Hepatitis D is a viral infection that affects the liver and is caused by the hepatitis D virus (HDV). It can only occur in individuals who are already infected with hepatitis B (HBV), as HDV requires HBV to replicate. This co-infection can lead to more severe liver disease, including cirrhosis and liver cancer. Transmission of hepatitis D occurs through contact with infected blood, similar to hepatitis B. Symptoms may include fatigue, jaundice, and abdominal pain, but some people may not show any symptoms. Vaccination against hepatitis B can prevent hepatitis D, as it cannot exist without the presence of HBV.