Hepatitis viruses

The hepatitis viruses are five viruses from different families that share a target organ: the liver. Labeled hepatitis A through E, they all cause hepatocyte inflammation and injury, producing symptoms such as jaundice, fatigue, dark urine, and elevated liver enzymes — but they differ sharply in how they spread, whether they persist, and how they're prevented.

Transmission divides them into two groups. Hepatitis A (a picornavirus) and hepatitis E (a hepevirus) spread by the fecal-oral route through contaminated food and water, cause acute self-limited illness, and do not establish chronic infection in healthy hosts — though hepatitis E is notably dangerous in pregnancy. Hepatitis B (a hepadnavirus with a DNA genome), hepatitis C (a flavivirus), and hepatitis D spread parenterally — through blood, sexual contact, and from mother to child.

Chronicity is the other key axis. Hepatitis C becomes chronic in the majority of infections, and chronic B or C infection drives cirrhosis and hepatocellular carcinoma over decades. Hepatitis D is a defective virus that requires the hepatitis B surface antigen to replicate, so it infects only alongside B — either as a coinfection or a superinfection of a chronic B carrier, the latter carrying the worse prognosis. Vaccines exist for hepatitis A and B, and the B vaccine indirectly prevents D.

For the USMLE Step 1, hepatitis viruses are core virology: expect questions on virus families and genomes, transmission routes, chronicity risk, the B-D relationship, and especially hepatitis B serologic markers — interpreting surface antigen, surface antibody, and core antibody patterns to distinguish acute infection, chronic infection, immunity, and vaccination.