteric illness.

Prophylaxis

General measures

Avoid high-risk behaviours (unprotected sex with multiple partners, injection drug use), ensure safe transfusion practices, use universal precautions in healthcare settings, and implement safe injection and instrument sterilisation procedures.

Passive immunisation

Hepatitis B immune globulin (HBIG) provides immediate passive protection. HBIG (300-500 IU IM depending on product and exposure) should be given as soon as possible after significant exposure (preferably within 48 hours). A second dose may be given per guidelines; if the exposed person is unvaccinated, HBIG is often given together with a vaccine series at separate injection sites.

Active immunisation (vaccines)

• Plasma-derived vaccine (historic): prepared from HBsAg purified from carrier plasma; now largely superseded because of availability of recombinant vaccines.
• Recombinant yeast-derived vaccine (current standard): HBsAg produced in Saccharomyces cerevisiae; given with alum adjuvant. Usual schedule: three IM doses at 0, 1 and 6 months. Seroconversion rates ≈90% in healthy adults; long-term protection is substantial; boosters are generally needed only for high-risk groups.
• CHO cell-derived recombinant vaccines and vaccines including Pre-S1/Pre-S2 antigens: available in some settings and may improve early seroconversion.
• Experimental approaches: synthetic peptide vaccines and recombinant live-vector vaccines have been investigated.

Treatment

There is no universally effective specific therapy for acute HBV infection beyond supportive care. For chronic HBV, antiviral agents (nucleos(t)ide analogues such as lamivudine, entecavir, tenofovir) and interferon-alpha are used to suppress viral replication and reduce progression. HBIG is used for post-exposure prophylaxis and for newborns of HBsAg-positive mothers together with vaccination.

Hepatitis C virus (HCV)

Properties

HCV is an enveloped positive-sense ssRNA virus of the family Flaviviridae (genus Hepacivirus). Particle size is about 50-60 nm. The HCV genome encodes a polyprotein that is processed to structural (core, E1, E2) and non-structural proteins (NS3, NS4, NS5, etc.). HCV shows considerable genetic diversity, classified into multiple genotypes and subtypes that influence epidemiology and response to therapy.

Mode of infection and epidemiology

Transmission is mainly parenteral: blood transfusion (especially before blood screening), contaminated needles (injection drug use), and contaminated medical equipment. Vertical and sexual transmission are possible but less efficient. HCV occurs worldwide and infects only humans.

Clinical course

Incubation period 15-160 days (mean ≈50 days). HCV may cause:

• Acute hepatitis (≈15% of cases resolve spontaneously).
• Chronic hepatitis (≈70%), with risk of progression to cirrhosis and hepatocellular carcinoma over decades.
• Rapid progression to cirrhosis in a subset (≈15%).

Laboratory diagnosis

Diagnosis relies on serology and molecular detection:

• Anti-HCV by ELISA (various generations of assays using multiple antigens); confirmatory immunoblot (where recommended).
• HCV RNA detection by RT-PCR or other nucleic acid amplification tests for early diagnosis, detection in seronegative patients and quantification (viral load) for treatment monitoring.

Prophylaxis and treatment

No vaccine is available. Prevention focuses on blood screening, safe injection practices and harm-reduction for injection-drug users. Treatment options have evolved rapidly: interferon-alpha with ribavirin was historically used; direct-acting antiviral agents (DAAs) now allow high cure rates for most genotypes (regimens are genotype-dependent and subject to national guidelines).

Hepatitis D virus (HDV) - delta agent

Discovery and nature

HDV was identified in 1977 by Rizzetto and colleagues as a novel antigen in liver biopsies from HBV-infected patients experiencing severe disease. HDV is a defective satellite virus: a small circular single-stranded RNA (≈1,700 nucleotides) that requires HBV for replication and for acquisition of its envelope (HBsAg). HDV therefore occurs only in persons co-infected with HBV or superinfecting HBV carriers.

Morphology

HDV particles are spherical, about 36-37 nm, and are enveloped by HBsAg. The delta genome is circular single-stranded RNA that encodes a single major protein (delta antigen).

Types of infection and clinical significance

• Coinfection - simultaneous acquisition of HBV and HDV: presents as acute hepatitis and can be severe or fulminant.
• Superinfection - HDV infection in a person chronically infected with HBV: commonly causes more severe and rapidly progressive hepatitis, and is associated with an increased risk of fulminant disease and chronicity.

HDV infection commonly worsens the course of HBV-related liver disease; prevention of HBV prevents HDV.

Laboratory diagnosis

HDV diagnosis is by detection of anti-delta antibodies (IgM/IgG) by ELISA, detection of delta antigen, or by HDV RNA using molecular probes and PCR.

Treatment and prophylaxis

No specific antiviral therapy is reliably effective for HDV. Interferon-alpha has been used with limited success in some cases. Prevention relies on prevention of HBV infection (HBV vaccination protects against HDV).

Hepatitis E virus (HEV)

Properties

HEV is a non-enveloped, 27-34 nm positive-sense ssRNA virus classified in the family Hepeviridae (genus Orthohepevirus). Only one major serotype is recognised among human strains.

Epidemiology and transmission

HEV is transmitted faecal-orally, primarily via contaminated water supplies. It causes epidemic and sporadic acute hepatitis in less-developed regions and is a major cause of enterically transmitted non-A, non-B hepatitis.

Clinical features

Incubation period 2-9 weeks (average ≈6 weeks). HEV causes acute self-limiting hepatitis similar to HAV, but with higher mortality (≈1-2% overall) and markedly higher mortality in pregnant women (≈15-25% in some epidemics). HEV infection in pregnancy is associated with maternal mortality, miscarriage and perinatal death.

