hepatitis B virus
Meaning of hepatitis B virus: A liver virus whose outcome turns less on the virus itself than on the age of the person it first infects.
Definition of hepatitis B virus
Hepatitis B virus is a small DNA virus that infects liver cells and causes inflammation of the liver. It spreads through blood, through sexual contact, and from an infected mother to her baby around the time of birth. Infection may clear on its own or settle into a lifelong state that slowly scars the liver and raises the risk of liver cancer.
Why does age at infection decide the outcome?
An adult who catches the virus usually feels ill for some weeks and then clears it, because a mature immune system recognizes the infected liver cells and destroys them. A newborn infected around birth usually does not clear it, and the infection becomes lifelong in the great majority. The immune system in infancy tolerates the virus rather than attacking it. This is why the infection remains most entrenched in parts of the world where transmission around birth is common, and why prevention concentrates on the first hours of life.
How does it differ from the other hepatitis viruses?
| Virus | Main route | Becomes long term |
|---|---|---|
| Hepatitis A | Contaminated food and water | No |
| Hepatitis B | Blood, sex, birth | Often, depending on age |
| Hepatitis C | Blood | Usually |
| Hepatitis D | Blood, only alongside B | Yes, and more damaging |
| Hepatitis E | Contaminated water | Rarely, in weakened immunity |
The letters group viruses that share a target rather than a family. Hepatitis D is the odd one out: it cannot build its own outer coat and borrows the surface protein of hepatitis B, so it infects only people already carrying B, and the pair damage the liver faster than either alone. Hepatitis from a virus is only one cause of the inflammation the word names.
Why is it so hard to clear once established?
The virus leaves a stable circular copy of its genetic material inside the nucleus of infected liver cells. Antiviral drugs stop new virus being assembled and can hold the infection down for years, but that reservoir persists, and stopping treatment often lets the virus return. It is also unusual among DNA viruses in copying itself through an RNA intermediate, and fragments of its DNA can insert into the cell's own, which is one route by which it drives cancer even without heavy scarring.
Also known as
Used in a sentence
Hepatitis B virus surface antigen was detected on routine screening.
Good to know
A stable copy of the viral genome persists in the nucleus of infected liver cells, so antiviral treatment suppresses hepatitis B rather than eradicating it, and the virus can drive liver cancer without preceding cirrhosis.
Word origin
Where “hepatitis B virus” comes from
Hepatitis joins the Greek hepar, meaning liver, with -itis, denoting inflammation; virus is the Latin word for poison or venom.