Hepatitis D, Hepatitis Delta
What causes the disease?

Hepatitis D or delta hepatitis is caused by the hepatitis delta virus (HDV), a defective RNA virus. HDV requires the help of a hepadnavirus like hepatitis B virus (HBV) for its own replication.

How is HDV spread?

HDV is transmitted percutaneously or sexually through contact with infected blood or blood products.

Blood is potentially infectious during all phases of active hepatitis D infection. Peak infectivity probably occurs just before the onset of acute disease.

Who is at risk for infection?

Chronic HBV carriers are at risk for infection with HDV.

Individuals who are not infected with HBV, and have not been immunized against HBV, are at risk of infection with HBV with simultaneous or subsequent infection with HDV.

Since HDV absolutely requires the support of a hepadnavirus for its own replication, inoculation with HDV in the absence of HBV will not cause hepatitis D. Alone, the viral genome indeed replicates in a helper-independent manner, but virus particles are not released.

Where is HDV a problem globally?

The hepatitis delta virus is present worldwide and in all age groups.14, 21

Its distribution parallels that of HBV infection, although with different prevalence rates (highest in parts of Russia, Romania, Southern Italy and the Mediterranean countries, Africa and South America). In some HBV-prevalent countries such as China, HDV infection is disproportionately low.14

The natural reservoir is man, but HDV can be experimentally transmitted to chimpanzees and woodchucks that are infected with HBV and woodchuck hepatitis virus, respectively.19, 21, 24

When is a HDV infection life-threatening?

HDV infection of chronically infected HBV-carriers may lead to fulminant acute hepatitis or severe chronic active hepatitis, often progressing to cirrhosis.

Chronic hepatitis D may also lead to the development of hepatocellular carcinoma.11

Why is there no treatment for the disease?

Hepatitis D is a viral disease, and as such, antibiotics are of no value in the treatment of the infection.

There is no hyperimmune D globulin available for pre- or postexposure prophylaxis.

Disease conditions may occasionally improve with administration of a-interferon.15, 21, 25

Since no effective antiviral therapy is currently available for treatment of type D hepatitis, liver transplantation may be considered for cases of fulminant acute and end-stage chronic hepatitis D.

The hepatitis Delta virus

The genome of HDV is unrelated to the genomes of hepadnaviruses, of which hepatitis B virus (HBV) is a member. HDV is therefore not a defective-interfering particle of HBV, and should be considered as a satellite virus, a natural subviral satellite of HBV.10, 11, 14, 25

Important parallels can be drawn between HDV and certain subviral agents of plants, especially the viroids, with respect to genome structure and replication mechanisms. Because of the many differences however, HDV has been classified into the separate genus Deltavirus.13, 18, 25

The genome of HDV was cloned and sequenced in 1986.27 HDV is a replication defective, helper (HBV) dependent ssRNA virus that requires the surface antigen of HBV (HBsAg) for the encapsidation of its own genome. The envelope proteins on the outer surface of HDV are entirely provided by HBV.16, 18, 25

The outer envelope of HDV particles actually contains lipid and all three forms (S, M, and L) of HBV surface antigen (HBsAg), but predominantly the major form of HBsAg with very few middle (pre S1) and large (pre S2) proteins. This proportion (95:5:1 of S:M:L) is different from that found in HBV particles.13, 14, 25

There is no evidence that the HBV-derived envelope proteins are additionally modified when they become the envelope of HDV.21

The internal, nucleocapsid structure of HDV is composed of the viral single stranded RNA genome and about 60 copies of delta antigen, the only HDV-encoded protein, in its large and small forms.13, 25

Synthesis of HDV results in temporary suppression of synthesis of HBV components.13

HDV does not infect established tissue culture cell lines. Complete viral replication cycles in vitro are limited to primary hepatocytes, generally of woodchucks or chimpanzees, that are coinfected with a hepadnavirus or cotransfected with hepadnavirus cDNA. When experimental conditions meet these requirements, infectious HDV particles are produced.13, 14, 21

In nature, HDV has only been found in humans infected with HBV. Experimentally, it can be transmitted to chimpanzees and woodchucks in the presence of HBV or woodchuck hepatitis virus (WHV), respectively.13, 18, 19, 21, 24, 25

