Virus biology and epidemiology
Hepatitis D virus (HDV) is an RNA-containing pathogen belonging to the genus Deltavirus of the family Togaviridae. Its key biological feature is defectiveness. The virus is incomplete and completely incapable of autonomous replication.
To assemble new viral particles, it critically requires hepatitis B virus (HBV). The outer envelope (supercapsid) of the delta virus is constructed from the hepatitis B surface antigen — HBsAg. Because of this dependency, isolated infection (monoinfection) with hepatitis D virus is impossible: the disease manifests exclusively in HBsAg carriers.
The sole reservoir and source of infection is an infected human. The primary route of transmission is parenteral (via infected blood), but vertical transmission from an infected mother to child is also possible. It is believed that the virus exerts a direct damaging (cytopathic) effect on hepatocytes.
Coinfection: simultaneous infection
Coinfection occurs when a patient is simultaneously infected with both viruses (HBV and HDV). The incubation period in this case ranges from 8 to 10 weeks.
- Prodromal period: usually shortened. Patients are troubled by high fever and migratory pain in large joints (arthralgia).
- Icteric period: accompanied by pronounced intoxication and severe pain in the right upper quadrant (projection of the liver) or epigastrium.
Coinfection is often severe. There is a high risk of massive hepatic necrosis progressing to acute liver failure (hepatic coma). In a favorable scenario, the disease lasts 1.5–2 months, although protracted forms with clinical exacerbations are possible. The risk of chronicity is comparable to that of standard acute hepatitis B.
Serological profile: from the first days, a full set of markers is detected in the blood (HBV DNA, HDV RNA, HBsAg, HBeAg, HDV Ag antigen). After 3–4 weeks, early anti-HDV IgM antibodies appear, which disappear after a few months and are replaced by protective anti-HDV IgG antibodies.
Superinfection: secondary infection superimposed on existing one
Superinfection is the infection with the delta virus of a person already infected with the hepatitis B virus (a chronic hepatitis patient or carrier). This is the most unfavorable clinical course.
The incubation and prodromal periods are sharply shortened to just 3–5 days. The disease manifests abruptly: extremely high fever, repeated vomiting, pronounced intoxication, and pain.
Clinical and laboratory features of the icteric period:
- Intense jaundice (hyperbilirubinemia due to the direct fraction).
- Sharp rise in liver enzymes (high cytolytic activity).
- Pronounced hepatosplenomegaly and development of edema-ascites syndrome.
- Undulating course with frequent exacerbations.
In superinfection, there is an extremely high risk of developing a malignant (fulminant) form with a fatal outcome. Of interest is the phenomenon of viral interference: during prolonged co-replication, HDV suppresses hepatitis B virus. This is manifested by the disappearance of HBV DNA from the blood and seroconversion of HBeAg to anti-HBe, while active replication of HDV RNA persists.
Principles of treatment and prevention
Treatment tactics for viral hepatitis D are based on the same principles as the therapy for viral hepatitis B.
Non-specific prevention aims to interrupt the parenteral route of transmission. It includes mandatory testing of all blood products for HBV and HDV markers, as well as the use of exclusively disposable medical instruments.
Specific prevention relies on the pathogen's dependence on the surface antigen. Since the delta virus cannot exist without HBsAg, the most effective prevention measure against HDV is universal vaccination of the population against hepatitis B. Established immunity to HBV automatically protects a person from HDV infection.
The formula of incompleteness: D does not live without B. No HBsAg — no delta infection.
Class and exam questions
Can you get hepatitis D if you do not have hepatitis B?
No, this is completely impossible. Hepatitis D virus is defective; for the formation of its outer envelope, the hepatitis B virus surface antigen (HBsAg) is critically required.
How does superinfection differ from coinfection?
Coinfection is simultaneous infection with two viruses at once, whereas superinfection is the superimposition of hepatitis D virus on chronic hepatitis B already present in the body. Superinfection proceeds significantly more severely.
How does viral interference work in hepatitis D?
In superinfection, the delta virus actively suppresses the reproduction of hepatitis B virus. As a result, HBV DNA disappears from the blood, but the replication of HDV itself continues at a high level.
What else to study on this topic
- Detailed decoding of the dynamics of serological markers in HDV.
- Mechanisms of the direct cytopathic effect of HDV on hepatocytes.
- Features of the pathogenesis of the fulminant form and the development of hepatic coma.
- Differential diagnosis between coinfection and superinfection based on laboratory data.
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