Hepatitis B is a viral infection of the liver, which follows a very variable course. The hepatitis B virus (HBV) can cause an acute illness that resolves itself quickly without causing long-term liver damage. However, in about 20% of cases it causes a chronic illness that lasts more than six months, sometimes for life, with symptoms that come and go. In 15-40% of those with chronic infection cirrhosis, liver cancer or liver failure develop, and so the infection may eventually be fatal.
The virus is usually transmitted through contact with infected blood or body fluids. Only a tiny amount of blood is needed to transmit the virus because it's so infectious. The hepatitis B virus may also be present in saliva, vaginal secretions, breast milk and other bodily fluids. Many people contract hepatitis B while on holiday, especially in countries where it is very prevalent, when unprotected sex, experimenting with drugs and accidents needing medical treatment are far more likely.
The incubation period of the hepatitis B virus before symptoms develop is between six weeks and six months. In the acute phase symptoms vary. Roughly one-third of cases have no symptoms - this is called a silent or subclinical infection, or sometimes anicteric infection, meaning there is no jaundice or yellow appearance of the skin and membranes. In another third of cases, the infection causes mild symptoms similar to those of a flu-like illness, with weakness, aches, headache, fever, loss of appetite, diarrhoea, jaundice, nausea and vomiting. In the final third of cases, the acute phase of infection can cause severe illness that last many months. In addition to the flu-like symptoms, there's abdominal pain, diarrhoea and jaundice.