Morphology and physicochemical properties

HDV virions are 36 - 43 nm, roughly spherical, enveloped particles with no distinct nucleocapsid structure. They do not have distinct spikes on their outer surface and are possibly icosahedral.13, 14, 25

When the virus particle is disrupted with nonionic detergents, an internal nucleocapsid is released and HDAg becomes detectable.13, 25

The 19 nm nucleocapsid contains about 60 copies of HDAg in its two forms (24 and 27 kDa) and HDV genomic RNA.25

The buoyant density of HDV particles is 1.25 g/cm3 in CsCl gradients.13, 14, 18

Genome and proteins

The HDV genome is a single, negative stranded, circular RNA molecule nearly 1.7 kb in length containing about 60% C+G.13, 14, 18, 25

HDV RNA is the only animal virus known to have a circular RNA genome.13

A high degree of intramolecular complementarity allows about 70% of the nucleotides to be basepaired to each other to form an unbranched, double-stranded, stable, rod-shaped structure.10, 13, 14, 18

So far, about 14 different HDV isolates from different parts of the world have been sequenced, and all range from 1670 to 1685 nucleotides in length. Based on sequence similarities, HDV isolates can be classified into three genotypes.13

Genotype I is the most predominant one in most areas of the world, and is associated with a broad spectrum of chronic HDV disease. Originally found in a Japanese isolate, genotype II has been found recently to predominate in Taiwan. Disease associated with genotype II might be less severe than genotype I. Genotype III is associated with outbreaks in Venezuela and Peru. It is responsible for more severe disease in the northern South American regions.5, 10, 11, 13

The genome contains several sense- and antisense open reading frames (ORFs), only one of which is functional and conserved. The RNA genome is replicated through an RNA intermediate, the antigenome.13, 14, 18

The genomic RNA and its complement, the antigenome, can function as ribozymes to carry out self-cleavage and self-ligation reactions.13, 18, 25

A third RNA present in the infected cell, also complementary to the genome, but 800 b long and polyadenylated, is the mRNA for the synthesis of the delta antigen (HDAg).14, 18, 25

The one and only protein expressed by HDV, the hepatitis delta antigen HDAg, is not exposed on the virion outer surface, but is present in the internal nucleocapsid.13, 14, 18

The protein is seen as two species, of 24kD and 27kD. The two species are identical, but the 27kD protein has a 19 aa longer C-terminus. The short form (195 amino acids, HDAg-S), synthesized first, is required for RNA replication; the long form (214 amino acids, HDAg-L), becoming detectable after prolonged replication, suppresses viral RNA replication and is required for packaging of the HDV genome by HBsAg.13, 14, 18, 21, 23

The relative ratios of these two species vary from patient to patient. Two separate ORFs on different RNAs encode HDAg-S and HDAg-L. A single nucleotide at the termination codon for HDAg-S is altered by a specific posttranscriptional RNA editing event in some RNAs, so that the ORF extends for 19 additional amino acids.13

HDAg is a non-glycosylated phosphoprotein.13, 21, 25 It has an RNA-binding activity and appears to bind specifically to HDV RNA in the virus particle.28 In infected cells, HDAg is localized in the nuclei.13, 14, 25

Functional domains present in HDAg include the nuclear localization signal located within the N-terminal one-third of the protein, the RNA-binding motif present in the middle one-third of the protein and a third domain, consisting of the C-terminal 19 amino acids, possibly involved in interactions with the HBsAg during virion assembly, and in the inhibition of HDV RNA assembly.13, 14, 25

The other protein present in HDV particles is HBsAg. This protein is derived from the coinfection with HBV and is essential for HDV virion assembly and virus transmission.

Antigenicity

The intact virus particle is reactive with anti-HBsAg antibody, but not with anti-HDAg antibody.

Despite the sequence heterogeneity observed in HDV isolates from different geographical regions, there appear to be no serological differences among these isolates. 14

All HDV are antigenically related, and antibodies to HDAg do not neutralize HDV.21

Surface epitopes unique to HDV have not been detected.

Under experimental conditions, HDV can use different hepadnaviruses as helpers. In each case, the envelope of HDV has both the physical and antigenic characteristic of the helper virus.

