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Hepatitis viruses (excluding hepatitis C virus) 

Hepatitis viruses (excluding hepatitis C virus)

Chapter:
Hepatitis viruses (excluding hepatitis C virus)
Author(s):

N.V. Naoumov

DOI:
10.1093/med/9780199204854.003.070521_update_001

Update:

Eight genotypes of HDV now reported.

Update on HEV (including chronic disease) reported in transplant recipients.

Updated on 31 May 2012. The previous version of this content can be found here.
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date: 27 March 2017

The group of hepatitis viruses includes five unrelated human viruses (A to E), which differ in their genome organization, biology, and epidemiology, while being united by their hepatotropism. About 10 to 15% of cases of viral hepatitis are considered as non-A to E hepatitis, whose aetiology is still unknown, but the search for which has led to the identification of several new viruses (e.g. HGV or GB virus-C, TT, and SEN viruses) of uncertain pathogenic significance.

Clinical aspects of viral hepatitis are discussed in Chapter 15.21.1.

Hepatitis A virus (HAV)

A single-stranded RNA virus with four genotypes in humans. HAV replicates primarily in hepatocytes and is excreted via the biliary system into the faeces, where it can be found in high concentrations prior to clinical symptoms. HAV causes acute hepatitis with significant morbidity and occasional mortality. Anti-HAV IgG remains detectable after acute infection and provides protective immunity.

Hepatitis B virus (HBV)

HBV is the smallest human DNA virus. Eight genotypes, designated A to H, have been determined, each having a distinct geographical distribution. The virus is noncytopathic, with virus-specific cellular immunity being the main determinant for the outcome of infection. Eradication of HBV is rare, but in cases with resolution of HBV infection an effective immune response controls HBV replication and there is no liver disease. The natural evolution of chronic infection includes four consecutive phases: (1) early ‘immunotolerant’ phase—high levels of virus replication and minimal liver inflammation; (2) immune reactive phase—significant hepatic inflammation and elevated serum aminotransferases; with some patients progressing to (3) ‘non-replicative’ phase—seroconversion to anti-HBe; undetectable or low level of viraemia (below 2000 IU/ml by polymerase chain reaction-based assays); resolution of hepatic inflammation; and (4) HBeAg-negative chronic hepatitis B—due to the emergence of viral mutations; characterized by fluctuating serum HBV DNA and serum ALT levels, and progressive liver disease.

Hepatitis C virus (HCV)

See Chapter 7.5.22.

Hepatitis delta virus (HDV)

A defective virus with a single-stranded circular RNA genome. Eight genotypes have been determined in humans; genotype 1 is most common in the Western world and genotype 2 is predominant in East Asia. HDV infection is always associated with HBV infection and occurs as a consequence of coinfection or superinfection. Clinical manifestations vary from acute to fulminant hepatitis and from an asymptomatic carrier state to progressive chronic liver disease. Diagnosis is based on the detection of serum HDag and serum HDV RNA. The optimal treatment of HDV is uncertain. Prevention is by vaccination against HBV.

Hepatitis E virus (HEV)

A single-stranded RNA virus. HEV is widely distributed and transmitted by the faeco-oral route and may be zoonotic, with evidence of infection in pigs, cattle and sheep in endemic regions. It causes acute viral hepatitis which may be fulminant in those who are pregnant, malnourished or have existing liver disease. Chronic infection has been reported in transplant recipients. Immunity can be transient and may wane if acquired in childhood. An effective vaccine has been developed but is not yet commercially available.

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