Hepatitis A-E Slide Set

HEPATITIS_B

The Australia antigen was discovered by Blumberg et al. in 1965 which was recognized to be associated with hepatitis B. Previously hepatitis B was diagnosed on the basis of infection occurring 60 - 180 days after the injection of human blood or plasma fractions or the use of inadequately sterilized needles. Hepatitis B is the only human representative of a family of DNA viruses (Herpadnaviradae) of which related viruses have been found in woodchucks, Peking ducks and ground squirrels.

Properties

Double stranded DNA virus,the + strand not complete
Replication involves a reverse transcriptase.
Complete Dane particle 42 nm
28 nm electron dense core, containing HBcAg and HBeAg
The coat and the 22 nm free particles contain HBsAg
At least 4 phenotypes of HBsAg are recognized;
adw, adr, ayw and ayr.
The HBcAg is of a single serotype
It has not yet been possible to propogate the virus
in cell culture.
 

Structure of Hepatitis B Virus particle

 

Electron microscopy of hepatitis B virus-positive serum reveals 3 morphologically distinct forms of particles ;-

1. Small 22nm spherical or tubular forms comprise of virus surface proteins which are synthesized in excess of the 42 nm complete virions.

2. Complete 42 nm virion (Dane particle). The HBsAg differs from the HBsAg found in the 22 nm particles in that pre-S1 epitopes are present.

3. The 27 nm nucleocapsid comprises of the DNA genome surrounded by a second protein, the HBcAg. A third antigen, the HBeAg is found in the soluble forms in virus-positive sera and is related to the core antigen.
    

The genome comprises of circular DNA and the positive strand is incomplete (50 - 80%). The genomes of a variety of isolates of hepatitis B ave been sequenced. Although there is some variation in sequence (up to 12%), the genetic organization is conserved. There are 4 open reading frames derived from the same strand (the incomplete + strand). The first reading frame codes for the proteins making up HBsAg, the second for HBcAg, the third for the viral polymerase, the function of the fourth is unknown.

The major protein of HBsAg is 226 a.m.u. long and is found in both glycosylated and non-glycosylated form (gp 27 and p24). The gene region it is translated from is called S. However larger proteins can be translated from 2 initiation codons that are situated further upstream in the pre-S region. The pre-S2 proteins (gp33 and gp36) appear to be minor components of both 42 nm virion and 22 nm subunit particles. The largest pre-S1 proteins (p39 and gp42) appear to be found only in the complete 42 nm virions. A domain on the pre-S1 region may be responsible for the attachment of the virion to the hepatocyte. The major HBsAg protein also carries a pair of mutually exclusive subdeterminants, d or y and w or r. 4 principle phenotypes of HBsAg are recognized ; adw, adr, ayw and more rarely ayr. These phenotypes show differing geographical distribution e.g.. ayw predominates in N. Europe, N. America and Australia ; adr in China and Japan.

The core protein is the major component of the nucleocapsid. HBeAg may be generated from the core protein by proteolytic cleavage. The P reading frame codes for the viral polymerase. The function of the product of the X reading frame is uncertain but appears to act as a transcriptional activator which may enhance the expression of other proteins. . Variants of HBV have been described in Taiwan, France, Italy and Senegal which shares a few epitopes with the envelope of classical HBV but no cross reactivity with the core or e antigen. There is no anti-HBc response and no cross protection from the anti-HBs Ab.

Replication ;- The replicative process of the hepadnaviruses is unique among animal DNA viruses in that reverse transcription is involved. After absorption, the virus is uncoated and the single-stranded region of the genome is repaired by the viral polymerase. Viral RNAs are transcribed some of which act as mRNAs, others act as templates for the synthesis the progeny genomes where the process of reverse transcription is involved.
 

Epidemiology

Blood and blood products are the main routes through which the virus is transmitted. Only a very small amount of blood is needed for transmission (down to 0.00004 ml intradermally). Any technique that allows the transfer of blood or serum from one individual to another is potentially likely to transmit HBV. HBV infection is especially common amongst IV drug abusers. Before the advent of screening, many cases occurred following blood transfusion. It is also particularly common amongst homosexuals where the practice of anal intercourse is particularly traumatic and frequently results in bleeding. Cases have been reported following acupuncture, tattooing and ear piercing.

HBV is a known occupational hazard. The risk to health workers following accidental inoculation is 6 - 20%. Health personnel in renal dialysis units are particularly vulnerable. It is striking that infected professionals often develop severe disease whereas their immunocompromised do not, suggesting that an immunopathological mechanism may be involved in the pathogenesis of the disease. Many infected health workers on the haemodialysis units do not recall any accidental inoculation.