Laboratory diagnosis

• Exclude HAV and HBV by appropriate serology (IgM anti-HAV and HBsAg/anti-HBc).
• IgM and IgG anti-HEV by ELISA.
• HEV RNA detection in faeces or acute sera by RT-PCR.
• Immunoelectron microscopy can visualise calicivirus-like particles in faeces during outbreaks.

Prophylaxis

Control depends on provision of clean water, sanitation and good hygiene. Recombinant vaccines have been developed and used in some countries and show promise; widespread use varies by region.

Hepatitis G virus (HGV; GBV-C)

Overview

Isolates originally named GB viruses (GBV-A, GBV-B, GBV-C) include GBV-C, which is closely related to HGV. HGV (GBV-C) is a flavivirus-like blood-borne agent identified in persons with hepatitis and in transfusion recipients. Its role in human liver disease remains unclear; many infected persons have no obvious liver disease while others with HGV infection have acute or chronic hepatitis where no other cause is apparent.

Diagnosis

• Detection of HGV (GBV-C) RNA by RT-PCR indicates active viremia.
• Anti-HGenv (anti-E2) antibodies may develop with clearance of viremia.

Clinical significance

HGV is transmitted in blood and is found worldwide. Chronic viremia may persist for years; the causal role in chronic hepatitis and hepatocellular carcinoma is not established.

Key public-health points and prevention

• Hepatitis A and E are primarily enterically transmitted and controlled by improved sanitation, safe water and food hygiene.
• HBV, HCV and HGV are principally blood-borne; prevention requires safe blood transfusion practices, safe injection techniques, harm-reduction for injection drug users, and safe sexual practices.
• HBV vaccination is the most effective preventive measure to reduce chronic HBV infection and HBV-related hepatocellular carcinoma; HBV immunisation of neonates and infants is a cornerstone of control programmes.
• Passive immunoglobulin preparations (HAV immunoglobulin, HBIG) provide short-term protection after exposure.
• Screening of blood donors for HBsAg, anti-HCV and nucleic acid testing has substantially reduced transmission by transfusion.

Summary of important historical and scientific points

• Feinstone et al. (1973) demonstrated HAV by immune electron microscopy.
• Blumberg discovered the "Australia antigen" (HBsAg) in 1965; association with serum hepatitis was shown by 1968.
• Dane described the complete HBV virion (Dane particle) in 1970.
• Rizzetto and colleagues identified the delta antigen (HDV) in 1977.

Key points (concise)

• At least six hepatitis viruses (A, B, C, D, E and G) are well recognised.
• All hepatitis viruses are RNA viruses except HBV, which is a partially double-stranded DNA virus (Hepadnaviridae).
• Modes of transmission differ: enteric for HAV and HEV; parenteral, sexual and perinatal for HBV and HCV; HDV depends on HBV; HGV is blood-borne.
• HAV diagnosis: IgM anti-HAV by ELISA; HAV can be visualised in faeces by IEM historically.
• HBV: Dane particle (42 nm) contains HBsAg envelope and HBcAg core; key markers include HBsAg, HBeAg, anti-HBc IgM/IgG and HBV DNA.
• HBV prevention: HBIG for passive protection after exposure; active immunisation with recombinant HBV vaccine (0, 1, 6 months schedule) is highly effective.
• HCV: anti-HCV by ELISA and HCV RNA by RT-PCR; no vaccine, but antiviral therapy (direct-acting antivirals) can cure most infections.
• HDV: requires HBV for replication; prevention via HBV vaccination.
• HEV: faecal-oral transmission; serious in pregnancy; diagnosis by anti-HEV and HEV RNA; prevention by improved water sanitation and vaccines where available.
• HGV: blood-borne, detected by RNA assays; clinical significance remains uncertain.

Indications for hepatitis B vaccination

Vaccination is recommended for all infants and children and for adults in high-risk groups. It is indicated for neonates of HBsAg-positive mothers, healthcare workers, persons with multiple sexual partners, injection-drug users, patients requiring frequent blood transfusions or haemodialysis, and other at-risk groups. Vaccination of mothers and of infants reduces perinatal transmission and prevalence of chronic carriers, decreasing long-term complications such as hepatocellular carcinoma.

Important questions

1. Q: Name the hepatitis viruses. Describe the morphology and antigenic structure of hepatitis B virus.

2. Q: Classify hepatitis viruses. Discuss the laboratory diagnosis of infections caused by hepatitis B virus.

3. Q: Draw a neat labelled diagram of hepatitis B virus.

4. Q: Write short notes on:

   • Q: Hepatitis A virus (HAV).

   • Q: Hepatitis B virus or Dane's particle.

   • Q: Hepatitis B surface antigen (HBsAg) or Australia antigen.

   • Q: Hepatitis B virus markers.

   • Q: Hepatitis C virus (HCV).

   • Q: Hepatitis D virus or Delta agent.

   • Q: Non-A, Non-B hepatitis.

   • Q: Hepatitis E virus.

   • Q: Hepatitis G virus.

   • Q: Prophylaxis of hepatitis B or hepatitis B vaccine.

Further reading

• Fields Virology (selected chapters on hepatitis A, B, C, D and E).
• Hollinger FB, Emerson SU. Hepatitis A virus. In: Fields Virology.
• Hollinger FB, Liary TJ. Hepatitis B virus. In: Fields Virology.
• Hagedorn CH, Rice CM. The hepatitis C viruses. Curr Top Microbiol Immunol 2000;242:1-380.
• Hadler SC, Fields HA. Hepatitis delta virus. In: Textbook of Human Virology.
• Reyes GR, Baroudy BM. Molecular biology of NANBH agents: hepatitis C and hepatitis E viruses. Adv Virus Res 1991;40:57-102.
• Maillard ME, Gollan JR. Suppressing Hepatitis B. N Engl J Med 2003;348:848.