HepatitisD Virus: An Update

Stéphanie Pascarella; Francesco Negro


Liver International. 2011;31(1):7-21. 

In This Article

Clinical Features and Diagnosis

Patterns of Hepatitis D Virus Infection

As HBV is essential for HDV virion assembly and release, HDV infection is always associated with HBV infection. Two major patterns of infection can occur: co-infection and superinfection. A third, minor pattern, the so-called helper-independent latent infection, has been reported in the liver transplant setting, and will be briefly discussed below.

Co-infection is a simultaneous infection with both viruses that leads to acute hepatitis B and D. From a clinical point of view, this is indistinguishable from acute hepatitis B,[32] although it may be more severe and two peaks of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) may be observed. Because HBV is essential for HDV, the rate of progression to chronicity is the same as that of acute hepatitis B (<5%).

Superinfection is the HDV infection of an individual chronically infected with HBV. This way of infection causes severe acute hepatitis, which progresses to chronicity in almost all patients (up to 80%).[32] Once chronic HDV infection is established, it usually exacerbates the pre-existing liver disease due to HBV.[33] HBV replication is, however, usually suppressed to low levels during the acute phase of HDV infection. This suppression becomes persistent in case of a chronic hepatitis D establishment[34,35] (Table 1).

Helper-independent latent infection was initially reported to occur after liver transplantation.[36] HBV infection of the grafted liver is usually prevented by administration of hepatitis B immunoglobulins. Hepatocytes may thus be infected with HDV alone. HDAg can be detected in the liver by immunohistochemistry before HBV recurrence, as the helper virus in only necessary for particle formation and not for viral replication.[37] HDV viraemia (as determined by molecular hybridization) is only observed several months later on, when residual HBV evades neutralization, thus allowing for HDV rescue and cell-to-cell spread.[36] This third pattern of infection has been revisited with the advent of more sensitive, reverse transcription (RT)-PCR-based techniques for detecting HDV RNA. Moreover, experiments on chimpanzees first infected with HDV and later challenged with HBV have shown a rescue of HDV when HBV inoculation was performed at day 7 but not at 1 month.[38]

Route of Hepatitis D Virus Transmission

The natural reservoir is man, even though chimpanzees infected with HBV and woodchucks infected with the woodchuck hepatitis virus can be infected by HDV. Infection with HDV is parenterally transmitted. In industrialized countries, high-risk populations include illicit drug users and people exposed to blood or blood products. HDV does not seem to be a typically sexually transmitted disease, as the frequency of infection in sexually promiscuous heterosexual or homosexual groups is lesser than that of HBV or HIV.[39] In Taiwan, however, this route is the predominant way of transmission.[40] In socially and economically disadvantaged populations, many infections occur by inapparent intrafamilial routes of transmission, facilitated by poor hygiene. Perinatal transmission of HDV is rare.

Markers and Diagnosis

Hepatitis D virus induces innate and adaptive immune response in the infected host, which consist of immunoglobulin M (IgM) and IgG production.[41] Therefore, in the serum, the three specific HDV markers are HDV RNA, HDAg and anti-HDV.

Hepatitis D virus RNA can be detected in serum by either molecular hybridization or RT-PCR. Hybridization assays have a detection limit of about 104–106 genomes/ml.[42–44] This technique has been superseded by RT-PCR, which is more sensitive, with a detection limit of 10 genomes/ml.[45–49] In liver samples, HDV RNA can be detected by in situ hybridization. This method is, however, not used in routine as it is very difficult and time-consuming. New automated assays are now being established to render possible the follow-up of viral RNA kinetic in the serum of infected patients during treatment.[50,51]

Serum HDAg can be detected by two different methods, namely the enzyme-linked immunosorbent assay (ELISA)[52] and the radioimmunoassay (RIA). These assays are not available in the US for clinical diagnosis. HDAg can be detected by immunofluorescence or immunohistochemical staining of liver biopsies.

As HDAg, serum anti-HDV IgM and IgG antibodies can be detected by ELISA or RIA.

The diagnosis has of course to indicate whether there is an HDV infection, but it also has to distinguish among the three situations of infection: acute HBV/HDV co-infection, acute HDV superinfection of a chronic HBV carrier or HDV chronic infection.

As HDV is dependent on HBV, assessing the presence of HBsAg is necessary before investigating the other markers in order to establish the diagnosis.

