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Testing for Hepatitis B Virus

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Clinical Features of Hepatitis B

Most hepatitis B virus (HBV) infections are subclinical, particularly in childhood while in adults only about one third of infections are icteric. Clinically the course of HBV infection is conventionally divided into three phases; i) preicteric, ii) icteric and iii) convalescent.

Following an incubation of 6 to 24 weeks the prodromal preicteric phase commences with lethargy, anorexia, commonly nausea, vomiting and right upper quadrant pain. A minority of patients may develop serum sickness during the prodrome consisting of mild fever, urticaria, polyarthritis which resembles a benign fleeting form of rheumatoid arthritis. After 2 days to 2 weeks of prodrome the icteric phase begins with dark urine (bilirubinuria), pale stools and jaundice. The convalescent phase may be long and drawn out over several weeks with fatigue and malaise.

There are a number of possible outcomes. Less than 1% of icteric cases die of acute fulminant hepatitis. Most patients recover fully with regeneration of liver cells within 2 to 3 months, but a proportion progress to chronic infection. Chronic infection may manifest as:

1. asymptomatic, defined as persistent HBs antigenaemia for at least 6 months.
2. chronic persistent hepatitis.
3. chronic active hepatitis causing progressive liver damage which may eventually lead to cirrhosis and/or primary hepatocellular carcinoma.

A proportion of patients with chronic persistent hepatitis or chronic active hepatitis develop manifestations of immune-complex disease; systemic necrotising vasculitis (polyarteritis nodosa) and membranoproliferative glomerulonephritis being the most common.

The hepatitis B carrier can be divided into high and low replicative phases. In the high replicative phase or productive phase the liver is supporting a large amount of viral replication; HBsAg, HBV DNA and HBeAg are found at high titre in the peripheral blood. In contrast, the low replicative phase or restricted phase is characterised by much lower titres of HBsAg, extremely low HBV DNA and absent HBeAg but the presence of anti-HBe. Some carriers have a poor prognosis developing chronic progressive liver disease while others have a much more benign prognosis.

Laboratory Diagnosis

Routine biochemical tests of liver function usually distinguish viral hepatitis from the many non-viral, for example toxic and obstructive, causes of jaundice. Characteristically serum transaminases (aminotransferases) are elevated markedly (5 to 100 fold) in acute symptomatic viral hepatitis, whether due to hepatitis viruses A,B,C,D or E. Alanine aminotransferase (ALT) and aspartate amintransferase (AST) rise together late in the incubation period and peak about the time jaundice appears; they gradually revert to normal over about two months in uncomplicated cases. Serum bilirubin may rise up to 25-fold, depending on severity, and may of course be close to normal in anicteric cases.

To date no reliable convenient culture system for the detection of HBV has been developed so serology forms the basis of diagnosis and differentiation of the various forms of HBV infection(table1). Six markers, all found in serum, are of particular diagnostic importance: HBsAg, HBV DNA, HBeAg, antibody to HBsAg (anti-HBs), antibody to HBeAg (anti-HBe) and antibody to HBc (anti-HBc). The use of relevant markers is indicated in Table 2.

Acute infections:

This is characterised by the appearance of HBsAg a month or two after infection, rising to a peak shortly before symptoms appear, then gradually disappearing coincidently with the fall in transaminases over the next few months, HBV DNA and HBeAg appear at about the same time as HBsAg but disappear more abruptly when symptoms and enzyme levels peak. The first antibody that is detected is anti-HBc (initially IqM); it usually appears before symptoms develop, rises rapidly to high tire and persist indefinitely. Anti-HBs does not become detectable until HBsAg is cleared. Occasionally there is a window in time when neither HBsAg or anti-HBs are detected and anti-HBc is the only detectable marker. This period is referred to as the core window. (Figure 1 and Table 1).

Chronic Infections:

Characterised by the persistence of HBsAg for over 6 months, but often for years or for life. While HBsAg persists anti-HBs will usually not be detected. Anti-HBc rises to a very high titre and persist for life. This is the HBsAg carrier state. (Figure 2 and Table 1)

Chronic Active Hepatitis:

This is distinguished from the asymptomatic carrier state by the progression of liver damage, as indicated by persisting elevation of transaminases and / or the histologic evidence of liver damage on biopsy. The persistence of HBsAg, HBeAg and HBV DNA implies active viral replication, high infectivity and progressive liver damage. In contrast, the development of anti-HBe, which develops after HBeAg disappears and enzyme levels have declined, indicates a long standing carrier state characteristic of the low replicative phase (Table 1).

Hepatitis D

The delta agent, now known as hepatitis D virus (HDV) is absolutely unique amongst the human viruses as it contains a tiny RNA genome and has an outer coat composed of surface antigen from HBV (HBsAg). The HDV is a defective satellite virus, found only in association with its helper virus HBV.

Thus there are two main types of infection with HDV, coinfection or superinfection of a patient infected with HBV. The most common mode of transmission is parenteral usually in intravenous drug users and the incidence of this infection is very low in Australia.

Coinfection with HDV is defined as simultaneous primary infection of a HBV susceptible person with HDV and HBV. The incubation period varies with inoculum but is usually 6 weeks to 6 months. Clinically most patients have a single episode of hepatitis B and hepatitis D which is usually more severe than hepatitis B alone and a higher incidence of fulminant hepatitis. A small proportion (10 to 20%) have two discrete clinical episodes namely hepatitis B followed closely by hepatitis D. The clinical pattern is dependent upon the relative inoculum of HBV and HDV. The proportion of patients who progress to chronic infection is no higher in HBV and HDV coinfection than in HBV infection alone.

Superinfection of a HBsAg carrier by HDV is more common than coinfection and usually more serious. It is manifest as a second episode of acute severe hepatitis in a HBsAg carrier with a case fatality rate of about 20% from acute fulminant hepatitis. The incubation period for HDV superinfection, usually about 3 weeks, is much shorter than that of HDV coinfection as there are already high levels of HBsAg being produced by the HBV carrier. A small proportion of patients with chronic active hepatitis or cirrhosis are infected with HDV.

Laboratory Diagnosis of Hepatitis D

HDV infection is diagnosed serologically with anti-HD IgM and total anti-HD. Serology is only available in situations where the patient is documented as HBsAg positive with raised transaminases. In simultaneous coinfection anti-HD IgM is demonstrable late in acute infection. The anti-HD IgG is short lived following acute infection and is therefore not a reliable marker of past infection. In contrast, superinfection by HDV of a HBsAg carrier is distinguished from acute coinfection by the absence of anti-HBc IgM as well as the presence of both anti-HD IgM and IgG. There are exceptions to this serological profile making interpretation of the results difficult. 

HBV DNA is not available as a routing diagnostic test. It is only available in very special circumstances after consultation with the Medical Virologist.

Figure 1. Serological events in acute hepatitis B

Figure 2: Serological events in the development of HBV carrier state.

Reference

White D.O and Fenner F. Hepadnaviridae and Deltavirus. In Medical Virology 4th Ed. Academic Press. San Diego. 1994

Written by:         Dr Alison Kesson, Microbiology, HAPS

Last Reviewed:     Sept 2005