Hepatitis Virus

Hepatitis Virus
Introduction
Viral hepatitis is a systemic disease primarily involving the liver. Most cases of acute viral hepatitis in children and adults are caused by one of the following agents: hepatitis A virus (HAV), the etiologic agent of viral hepatitis type A (infectious hepatitis); hepatitis B virus (HBV), which is associated with viral hepatitis B (serum hepatitis); hepatitis C virus (HCV), the agent of hepatitis C (common cause of posttransfusion hepatitis); or hepatitis E virus (HEV), the agent of enterically transmitted hepatitis. Hepatitis viruses produce acute inflammation of the liver, resulting in a clinical illness characterized by fever, gastrointestinal symptoms such as nausea and vomiting, and jaundice. Regardless of the virus type, identical histopathologic lesions are observed in the liver during acute disease.


Properties of Hepatitis Viruses
The characteristics of the five known hepatitis viruses are shown in Table 1.


Table 1. Characteristics of Hepatitis Viruses.


Virus Hepatitis A Hepatitis B Hepatitis C Hepatitis D Hepatitis E
Family Picornaviridae Hepadnaviridae Flaviviridae Unclassified Unclassified
 
Genus Hepatovirus  Orthohepadnavirus  Hepacivirus  Deltavirus  Hepevirus 
Virion 27 nm, icosahedral 42 nm, spherical 60 nm, spherical 35 nm, spherical 30–32 nm, icosahedral
Envelope No Yes (HBsAg) Yes Yes (HBsAg) No
Genome ssRNA dsDNA ssRNA ssRNA ssRNA
Genome size 7.5 kb 3.2 kb 9.4 kb 1.7 kb 7.6 kb
Stability Heat- and acid-stable Acid-sensitive Ether-sensitive, acid-sensitive Acid-sensitive Heat-stable
Transmission Fecal-oral Parenteral Parenteral Parenteral Fecal-oral
Prevalence High High Moderate Low, regional Regional
Fulminant disease Rare Rare Rare Frequent In pregnancy
Chronic disease Never Often Often Often Never
Oncogenic No Yes Yes ? No


Hepatitis Type A
HAV is a distinct member of the picornavirus family . HAV is a 27- to 32-nm spherical particle with cubic symmetry, containing a linear single-stranded RNA genome with a size of 7.5 kb. Although it was first provisionally classified as enterovirus 72, the nucleotide and amino acid sequences of HAV are sufficiently distinct to assign it to a new picornavirus genus, Hepatovirus. Only one serotype is known. There is no antigenic cross-reactivity with HBV or with the other hepatitis viruses.
HAV is stable to treatment with 20% ether, acid (pH 1.0 for 2 hours), and heat (60 °C for 1 hour), and its infectivity can be preserved for at least 1 month after being dried and stored at 25 °C and 42% relative humidity or for years at -20 °C. The virus is destroyed by autoclaving (121 °C for 20 minutes), by boiling in water for 5 minutes, by dry heat (180 °C for 1 hour), by ultraviolet irradiation (1 minute at 1.1 watts), by treatment with formalin (1:4000 for 3 days at 37 °C), or by treatment with chlorine (10–15 ppm for 30 minutes). Heating food to > 85 °C (185 °F) for 1 minute and disinfecting surfaces with sodium hypochlorite (1:100 dilution of chlorine bleach) are necessary to inactivate HAV.
HAV initially was identified in stool and liver preparations by employing immune electron microscopy as the detection system . Sensitive serologic assays and polymerase chain reaction (PCR) methods have made it possible to detect HAV in stools and other samples and to measure specific antibody in serum.