Acute HBV/HVD co-infection is highlighted by the presence of a high titre of IgM anti-HBc, antibodies that disappear in chronic HBV infection. It bears otherwise the same characteristics as acute HDV superinfection. HDAg appears early but also disappears quickly. Repeated testing is necessary so that it does not elude detection.[53] In immunodeficient patients, HDAg lasts longer as these people have a slow and weak immune response.[54] HDV RNA is an early and sensitive marker of HDV replication in acute phase[43] and is present in 90% of the patients. In the setting of superinfection, the amount of HDV in the serum can reach 1012 RNA-containing particles per ml between 2 and 5 weeks post-inoculation, at the peak of acute infection. Anti-HD antibodies appear late but seroconversion allows one to establish diagnosis in the absence of other tests.

In chronic HDV infection, HDAg are complexed with anti-HD that are present at a high titre. HDAg are thus not detectable by ELISA but can be well visualized by immunoblot assay under denaturating conditions.[55] Unfortunately, even though this technique is very sensitive,[56] it is difficult to apply for routine detection, as it is time and labour consuming. The detection of the HDAg in the liver is only possible in about 50% of patients chronically infected for 10 years or more.[49] HDV RNA is usually detectable in the serum. The titre of anti-HD antibodies of the IgG class is very high in chronic patients and may help distinguishing current from past infections. The persistence of anti-HD of the IgM class after the acute phase is characteristic of the progression to chronicity, at variance with other viral hepatitis infections (Table 1 and Fig. 2).

Figure 2.

Serologic pattern of type D hepatitis. Expression level of antigen, DNA or RNA, IgM and IgG for both HDV and HBV and ALT.

To summarize, the first step towards establishing diagnosis is to test for anti-HD antibodies. Diagnosis can then be confirmed by immunohistochemical staining for HDAg in the liver or the detection of serum HDV RNA.

If HDV infection is confirmed, the next step is to evaluate liver grading and staging to determine whether the patient will benefit from a potential treatment.

Natural History of the Disease

Hepatitis D virus induces a usually severe form of hepatitis. However, the range of clinical manifestations is very broad as HDV infection can be associated with asymptomatic cases as well as with cases of fulminant hepatitis.[57,58]

Acute hepatitis occurs after an incubation time of 3–7 weeks. The preicteric phase is characterized by several non-specific symptoms such as fatigue, lethargy, anorexia or nausea and the appearance of biochemical markers, such as elevated serum ALT and AST activities. The icteric phase, which is not always observed, is characterized by elevated levels of serum bilirubin.

Fulminant viral hepatitis, which may occur especially in the setting of superinfection, is more frequent in hepatitis D than in hepatitis B alone.[32] It is characterized by a massive hepatocyte necrosis that leads to liver failure and death in 80% of the patients, unless urgency liver transplantation is carried out.

The course of chronic hepatitis D is often more severe than other types of chronic hepatitis. Clinically, it may be asymptomatic or present with non-specific symptoms. The diagnosis is often fortuitous or may follow the appearance of late complications at the cirrhosis stage. ALT and AST levels are persistently elevated in most patients. Within 5–10 years, as many as 70–80% of chronic hepatitis D patients may develop cirrhosis[59,60] and 15% within 1–2 years.[61] Overall, the relative risk of developing cirrhosis during follow-up in patients co-infected with HBV and HDV seems two-fold compared with patients mono-infected with HBV.[62] Cirrhosis due to HDV may remain stable for many years before progressing to liver failure or developing into hepatocellular carcinoma (HCC). Patients with HDV-associated cirrhosis have a probability of survival of 49 and 40% at 5 and 10 years respectively.[63] The impact of HDV infection on the acceleration of HCC development in HBV-positive patients is controversial. A retrospective study on patients suffering from compensated, HBV-related cirrhosis in Western Europe, where HDV genotype 1 is predominant, has demonstrated a three-fold and two-fold risk increase, respectively, of developing HCC and of death in HDV patients compared with those mono-infected with HBV.[64] A study in Taiwan, where genotype 2 prevails, has highlighted the fact that this specific genotype is less often associated with fulminant hepatitis or unfavourable long-term outcome than genotype 1.[30]

Factors Influencing Liver Disease Progression

Many factors can influence the outcome of chronic hepatitis D. A major one is the modality of infection with HBV (i.e. co-infection vs superinfection). Another one is the HDV genotype.[23,30] Indeed, infection with genotype 3, which is predominant in South America, induces a severe acute hepatitis with a high risk of liver failure.[23,65,66] Another factor potentially involved in influencing disease outcome is the occurrence of specific HDAg species that have been reported in fulminant hepatitis.[67] The HBV genotype is also responsible as it modulates the HDV viral load and correlates with adverse outcome.[68,69] Furthermore, high levels of HBV replication are associated with more severe liver damage also in the context of chronic hepatitis D.[70]