Viral hepatitis A, B, C, D, E cause acute hepatocellular necrosis and portal inflammation. Immune-mediated hepatocyte killing dominates. HAV and HEV typically resolve; HBV, HCV, HDV often progress to chronic infection with persistent necroinflammation, fibrosis, and eventual cirrhosis.
From your study of acute inflammation, you know that the inflammatory response is a double-edged sword: it contains and eliminates threats, but the same mechanisms that kill pathogens also damage surrounding tissue. From viral replication, you know that viruses co-opt host cellular machinery to reproduce, inserting their genetic material and using host ribosomes, enzymes, and membranes. Viral hepatitis represents the collision of these two processes inside the liver—and understanding why some infections resolve while others persist requires thinking carefully about how the immune system recognizes and responds to hepatocyte infection.
A key insight is that most liver damage in viral hepatitis is immune-mediated, not directly cytopathic. The hepatitis viruses themselves are not particularly toxic to hepatocytes—they replicate within them, but don't immediately destroy them. The damage comes when cytotoxic T lymphocytes (CD8+ T cells) recognize viral antigens displayed on infected hepatocyte surfaces and kill those cells, and when the inflammatory cascade recruits macrophages, natural killer cells, and neutrophils that release reactive oxygen species and proteases. This is why ALT and AST (liver enzymes that spill into the blood when hepatocytes are damaged) are the primary markers of viral hepatitis: elevated transaminases reflect the extent of immune-mediated hepatocyte killing, not simply the viral load. The inflammatory infiltrate visible histologically in the portal tracts and lobules is the liver's immunological battle zone.
Hepatitis A virus (HAV) and hepatitis E virus (HEV) are transmitted via the fecal-oral route and cause self-limiting acute infections. The immune response successfully clears the virus in most healthy individuals within 4–8 weeks, and recovery is complete—no chronic carrier state develops. The critical distinction is that HAV and HEV do not integrate into the host genome or establish persistent reservoirs; once cleared, they're gone. In contrast, hepatitis B virus (HBV) establishes a nuclear reservoir called covalently closed circular DNA (cccDNA) that persists in hepatocytes even when serum viral DNA is suppressed—this is why HBV is so difficult to cure. Hepatitis C virus (HCV), an RNA virus, evades immune detection through rapid mutation (quasispecies diversity) and interferon resistance mechanisms, allowing it to persist chronically in approximately 75–85% of acutely infected individuals.
Hepatitis D virus (HDV) is a defective satellite virus that can only replicate in the presence of HBV—it requires the HBsAg coat protein to assemble infectious particles. This creates two clinical scenarios: co-infection (acquiring both simultaneously, usually self-limiting) versus superinfection (HDV infecting someone already chronically infected with HBV, which dramatically accelerates liver disease progression). This biological dependency is one of the more elegant examples in infectious disease of how viral evolution can produce an organism entirely dependent on another pathogen.
The long-term consequence of chronic HBV or HCV infection is the relentless cycle that builds toward your next topics. Persistent necroinflammation means repeated rounds of hepatocyte death and regeneration, and chronic inflammatory cytokines activate hepatic stellate cells—the liver's resident fibroblasts—to deposit collagen. Fibrosis accumulates progressively, eventually distorting the liver's architecture into the nodular, poorly vascularized state called cirrhosis. Cirrhosis impairs virtually every liver function (protein synthesis, detoxification, bile production) and creates portal hypertension. Superimposed genomic instability from chronic inflammation and regenerative pressure drives the eventual transformation to hepatocellular carcinoma in a subset of patients—a direct application of the multistep carcinogenesis model to a specific viral disease context.
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