Pathogen group and nature of the delta virus
The pathogens of parenteral viral hepatitis traditionally include hepatitis B, C, D, and G viruses. At the same time, hepatitis B virus (HBV) is isolated into an independent, comprehensive category, while the remaining pathogens are considered within a single group of bloodborne infections.
The most unusual representative of the group is hepatitis D virus (HDV). To date, this infectious agent remains unclassified. Its main biological characteristic is that it is a defective virus. For successful replication in the host organism, it absolutely requires a helper virus, which is HBV. Epidemiological observations show a predominance of this infection in Russia.
Morphology and antigenic structure
The HDV virion is spherical, and its diameter is only 36 nanometers. The genetic material is represented by a minus-strand of single-stranded circular RNA.
In the core of the viral particle is a specific HDc antigen (also known as delta antigen). It consists of two protein molecules with polypeptide chains of different lengths, which perform a crucial regulatory function:
- One of the proteins actively stimulates the synthesis of the viral genome.
- The second protein, on the contrary, inhibits this synthesis, providing control over replication.
The virus does not have its own outer envelope. To form it, it uses the surface HBs antigen of hepatitis B virus. Several HDV genotypes circulate in nature (the first one is dominant), but all of them form a single serotype.
Pathogenesis and clinical course variants
The reservoir of the pathogen consists exclusively of hepatitis B virus carriers. The transmission mechanism is completely identical to that of HBV infection. Once in the body, the delta virus is not detected in the blood in a free form — its active replication proceeds strictly inside hepatocytes (liver cells).
The prognosis of the disease critically depends on the infection variant:
- Coinfection. This is a simultaneous primary infection with hepatitis B and D viruses. As a rule, this variant leads to a moderate course of the infectious process.
- Superinfection. Develops when hepatitis D virus superimposes on chronic hepatitis B already existing in the patient. This is the most dangerous scenario, which causes a sharp worsening of the disease, carries a high risk of developing acute liver failure and forming cirrhosis.
Diagnostics, treatment, and prevention
To confirm the diagnosis in modern laboratory practice, two key approaches are used:
- Serological method. Using enzyme-linked immunosorbent assay (ELISA), specific antibodies to HDV antigens are determined in blood serum.
- Molecular biological method. The use of polymerase chain reaction (PCR) allows detecting the viral RNA itself directly in liver tissue biopsy specimens.
Therapy for delta infection is quite complex and is based on the use of interferon preparations. As for prevention, there is no specific vaccine against HDV itself. However, vaccination against hepatitis B automatically provides protection against hepatitis D as well, since without the presence of the HBs antigen, the defective virus cannot exist.
Briefly: answers to topical questions
Which classes of specific antibodies to HDV are determined in blood serum during serological diagnosis?
During serological diagnosis of viral hepatitis D by ELISA, specific antibodies are determined:
- class M antibodies (anti-HDV IgM);
- class G antibodies (anti-HDV IgG).
What specific transmission routes are typical for hepatitis D virus?
Hepatitis D virus is characterized by household, sexual, and vertical transmission routes. The sexual route occurs during hetero- and homosexual contacts, and the vertical route is from an infected mother to the fetus; in HDV infection, it occurs much less frequently than in isolated hepatitis B. In general, the mechanism and transmission routes are similar to those of viral hepatitis B.
What modern groups of antiviral drugs are used to treat hepatitis D?
The following modern groups of antiviral drugs are used to treat viral hepatitis D:
- Interferon preparations — used as baseline therapy.
- Viral entry inhibitors — this group includes bulevirtide, which is an NTCP receptor blocker.
Bulevirtide is the first and only targeted drug officially approved for the treatment of chronic viral hepatitis D in adult patients.
In which biological material of the patient is hepatitis D virus RNA determined by PCR?
Hepatitis D virus RNA is determined by PCR in liver biopsy specimens.
How many genotypes of hepatitis D virus are distinguished in modern classification?
Hepatitis D virus has three genotypes. All genotypes form a single serotype. Genotype 1 dominates; HDV-I prevails on the territory of the Russian Federation.
Coinfection — Company (viruses arrive together, moderate course). Superinfection — Superimposed (overlapped on chronic hepatitis, severe course).
Class and exam questions
Why is the hepatitis D virus called defective?
It lacks the ability to synthesize its own outer envelope. To form a complete virion, it requires the HBs antigen provided by a helper virus — hepatitis B.
Where does the pathogen localize in the human body?
Hepatitis D virus does not circulate in the bloodstream in a free state. The process of its replication takes place exclusively inside liver cells (hepatocytes).
How to protect yourself from infection if there is no vaccine for hepatitis D?
Since the virus cannot multiply without the HBs antigen, standard routine vaccination against hepatitis B provides complete immunity to delta infection as well.
What else to study on this topic
- Detailed characteristics of hepatitis B virus (HBV)
- Hepatitis C virus: structural features and pathogenesis
- Hepatitis G virus and its place in the structure of parenteral infections
- Mechanisms of replication of defective viruses in hepatocytes
- Specifics of using interferon preparations in viral hepatitis
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