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Understanding hepatitis D

What is hepatitis D?

Hepatitis D is a viral disease of the liver. It can take an acute or chronic course. 

The liver is an important organ of the human body and accounts for about 2% of the total weight of an adult.1 It is the central metabolic organ in the body and has many functions, such as:

- Energy storage

- Detoxification station

- Reconstruction station for nutrients

- Control station for sugar and hormone levels in the blood

- Production station for blood components and bile

- Guard station for the immune defense

For this reason, it is important to keep the liver healthy and support the liver in its tasks in the event of illness. 

Hepatitis D only occurs in conjunction with hepatitis B

It is important to know that you can only become infected with the hepatitis D virus (HDV) in the presence of the hepatitis B virus (HBV). Here, a distinction is made between two ways of infection: 

- Simultaneous infection: infection with HBV and HDV occurs simultaneously.

- Superinfection: infection with HBV occurs first, followed by infection with HDV at a later stage2

The HDV or delta virus is an incomplete ribonucleic acid virus (RNA virus), i.e. it requires the presence of another virus (in this case the hepatitis B virus, HBV) in order to be able to form an envelope from its building blocks. This is the only way the virus can infect new liver cells. HDV seems to reproduce exclusively in the liver. Because of its dependence on HBV, HDV can only be transmitted in the presence of an infection with HBV. Either infection with HBV and HDV occurs simultaneously (simultaneous infection), or the person is already chronically ill with hepatitis B (liver inflammation) at the time of HDV infection (superinfection)2. The exact interaction between these two viruses (HDV, HBV) is not yet fully understood.3

According to current research, approximately 12 million people worldwide are infected with HDV.4 This represents 5% of HBV infected people worldwide. HDV infection can lead to acute or chronic (lasting several months and years) hepatitis D (liver inflammation). Chronic infection with HBV/HDV is considered the most serious form of chronic hepatitis of viral origin in humans. It is characterised by a more rapid progression, an increased likelihood of liver cirrhosis (chronic liver disease equivalent to advanced irreversible fibrosis that severely impairs liver function) and a tripled risk of primary liver cancer compared to single HBV infection.3

HDV prevalence in HBsAg-positive individuals relative to the total population (after Stockdale et al, 2020).4

Worldwide prevalence

According to the World Health Organisation (WHO), HDV infection is particularly prevalent in the following regions: Africa (Central and West Africa), Asia (Central and North Asia and Vietnam, Mongolia, Pakistan, Japan, Taiwan, China), Pacific Islands (Kiribati, Nauru), Middle East (all countries), Eastern Europe (Eastern Mediterranean, Turkey), South America (Amazon Basin) and Greenland. However, global estimates and geographic information are incomplete because many countries do not test for HDV.5

References

  1. Kalra A, Tuma F. [Updated 2018 Dec 18]. Physiology, Liver. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan.
  2. Farci P1, Niro GA. Clinical features of hepatitis D. Semin Liver Dis. 2012 Aug;32(3):228-36.
  3. D Koh, Christopher et al. Pathogenesis of and New Therapies for Hepatitis. Gastroenterology, Volume 156, Issue 2, 461 – 476.e1
  4. Stockdale AJ, Kreuels B, Henrion MYR, Giorgi E, Kyomuhangi I, de Martel C, Hutin Y, Geretti AM. The global prevalence of hepatitis D virus infection: Systematic review and meta-analysis. J Hepatol. 2020 Sep;73(3):523-532
  5. Website der WHO Stand 09/03/2020, verfügbar online unter: https://www.who.int/news-room/fact-sheets/detail/hepatitis-d