Hepatitis D virus - Classification, Morphology, Replication, Transmission, Pathogenesis, Lab diagnosis

Classification of Hepatitis D virus

The classification of the Hepatitis D virus is done:

Realm: Ribozyviria

Family: Kolmioviridae

Genus: Deltavirus

The Deltavirus genome contains species:

• Deltavirus cameroonense [HDV-7]

• Deltavirus carense [HDV-6]

• Deltavirus italiense [HDV-1]

• Deltavirus japanense [HDV-2]

• Deltavirus peruense [HDV-3]

• Deltavirus senegalense [HDV-8]

• Deltavirus taiwanense [HDV-4]

• Deltavirus togense [HDV-5]

Hepatitis D virus is an incomplete virus and requires the presence of HBV to replicate and infect other hepatocytes. Hence, HDV infection occurs only in patients who suffer from HBV infection.

Morphology of Hepatitis D virus

The Hepatitis D virus is spherical, enveloped (85nm in diameter), and single-stranded negative RNA of 17 kb size.

The single-stranded RNA is circular and is surrounded by a delta-antigen core which in turn is surrounded by an envelope that contains HBsAg. Delta Ag occurs in 2 sizes-small (24KDa) or large (26KDa). Delta Ag is the only protein coded for Hepatitis D virus RNA that is distinct from antigenic determinants of HBV.

Replication of Hepatitis D virus

Replication occurs in the liver, causing liver damage and cytotoxicity. The damage is caused as a result of direct cytopathic effect in combination with underlying immunopathology of HBV disease

Although the Hepatitis D virus can replicate independently within the hepatocytes, it requires HbsAgfor its propagation.

Transmission of Hepatitis D virus

Hepatitis D virus is a blood pathogen and is transmitted by blood and vaginal secretions. Transmission routes include:

• non-percutaneous route (close intimate contact)

• contaminated blood and blood products

• Sharing of contaminated needles among IV drug users

• sex

• perinatal

Pathogenesis of Hepatitis D virus

The incubation period of the Hepatitis D virus is 21-45 days but may be shorter in case of superinfection. The clinical course may range from acute-self-limited infection to acute fulfillment of liver failure. Clinically, Hepatitis D virus infection is indistinguishable from other forms of viral hepatitis.

Patients with both Hepatitis B virus and Hepatitis D virus infection show a more severe course of disease than patients with HBV infection alone. Only 1% of patients with coinfection progress to develop fulfillment hepatitis resulting in more rapid progression to cirrhosis.

Lab diagnosis of Hepatitis D virus

The laboratory diagnosis of Hepatitis D virus is as follows:

Specimen

Blood (serum)

Serological

ELISA is one of the serological tests used for diagnosis of Hepatitis D virus.

• IgM ELISA is used to detect anti-HDV IgM during the early stage of infection

• IgG ELISA for anti-HDV IgG is used during the later course of infection

Molecular

- Reverse Transcriptase PCR (RT-PCR) detects Hepatitis D virus RNA in blood in the stage of co-infection

*In superinfections, a high level of both IgM and IgGAb, as well as a high level of HDAg and Hepatitis D virus RNA, is demonstrated.