- Hepatitis D virus (HDV) is a ribonucleic acid (RNA) virus that requires hepatitis B virus (HBV) for its replication. HDV infection occurs only simultaneously or as super-infection with HBV.
- The virus is transmitted through contact with the blood or other body fluids of an infected person.
- Vertical transmission from mother to child is rare.
- Approximately 15 million people across the world are chronically coinfected with HDV and HBV 1.
- Currently there is no effective antiviral treatment for hepatitis D.
- Hepatitis D infection can be prevented by hepatitis B immunization.
Hepatitis D is a liver disease in both acute and chronic forms caused by the hepatitis D virus (HDV) that requires HBV for its replication. Hepatitis D infection cannot occur in the absence of hepatitis B virus. The coinfection or super infection of HDV with HBV causes a more severe disease than HBV monoinfection.
A vaccine against hepatitis B is the only method to prevent HDV infection.
It is estimated that globally, 5% of HBsAg positive people are coinfected with HDV and the distribution is worldwide. High-prevalence areas include the Mediterranean, Middle East, Pakistan, Central and Northern Asia, Japan, Taiwan, Greenland and parts of Africa (mainly the horn of Africa and West Africa), the Amazon Basin and certain areas of the Pacific. Prevalence is low in North America and Northern Europe, South Africa, and Eastern Asia.
The routes of HDV transmission are the same as for HBV: percutaneously or sexually through contact with infected blood or blood products. Vertical transmission is possible but rare. Vaccination against HBV prevents HDV coinfection, and hence expansion of childhood HBV immunization programmes has resulted in a decline in hepatitis D incidence worldwide. However, in some settings, the increase of hepatitis D prevalence has been observed in people who inject drugs, or as a result of migration from areas where HDV is endemic.
Acute hepatitis: simultaneous infection with HBV and HDV can lead to a mild-to-severe or even fulminant hepatitis, but recovery is usually complete and development of chronic hepatitis D is rare (less than 5% of acute hepatitis).
Superinfection: HDV can infect a person already chronically infected with HBV. The superinfection of HDV on chronic hepatitis B accelerates progression to a more severe disease in all ages and in 70‒90% of persons. HDV superinfection accelerates progression to cirrhosis almost a decade earlier than HBV monoinfected persons, although HDV suppresses HBV replication. The mechanism in which HDV causes more severe hepatitis and a faster progression of fibrosis than HBV alone remains unclear.
Who is at risk?
Chronic HBV carriers are at risk for infection with HDV.
People who are not immune to HBV (either by natural disease or immunization with the hepatitis B vaccine) are at risk of infection with HBV which puts them at risk of HDV infection.
Screening and diagnosis
HDV infection is diagnosed by high titres of Immunoglobulin G (IgG) and Immunoglobulin M (IgM) anti-HDV, and confirmed by detection of HDV RNA in serum.
However, HDV diagnostics are not widely available and there is no standardization for HDV RNA assays, which are used for monitoring response to antiviral therapy.
There is no specific treatment for acute or chronic HDV infection. Persistent HDV replication is the most important predictor of mortality and the need for antiviral therapy. Pegylated interferon alpha is the only drug effective against HDV; antiviral nucleotide analogues for HBV have no or limited effect on HDV replication. The optimal duration of therapy is not well defined, nor how long patients need to be HDV RNA negative after the end of therapy to achieve a sustained virological response. More than 1 year of therapy may be necessary.
The overall rate of sustained virological response remains low, including in children, and most patients relapse after discontinuation of therapy. Liver transplantation may be considered for cases of fulminant hepatitis and end-stage liver disease. New therapeutic agents and strategies are needed, and novel drugs, such as prenylation inhibitor or HBV entry inhibitors, have shown early promise.
Prevention and control of HDV infection requires prevention of HBV transmission through hepatitis B immunization, blood safety, injection safety, and harm reduction services. Hepatitis B immunization does not provide protection against HDV for those already HBV infected.
WHO does not have specific recommendation on hepatitis D, however prevention of HBV transmission by hepatitis B immunization, safe injection practices, blood safety, and harm reduction services with clean needles and syringes, are effective in preventing HDV transmission.
In May 2016, The World Health Assembly adopted the first “Global Health Sector Strategy on Viral Hepatitis, 2016-2021”. The strategy highlights the critical role of Universal Health Coverage and the targets of the strategy are aligned with those of the Sustainable Development Goals. The strategy has a vision of eliminating viral hepatitis as a public health problem and this is encapsulated in the global targets of reducing new viral hepatitis infections by 90% and reducing deaths due to viral hepatitis by 65% by 2030. Actions to be taken by countries and WHO Secretariat to reach these targets are outlined in the strategy.
To support countries in moving towards achieving the global hepatitis goals under the Sustainable Development Agenda 2030 WHO is working in the following areas:
- raising awareness, promoting partnerships and mobilizing resources;
- formulating evidence-based policy and data for action;
- preventing transmission; and
- scaling up screening, care and treatment services.
WHO also organizes World Hepatitis Day on 28 July every year to increase awareness and understanding of viral hepatitis.