Pathogen Group and the Nature of the Delta Virus
Parenteral viral hepatitis pathogens traditionally include hepatitis viruses B, C, D, and G. Hepatitis B virus (HBV) is classified into a separate, major category, while the other agents are grouped under blood-borne infections.
The most unconventional member of this group is the hepatitis D virus (HDV). To this day, this infectious agent remains unclassified. Its key biological characteristic is that it is a defective virus. For successful replication within a host organism, it absolutely requires a helper virus, which is HBV.
Morphology and Antigenic Structure
The HDV virion is spherical with a diameter of only 36 nanometers. Its genetic material is represented by a negative-sense single-stranded circular RNA.
The core of the viral particle contains the specific HDc antigen (also known as the delta antigen). It consists of two protein molecules with polypeptide chains of different lengths that perform crucial regulatory functions:
- One protein actively stimulates the synthesis of the viral genome.
- The other protein inhibits this synthesis, providing control over replication.
The virus lacks its own outer envelope. To form one, it utilizes the surface HBs antigen of the hepatitis B virus. Several HDV genotypes circulate in nature (with genotype 1 predominating), but all form a single serotype.
Pathogenesis and Clinical Courses
The reservoir of the pathogen consists exclusively of hepatitis B virus carriers. The mechanism of transmission is identical to that of HBV infection. Once inside the body, the delta virus is not found in free circulation in the blood—its active replication occurs strictly inside hepatocytes (liver cells).
The prognosis of the disease critically depends on the type of infection:
- Coinfection: Simultaneous primary infection with hepatitis B and D viruses. Typically, this presents with a moderate clinical course.
- Superinfection: Develops when the hepatitis D virus infects a patient who already has chronic hepatitis B. This is the most dangerous scenario, causing a severe worsening of the disease with a high risk of acute liver failure and cirrhosis.
Diagnosis, Treatment, and Prevention
Modern laboratory practice uses two key approaches to confirm the diagnosis:
- Serological method: Enzyme-linked immunosorbent assay (ELISA) detects specific antibodies against HDV antigens in blood serum.
- Molecular biological method: Polymerase chain reaction (PCR) detects viral RNA directly.
Treatment of delta infection is complex and relies on interferon-based regimens. As for prevention, there is no specific vaccine against HDV alone. However, vaccination against hepatitis B automatically protects against hepatitis D, as the defective virus cannot exist without the HBs antigen.