It has become clear that HBV is not spread exclusively by blood and blood products. Under certain circumstances, the virus is infective by mouth. It is endemic in closed institutions such as homes for the mentally handicapped and prisons. The virus is also found in semen, vaginal discharges, breast milk and serous exudates such as the CSF and these have been implicated as possible vehicles of transmission. The presence of HBV antigens has been reported in urine, faeces, bile, sweat and tears but has not been confirmed. There have been cases of family outbreaks of hepatitis B where no known exchange of blood has occurred. The entrance of the virus through the membranes of the eye or mouth must be a possible route of transmission. All biological fluids from a HBV infected individual must be treated as potentially infectious. Although HBsAg has been detected in mosquitoes and bed bugs, there is no convincing evidence for replication of the virus in these insects. The role of arthropod vectors in uncertain although mechanical transmission of infection must be a possibility.

Clustering of HBV infection also occurs within family groups, but does not appear to be related to genetic factors and does not reflect maternal or venereal transmission. HBV does not normally infect the fetus but the baby is at risk of infection during the birth process. The perinatal transmission of HBV is an important factor in maintaining the high level of carriers and thus the prevalence of HBV infection in some regions, notably China and S.E Asia. The risk of transmission to the fetus may reach 50 - 60%, though it varies from country to country and appears to be related to ethnic groups. The risk is greatest if the mother has a history of transmission of infection to previous children or has a high titre of HBsAg or e antigen. There is also a substantial risk of perinatal infection if the mother had acute hepatitis B in the second or third trimester of pregnancy or within 2 months of delivery. Although HBV can infect the fetus in utero, this appears to be rare and is generally associated with antepartum haemorrhage and tears in the placenta. The mechanism of perinatal transmission is uncertain. It probably occurs during or shortly after birth as a result of a leak of maternal blood into the baby's circulation or of its ingestion or inadvertent inoculation. Most children infected during the perinatal period become persistent carriers. 70 - 90% of infants born to e +ve mothers become carriers.

Hepatitis B infection is found worldwide but the prevalence varies enormously between different countries. It is estimated that one-half of the world population has experienced infection and there are 350 million chronically infected individuals. Hepatitis B is responsible for 1.5 million deaths per year. Around 40% of chronically infected individuals will die as a result of their infection. The high carrier rate and the high rate of perinatal infection appears to be the mechanism for maintaining the high prevalence rate in some countries. In high prevalence areas, infection in infancy is very common, particularly acquired from the carrier mothers at birth. The earlier in life the infection, the more likely is persistent carriage to be the outcome. The result is that the carrier rate in the adult population is 10 - 20% and almost all the remainder of the population is immune. In areas of intermediate prevalence, infection is also common in childhood but is usually horizontal between children. This may be due to the fact African HBV carrier mothers are less likely to be e +ve than their Oriental counterparts and thus less likely to transfer HBV perinatally. The carrier rate in adults is 2 - 10% and a quarter to half the population is immune. In low prevalence areas, infection in childhood is rare, the carrier rate is low, 0.1 - 0.5% with a low prevalence of natural immunity in the general population being in order of 2 - 6%. The UK having one of the lowest rates.

E.Europe

                        N and W.Europe     Mediterranean     Parts of China

                        N.America USSR     SW.Asia           S.E.Asia

                        Australia          S.America         Tropical Africa

HBsAg                    0.2 - 0.5%         2 - 7%           8 - 20%

Anti-HBs                 4 - 6%             20 - 55%         70 - 95%

Neonatal infection       Rare             Frequent         Very Frequent

Childhood infection     Infrequent        Frequent         Very Frequent

The Carrier State

The carrier state is defined as persistence of the HBsAg in the circulation for more than 6 months. The carrier state may be lifelong and may be associated with mild liver damage varying from minor changes in liver function to chronic active hepatitis and cirrhosis and hepatocellular carcinoma. The carrier state is more likely to occur if the infection occurred earlier in childhood rather than adults. It is more frequent in males and more likely to occur in those with acquired or natural immune deficiencies. Approximately half the carriers are e antigen positive. A carrier state is established in 5 - 10% of infected adults. The e antigen is also more likely to be positive in younger carriers.
 

Pathogenesis

Infected hepatocytes are characteristically enlarged and their cytoplasm has a ground glass appearance. HBsAg is found associated with the endoplasmic reticulum, core particles containing HBcAg are present in the cell nuclei. Due to large antigenic load present in hepatocytes and in the serum, together with the knowledge is more likely to be asymptomatic or mild in the immunocompromised, it has been postulated that liver injury may result from immune mechanism. Necrosis of hepatocytes results in scattered focal inflammatory response with macrophage and lymphocyte infiltrations together with portal inflammation and endophlebitis of the central veins. In more severe cases, lines of necrosis extends from the portal tracts to the central veins and this often precedes chronic hepatitis and cirrhosis.