Stability

Because of its double-strandedness, the HDV RNA is relatively stable.

The hepatitis delta virus survives dry heat at 60°C for 30h.14

The disease

An HDV infection absolutely requires an associated HBV infection. The outcome of disease largely depends on whether the two viruses infect simultaneously (coinfection), or whether the newly HDV-infected person is a chronically infected HBV carrier (superinfection).

Coinfection of HBV and HDV (simultaneous infection with the two viruses) results in both acute type B and acute type D hepatitis. The incubation period depends on the HBV titre of the infecting inoculum. Depending on the relative titres of HBV and HDV, a single bout or two bouts of hepatitis may be seen. Coinfections of HBV and HDV are usually acute, self-limited infections. The chronic form of hepatitis D is seen in less than 5% of HBV - HDV coinfected patient.10, 21

Acute hepatitis D occurs after an incubation period of 3 - 7 weeks, and a preicteric phase begins with symptoms of fatigue, lethargy, anorexia and nausea, lasting usually 3 to 7 days. During this phase, ALT and AST activities become abnormal. The appearance of jaundice is typical at the onset of the icteric phase. Fatigue and nausea persist, clay-colored stools and dark urine appear, and serum bilirubin levels become abnormal. In patients with acute, self-limiting infection, convalescence begins with the disappearance of clinical symptoms. Fatigue may persist for longer periods of time.14, 21

Superinfection of HBV and HDV (HDV infection of a chronically infected HBV carrier) causes a generally severe acute hepatitis with short incubation time that leads to chronic type D hepatitis in up to 80% of cases. Superinfection is associated with fulminant acute hepatitis and severe chronic active hepatitis, often progressive to cirrhosis.14, 21

During the acute phase of HDV infection, synthesis of both HBsAg and HBV DNA are inhibited until the HDV infection is cleared.14

Fulminant viral hepatitis is rare, but still about 10 times more common in hepatitis D than in other types of viral hepatitis. It is characterized by hepatic encephalopathy showing changes in personality, disturbances in sleep, confusion and difficulty concentrating, abnormal behavior, somnolence and coma. The mortality rate of fulminant hepatitis D reaches 80%. Liver transplantation is indicated.14, 21

Chronic viral hepatitis D is usually initiated by a clinically apparent acute infection. Symptoms are less severe than in acute hepatitis, and while serum ALT and AST levels are elevated, bilirubin and albumin levels and prothrombin time may be normal. In chronic hepatitis D, the HBV markers are usually suppressed.13, 14, 21

Progression to cirrhosis usually takes 5 - 10 yrs, but it can appear 2 years after onset of infection. About 60 to 70% of patients with chronic hepatitis D develop cirrhosis. A high proportion of these patients die of hepatic failure.21

Hepatocellular carcinoma (HCC) occurs in chronically infected HDV patients with advanced liver disease with the same frequency as in patients with ordinary hepatitis B. HCC may actually be more a secondary effect of the associated cirrhosis than a direct carcinogenic effect of the virus.

Taken together, three phases of chronic hepatitis D have been proposed: a) an early active phase with active HDV replication and suppression of HBV, b) a second moderately active one with decreasing HDV and reactivating HBV, c) a third late one with development of cirrhosis and hepatocellular carcinoma caused by replication of either virus or with remission resulting from marked reduction of both viruses.10

The mortality rate for HDV infections lies between 2% and 20%, values that are ten times higher than for hepatitis B.21

Diagnosis

Hepatitis D should be considered in any individual who is HBsAg positive or has evidence of recent HBV infection.21

The diagnosis of acute hepatitis D is made after evaluation of serologic tests for the virus. Total anti-HDV are detected by commercially available radioimmunoassay (RIA) or enzyme immunoassay (EIA) kits.10, 21

The method of choice for the diagnosis of ongoing HDV infection should be RT-PCR, which can detect 10 to 100 copies of the HDV genome in infected serum.10, 11, 18, 21

