Hepatitis D: Liver inflammation due to the hepatitis D virus (HDV), which only causes disease in patients who already have the hepatitis B virus. Transmission is via infected blood, needles, or sexual contact with an infected person. Symptoms are identical to those of hepatitis B. Chronic infection with HDV is currently treated with interferon, although it is not very successful. HDV infection can be prevented by the hepatitis B vaccine, and by avoiding activities that could lead to getting the virus.