Classification and properties of hepatotropic viruses
The biological properties of the viruses determine their transmission routes and clinical outcomes. All causative agents are divided into two fundamental groups:
- With a fecal-oral mechanism (hepatitis A and E). These are simple RNA-containing viruses lacking a supercapsid. They are highly immunogenic, which makes the infection self-limiting. The organism recognizes the threat and triggers apoptosis of infected hepatocytes, allowing for the careful clearance of tissues without the risk of transitioning to a chronic form.
- With a parenteral mechanism (hepatitis B, C, D). These are complex viruses possessing an outer envelope (moreover, the defective virus D borrows its supercapsid from virus B). They employ an "immune evasion" tactic and do not stimulate adequate apoptosis. This leads to prolonged persistence of viremia, a high risk of chronic progression, and, consequently, the probable development of cirrhosis and neoplastic processes.
Pathogenesis of liver damage
The leading role in liver tissue destruction is played by immune-mediated cytolysis. The immune system attacks infected cells in two stages: via a cellular response (NK cells and cytotoxic T lymphocytes) and a humoral one (macrophages carry out antibody-dependent cell-mediated cytotoxicity).
Hepatocyte death goes through strict sequential stages:
- Damage to the cell membrane and increased permeability.
- Ionic imbalance: potassium efflux, sodium and calcium influx.
- Intracellular metabolic shifts and cell swelling.
- Destruction of intracellular membranes.
- Hydrolytic autolysis — rupture of lysosomes with the release of enzymes that break down proteins and nucleic acids.
Massive cell death provokes the development of mesenchymal inflammation. Kupffer cells are activated, pro-inflammatory cytokines are released, and plasma exudation into the stroma occurs. Laboratory confirmation of this process includes elevated transaminases (primarily ALT) and an increased thymol turbidity test due to the synthesis of acute-phase proteins.
Clinical manifestations and syndromes
The course of acute viral hepatitis is based on a combination of intoxication signs and local liver damage. Intoxication syndrome is most pronounced in the pre-icteric period and directly reflects the strength of the immune response.
Variants of the pre-icteric period course:
- Influenza-like: fever, chills, body aches, weakness.
- Dyspeptic: loss of appetite, nausea, epigastric pain, diarrhea.
- Asthenovegetative: normal body temperature, marked somnolence, irritability, dizziness.
- Mixed: a combination of various symptoms.
- Arthralgic: characteristic of parenteral hepatitis, occurs due to capillary damage by circulating immune complexes (CIC).
During the icteric period, intoxication often subsides, but jaundice syndrome (the result of cytolysis and impaired bilirubin excretion) and cholestasis syndrome come to the fore. Intrahepatic cholestasis develops due to the toxic suppression of transporter proteins and physical compression of the bile ducts by the edematous stroma. Clinically, it manifests as persistent jaundice, acholic stools, dark urine, and agonizing pruritus.
Acute liver failure and complications
In cases of extensive liver tissue necrosis (massive cytolysis), the organ drastically decreases in size, and the patient faces life-threatening complications—acute hepatocellular failure. Its essence lies in the global failure of hepatocyte functions:
- Impaired detoxification: urea synthesis is blocked, and blood ammonia levels rise sharply. This neurotoxin becomes the main culprit in the development of acute hepatic encephalopathy.
- Failure of protein-synthetic function: a sharp drop in the production of blood clotting factors leads to hemorrhagic syndrome (hemorrhages, a drop in the prothrombin index).
- Decreased albumin levels: hypoalbuminemia (marked by a drop in the sublimate test) leads to a decrease in the oncotic pressure of the blood. In combination with toxin accumulation and secondary hyperaldosteronism, this triggers severe edematous-ascitic syndrome.
Briefly: answers to topical questions
Through what mechanisms do parenteral hepatitis viruses (B, C, D) evade the immune response?
Sources for acute viral hepatitis with a parenteral transmission mechanism (B, C, D) indicate the following "immune evasion" mechanisms:
- viruses have a complex antigenic structure prone to mutations;
- they insufficiently initiate apoptosis of infected cells, which prevents the body from rapidly clearing the pathogen;
- characterized by prolonged, often lifelong persistence of the virus in the body;
- extraphepatic viral replication is possible.
For HCV, the following are additionally described:
- extrahepatic localization in lymph nodes, bone marrow, and spleen;
- replication within monocytes and other immune cells with impaired function and cellular cooperation;
- T-cell anergy due to genetic heterogeneity of the virus, high mutation rates, rapid replication rates, and lymphotropism;
- ineffective humoral response: antibodies are produced in excess but have minimal virus-neutralizing potential and do not protect against reinfection.
For hepatitis B virus, the mechanism of persistence and latency is also described: integration of the viral genome into the host cell DNA without the expression of viral antigens on the membrane.
Which serological markers (antigens and antibodies) confirm the diagnosis of acute viral hepatitis B?
Confirmation of acute viral hepatitis B is carried out by detecting specific HBV markers:
- HBsAg;
- HBeAg;
- anti-HBc IgM.
For differential diagnosis with viral hepatitis, the detection of HBV viral DNA is also indicated.
How do ALT and AST activity differ in viral hepatitis, and what is the de Ritis ratio?
Differences in aminotransferase activity are due to their intracellular topography, which makes it possible to assess the severity of liver damage. The de Ritis ratio reflects the proportion of these enzymes.
| Characteristic | ALT | AST |
|---|---|---|
| Localization | Exclusively in the cell cytoplasm | Has cytoplasmic and mitochondrial fractions |
| Dynamics | Cleared from the bloodstream more slowly | Mitochondrial fraction enters the blood in severe damage |
Acute viral liver damage is characterized by a predominance of ALT, with a de Ritis ratio of less than 1.
The variants of the pre-icteric period are easy to remember by the acronym GADS: Influenza-like (Grippopodobny), Asthenovegetative (Astenovegetativny), Dyspeptic (Dispepsichesky), Mixed (Smeshanny).
What else to study on this topic
- Features of taking an epidemiological history (Anamnesis vitae and incubation periods)
- Interpretation of serological markers for hepatitis A, B, C, D, E
- Pathogenesis of acute hepatic encephalopathy (AHE) and the role of hyperaldosteronism
- Diagnostic algorithms and nosological classification of mixed hepatitis
- Principles of pathogenetic therapy and indications for hospitalization
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