- acute HBV-HDV coinfection:


appearence of HBsAg, HBeAg and HBV DNA in serum during incubation
appearence of anti-HBc at onset of clinical disease
appearence of IgM anti-HD, HDV RNA, HDAg in serum
anti-HDV antibodies develop late in acute phase and usually decline after infection to subdetectable levels
if HDAg is detectable early during infection, it disappears as anti-HDV appears
all markers of viral replication disappear in early convalescence, and both IgM and IgG anti-HD disappear within months to years after recovery
- HBV-HDV superinfection:


usually results in persistent HDV infection
HDV viremia appears in serum during preacute phase
high titres of IgM and IgG anti-HDV are detectable in acute phase, persisting indefinitely
titre of HBsAg declines when HDAg appears in serum
progression to chronicity is associated with persisting high levels of IgM anti-HD and IgG anti-HD
HDAg and HDV RNA remain detectable in serum and liver
viremia is associated with active liver disease
Each of the markers of HDV infection, including IgM and IgG antibodies, disappears within months after recovery. In contrast, in chronic hepatitis D, HDV RNA, HDAg, and IgM and IgG anti-HD antibodies persist.14, 18

Host immune response

Both humoral and cellular immunity are induced in patients infected with HDV.14, 21

These immune responses may provide protection from HDV re-infection, or simply modulate clinical symptoms. However, second cases of hepatitis D have not been reported.14, 21

Anti-HD antibodies do not always persist after acute infection is cleared. The serological evidence of past HDV infection is therefore not easy to demonstrate.14

Prevalence

Areas of high prevalence include the Mediterranean Basin, the Middle East, Central Asia, West Africa, the Amazon Basin of South America and certain South Pacific islands.13, 14, 21

Severe, often fatal, acute and chronic type D hepatitis occurs among indigenous people of Venezuela, Colombia, Brazil, and Peru, all regions with high chronic HDV infection rates.21

Hepatitis D is less common in Eastern Asia, but is present in Taiwan, China and India.21

Pathogenesis

Infection with both HBV and HDV is associated with more severe liver injury than HBV infection alone.13

Pathologic changes in hepatitis D are limited to the liver, the only organ in which HDV has been shown to replicate. The histologic changes consist of hepatocellular necrosis and inflammation.21

HDV genome replication is not acutely cytopathic, and both humoral and cellular immune mechanisms may be involved in the pathology of hepatitis D. More experimental data are needed to unravel the underlying mechanisms of HDV-induced disease.10, 14, 21, 25

HBV is an essential cofactor in the evolution of hepatocellular damage.7, 10

Transmission

Transmission is similar to that of HBV:


bloodborne and sexual
percutaneous (injecting drug use, haemophiliacs)
permucosal (sexual)
rare perinatal
Superinfections increase the chance of HDV spread, and at the peak of an acute infection, the amount of HDV in the serum can exceed 1012 RNA-containing particles per ml.25

During an HDV superinfection, the titre of HDV reaches a peak between 2 and 5 weeks postinoculation, after which it declines in 1 to 2 weeks.25

The probability of being productively coinfected, with the coinfection resulting in clinical disease, depends on both the relative and absolute amounts of the two inoculated viruses.25

The main route of transmission is infected blood and blood products.

Risk groups

Here is a list of groups of people who are at risk of contracting HDV:21


intravenous drug users using HDV-contaminated injection needles
promiscuous homosexual and heterosexual groups (although HDV infections are less frequent than HBV or HIV infections)
people exposed to unscreened blood or blood products
°haemophiliacs
°persons with clotting factor disorders
° the risk has decreased in recent years due to better control of blood sources

Incidence/Epidemiology

Seroprevalence studies of anti-HD in HBsAg-positive patients has shown a worldwide but not uniform distribution.21

Epidemics of HDV infections have been described in the Amazon Basin, the Mediterranean Basin and Central Africa.

Two epidemiologic patterns of hepatitis D infections exist: in Mediterranean countries infection is endemic among HBV carriers, and the virus is transmitted by close personal contact. In Western Europe and North America, HDV is confined to persons exposed to blood or blood products, like e.g. intravenous drug addicts sharing unsterilized injection needles.

