UniProt release 13.1

A small but deadly pathogen: Hepatitis B virus

The Hepatitis B virus (HBV) causes transient and chronic infections of the liver and constitutes a major cause of human disease. It is estimated that more than 5% of the global population carries the virus, and deaths from liver cancer caused by HBV probably exceed one million per year (see WHO factsheet). An effective vaccine has been available for nearly 20 years, but its high cost still hampers disease control in the developing world.

This killer virus has a surprisingly small genome, about 3.2 kb, which nevertheless encodes for 5 proteins through overlapping open reading frames. It replicates by reverse-transcribing genomic RNA to partial dsDNA through a unique mechanism, and thus belongs to a particular family: the hepadnaviridae.

The virus specifically infects hepatocytes, and most symptoms in an acute infection result from the killing of infected cells by the host immune system. In a few cases, the virus manages to down-regulate the host immunity and establishes a chronic infection. A viral protein secreted in blood is suspected to be involved in chronicity: the HbeAg protein may specifically deplete T-helper lymphocytes, thereby suppressing the ability to mount a strong cytotoxic response against infected hepatocytes.

Our current knowledge of the virus is rather poor due to the lack of cell culture systems allowing in vitro viral propagation. Much of what we know is derived from the study of other closely related hepadnaviridae, such as the woodchuck hepatitis virus (WHV) and the ground squirrel hepatitis virus (GSHV).

In the current UniProtKB/Swiss-Prot release, all hepatitis B virus entries have been updated, and 51 strains representative of the 8 genotypes infecting humans have been annotated. Animal hepatitis B viruses entries have also been revisited, notably WHV and GSHV.