Hepatitis D is a liver infection caused by the hepatitis D virus (HDV). It is also known as delta hepatitis.

HDV is a small virus that can only infect people who are already infected with hepatitis B virus (HBV).

HDV infection occurs when an individual is infected with both HBV and HDV at the same time, or when someone with chronic HBV infection becomes infected with HDV.

HDV is primarily transmitted through exposure to infected blood, such as through injection drug use, blood transfusions, or sexual contact. It can also be transmitted from mother to child during childbirth.

Symptoms of HDV infection can range from mild to severe and may include fever, fatigue, loss of appetite, abdominal pain, and jaundice (yellowing of the skin and whites of the eyes). 

In some cases, HDV infection can lead to serious liver damage, including cirrhosis (scarring of the liver) and liver cancer.

There is no specific treatment for HDV infection, but antiviral medications may be used to slow the progression of the disease and reduce the risk of liver damage. 

HDV infection can be prevented through vaccination against HBV and practicing safe behaviors, such as using sterile injection equipment and practicing safe sex.