Worldwide, more than 10 million people are infected with HDV.10, 11

Trends

New foci of high HDV prevalence continue to be identified as in the case of the island of Okinawa in Japan, of areas of China, Northern India and Albania.10

There is a decreasing prevalence of both acute and chronic hepatitis D in the Mediterranean area and in many other parts of the world, which has been attributed to a decline in the prevalence of chronic HBsAg carriers in the general population.10

Immune prophylaxis

Immune prophylaxis against HDV is achieved by vaccination against HBV because HDV uses the envelope proteins of HBV. This mode of prevention is possible only for coinfections in HBV susceptible individuals.10, 21

Immunoglobulin (Ig), hepatitis B (HB) specific Ig and HB vaccine do not protect HBV carriers from infection with HDV.

Vaccines

No vaccines exist against HDV; however, vaccination against HBV of patients who are not chronic HBV carriers, provides protection against HDV infection.

Prevention

Since HDV is dependent on HBV for replication, control of HDV infection is achieved by targeting HBV infections. All measures aimed at preventing the transmission of HBV will prevent the transmission of hepatitis D. HBV vaccination is therefore recommended to avoid HBV-HDV coinfection.14

However, there is no effective measure to prevent HDV infection of chronic HBV carriers, and prevention of HBV-HDV superinfection can only be achieved through education to reduce risk behaviors.14, 21

Promising research results indicate that in some woodchucks immunized with recombinant purified HDAg-S complete protection is possible.

Hepatitis B Ig and HB vaccine do not protect HBV carriers from infection by HDV.

Treatment

Currently there is no effective antiviral therapy available for treatment of acute or chronic type D hepatitis.21

For infected patients, massive doses of a-interferon (9 million units three times a week for 12 months or 5 million units daily for up to 12 months) have yielded remissions, but most patients remained positive for HDV RNA despite the improved disease conditions.21

The effect of interferon is considered to be most likely an indirect one, possibly via an effect on the helper hepadnavirus and/or on the immune response to the infections.25

Acyclovir, ribavirin, lamivudine and synthetic analogues of thymosin have proved ineffective.10

Immunosuppressive agents do not have any effect on hepatitis D.14, 21

Liver transplantation has been helpful for treating fulminant acute and end-stage chronic hepatitis.11, 21 In one study, the 5-year survival rate of transplant patients for terminal delta cirrhosis was 88% with reappearance of HBsAg only in 9% under long-term anti-HBs prophylaxis.10

Guidelines for epidemic measures

1.) When two or more cases occur in association with some common exposure, a search for additional cases should be conducted.

2.) Introduction of strict aseptic techniques. If a plasma derivative like antihaemophilic factor, fibrinogen, pooled plasma or thrombin is implicated, the lot should be withdrawn from use.

3.) Tracing of all recipients of the same lot in search for additional cases.

Future considerations

Whether or not immunization with HDAg can confer protection against superinfection or slow the progression of liver disease in the over 350 million HBV carriers who are at risk of contracting type D hepatitis, needs to be determined.21


Acknowledgements

This guide was prepared by Dr Nicoletta Previsani and Dr Daniel Lavanchy of the World Health Organization.

The contribution to this guide of Dr Mario Rizzetto from the Azienda Ospedaliera S. Giovanni Battista di Torino, Turin, Italy, is gratefully acknowledged.

© World Health Organization, 2001

This document is not a formal publication of the World Health Organization (WHO), and all rights are reserved by the Organization. This document may, however, be freely reviewed, abstracted, reproduced or translated, in part or in whole, but not for sale or for use in conjunction with commercial purposes.

The views expressed in documents by named authors are solely the responsibility of those authors. The mention of specific companies or specific manufacturers' products does not imply that they are endorsed or recommended by the World Health Organization in preference to others of a similar nature that are not mentioned.

The designations employed and the presentation of the information in this manual do not imply the expression of any opinion whatsoever on the part of the Secretariat of the World Health Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.





