HDV

Hepatitis D, also known as Hepatitis Delta, is a type of viral hepatitis caused by the Hepatitis D virus (HDV). It is unique among the hepatitis viruses because it requires the presence of Hepatitis B virus (HBV) to replicate and propagate. This dependency makes HDV a satellite virus, and its infection is considered one of the most severe forms of chronic viral hepatitis due to its rapid progression towards liver-related complications.

HDV is a small, spherical, enveloped particle with a diameter of approximately 36 nm. The viral envelope contains host phospholipids and three proteins derived from HBV: the large, medium, and small hepatitis B surface antigens. Inside the envelope, the virus contains a ribonucleoprotein (RNP) particle, which includes the HDV genome surrounded by about 200 molecules of hepatitis D antigen (HDAg). The HDV genome is a negative-sense, single-stranded, closed circular RNA, making it the smallest known virus to infect animals .

HDV can be transmitted through broken skin (via injection, tattooing, etc.) or contact with infected blood or blood products. Transmission from mother to child is rare. HDV infection occurs either through simultaneous infection with HBV (co-infection) or superimposed on chronic hepatitis B or hepatitis B carrier state (superinfection). The latter is considered the most serious type of viral hepatitis due to its severity and complications, including a higher likelihood of liver failure and rapid progression to liver cirrhosis and liver cancer .

Globally, HDV affects nearly 5% of people with chronic HBV infection. Certain populations are more likely to have HBV and HDV co-infection, including indigenous populations, recipients of haemodialysis, and people who inject drugs. Geographical hotspots of high HDV prevalence include Mongolia, the Republic of Moldova, and countries in western and central Africa .

The clinical manifestations of HDV infection can range from mild to severe. Symptoms may include fatigue, nausea, vomiting, and jaundice. Chronic HDV infection can lead to severe liver disease, including cirrhosis and hepatocellular carcinoma. The combination of HDV and HBV infection has the highest fatality rate among all hepatitis infections, with an estimated 20% mortality rate .

Vaccination against HBV is the primary method to prevent HDV infection, as HDV cannot propagate without HBV. Despite the availability of HBV vaccines, treatment success rates for HDV infection remain low. Antiviral treatments and pegylated interferon alpha are used to manage HDV infection, but their efficacy is limited. Bulevirtide, a newer medication, has shown promise in treating HDV .