Hepatitis B is inflammation of the liver caused by infection with hepatitis B, a virus. People become infected with hepatitis B from exposure to blood, saliva, semen, or vaginal fluid from an infected person. Patients can have no symptoms or become mildly or severely ill over a period of weeks to months. Some patients will clear the virus, while others will not and become chronically infected. Some patients who are chronically infected are candidates to be treated with antiviral medication.