Reference List
Churchill's Illustrated Medical Dictionary, New York, Churchill Livingstone, 1989.
Dulbecco R. Encyclopedia of Human Biology, San Diego, Academic Press, INC., 1991.
Stedman's Medical Dictionary, 26th ed. Baltimore, Williams & Wilkins, 1995.
Dorland's Illustrated Medical Dictionary, 29th ed. Philadelphia, WB Saunders Co., 2000.
Casey JL et al. Molecular biology of HDV: analysis of RNA editing and genotype variations. In: Rizzetto M, Purcell RH, Gerin JL, and Verme G, eds. Viral Hepatitis and Liver Disease, Turin, Edizioni Minerva Medica, 1997, 290-294.
Centers for Disease Control and Prevention. Epidemiology and Prevention of Viral Hepatitis A to E: An Overview. 2000. http://www.cdc.gov/ncidod/diseases/h...eset/index.htm
Davies SE et al. Evidence that hepatitis D virus needs hepatitis B virus to cause hepatocellular damage. American Journal of Clinical Pathology, 1992, 98(6):554-558.
Dingle K et al. Initiation of hepatitis Delta virus genome replication. Journal of Virology, 1998, 72(6):4783-4788.
Glenn JS et al. Identification of a prenylation site in Delta virus large antigen. Science, 1992, 256:1331-1333.
Hadziyannis SJ. Hepatitis delta: an overview. In: Rizzetto M, Purcell RH, Gerin JL, and Verme G, eds. Viral Hepatitis and Liver Disease, Turin, Edizioni Minerva Medica, 1997, 283-289.
Hadziyannis SJ. Review: Hepatitis delta. Journal of Gastroenterology and Hepatology, 1997, 12(4):289-298.
Hwang SB and Lai MMC. Isoprenylation mediates direct protein - protein interactions between hepatitis large Delta antigen and hepatitis B virus surface antigen. Journal of Virology, 1993, 67(12):7659-7662.
Lai MCC. The molecular biology of hepatitis Delta virus. Annual Review of Biochemistry, 1995, 64:259-286.
Lai MMC. Hepatitis Delta virus. In: Webster RG and Granoff A, eds. Encyclopedia of Virology, London, Academic Press Ltd, 1994, 574-580.
Lau DT et al. Resolutions of chronic Delta hepatitis after 12 years of interferon alfa therapy. Gastroenterology, 1999, 117(5):1229-1233.
Makino S et al. Molecular cloning and sequencing of a human hepatitis delta (?) virus RNA. Nature, 1987, 329:343-346.
Modahl LE and Lai MMC. Transcription of hepatitis Delta antigen mRNA continues throughout hepatitis Delta virus (HDV) replication: a new model of HDV RNA transcription and replication. Journal of Virology, 1998, 72(7):5449-5456.
Monjardino JP and Saldanha JA. Delta hepatitis. The disease and the virus. British Medical Bulletin, 1990, 46(2):399-407.
Negro F. Animal models of hepatitis Delta virus infection. Viral Hepatitis Reviews, 1996, 2(3):175-185.
Polson AG, Bass BL, and Casey JL. RNA editing of hepatitis delta virus antigenome by dsRNA-adenosine deaminase. Nature, 1996, 380:454-456.
Purcell RH and Gerin JL. Hepatitis Delta virus. In: Fields BN, Knipe DM, and Howley PM, eds. Fields Virology, 3rd ed. Philadelphia, Lippincott - Raven, 1996, 2819-2829.
Rizzetto M et al. Immunofluorescence detection of a new antigen-antibody system (d/anti-d) associated to hepatitis B virus in liver and serum of HBsAg carriers. Gut, 1977, 18:997-1003.
Ryu W-S, Bayer M, and Taylor J. Assembly of hepatitis Delta virus particles. Journal of Virology, 1992, 66(4):2310-2315.
Sureau C et al. Cloned hepatitis Delta virus cDNA is infectious in the chimpanzee. Journal of Virology, 1989, 63(10):4292-4297.
Taylor JM. Hepatitis Delta virus and its replication. In: Fields BN, Knipe DM, and Howley PM, eds. Fields Virology, 3rd ed. Philadelphia, Lippincott - Raven, 1996, 2809-2818.
Walton J, Barondess JA, and Lock S. The Oxford Medical Companion, Oxford, Oxford University Press, 1994.
Wang K-S et al. Structure, sequence and expression of the hepatitis delta (delta) viral genome. Nature, 1986, 323:508-514.
Zuccola HJ et al. Structural basis of the oligomerization of hepatitis delta antigen. Structure, 1998, 6(7):821-830.

http://hepcvets.com/hepatitis/delta.html