Those who become asymptomatic carriers may either have normal liver histology or may show chronic liver inflammation that is recognized as chronic persistent hepatitis. This normally resolves within months or years of acute infection. Some may develop chronic periportal hepatitis which correlates clinically with chronic active hepatitis and continuing patchy necrosis with fibrosis is likely to lead to the major disruption in liver architecture characteristic of cirrhosis. It takes around 4 to 5 years for cirrhosis to develop. Some carriers may go on to develop hepatocellular carcinoma.
 
 

Clinical Features

The incubation period for hepatitis B is 6 weeks to 6 months ie. 40 - 180 days (ave. 90 days or 3 months). As with hepatitis A the clinical picture is very variable, although the disease is on the whole more severe than hepatitis A. Asymptomatic and minor non-specific infections are common. The onset is insidious, with a non-specific prodrome consisting of fever, fatigue, nausea, diarrhoea, anorexia, chills, discomfort or pain in the right hypochondrium. The prodrome may be present for 1 - 3 weeks before the jaundice becomes apparent. Arthritis and urticaria are common and may sometimes precede the jaundice and these are thought to be due to circulating immune complexes. The onset of the jaundice is insidious and is accompanied by the darkening of urine and pale stools. In children, the onset of symptoms is more abrupt and the icteric phase shorter. GI disturbances predominate with vomiting, abdominal pain and ketoacidosis being usual. Although urticaria and arthritis are uncommon in children, other immune complex phenomena, particularly glomerulonephritis and papular acrodermatitis are relatively common. Recovery normally takes 6 to 12 weeks after the onset of illness. About 0.1% of patients presenting with acute hepatitis B develop fulminant hepatitis with death from liver failure. The mortality of acute HBV infection increases with age and also with the presence of other disorders.
 

The Immune Response and the Carrier State

Following HBV infection,the first marker to appear is HBsAg, which is evident 2 to 8 weeks before the appearance of the jaundice and biochemical evidence of liver damage. Next to appear are the markers of the virion, such as virus-specific DNA polymerase activity, the viral DNA and the soluble antigen, HBeAg. Although HBcAg is present, it is not detectable in the serum due to the early appearance of anti-HBc. Anti-HBc is found 2 - 4 weeks after the appearance of the surface antigen, at around the same time as the development of the signs and symptoms. In acute infections, clearance of the virus is marked by the disappearance of HBeAg and the appearance of anti-HBe. Later during convalescence, HBsAg also disappears with the appearance of anti-HBs. CMI to HBsAg appears near the end of the acute phase of hepatitis and appears to be mainly responsible for the disappearance of HBsAg. In contrast, anti-HBs does not appear until months after the termination of the clinical illness. It is noteworthy that in chronic HBsAg carriers specific CMI is generally decreased and circulating anti-HBs is not demonstrable. However, on electron microscopic examination of the patients' sera reveal HBsAg - anti-HBs immune complexes. An increase in anti-HBs is clearly correlated with immunity. In the case of approx. 10% of infected adults and a much larger percentage of perinatally infected children, the immune system fails to clear the infection and a carrier state develops (The carrier state is defined as the persistence of HBsAg in excess for more than 6 months). The carrier state may be divided into 2 phases ;-

(1) Virus replication continues and the patient is positive for HBeAg and the markers of the virion (viral DNA and DNA polymerase). Although HBeAg correlates with the presence of the virus and thus infectivity, in some cases, virus replication declines to very low levels and seroconversion to anti-HBe may occur. Therefore detection of viral DNA and DNA polymerase (by PCR or hybridization or the endogenous polymerase reaction) is a more reliable indicator of viral replication and infectivity. (It is not uncommon for HBV DNA to be detected in e -ve carriers nor is it uncommon for HBV DNA to be undetectable in e +ve carriers.) During this phase of chronicity, replicative forms of HBV DNA may be detected in the liver. Levels of virus replication may decline until this is eliminated with the development of anti-HBe. Rarely there will also be seroconversion to anti-HBs.

(2) In this second phase, HBsAg persists in the absence of active virus replication. HBV DNA is now integrated chromosomally in the hepatocytes. and HBsAg is produced following the transcription of this integrated DNA. This integration of the HBV DNA into the host cell chromosome may be a stage in the development of hepatocellular carcinoma. The integration of the HBV DNA is thought to occur at the time of seroconversion of e Ag.
 

In general e +ve carriers have a high infectivity whereas e -ve carriers have a much reduced or absent infectivity. Over a number of years, it is quite common to see e +ve carriers seroconvert with the development of anti-e Abs and then progress onwards to lose their HBsAg and develop anti-HBs. The rate for the reversion of the carriers to being naturally immune is around 2% per year. In chidren born to carrier mothers, girls are much more likely to seroconvert than boys although both sexes are just as likely to be infected and become carriers initially. It is not unusual for people who were naturally immune with anti-HBs to lose their anti-HBs and develop HBsAg in their blood (especially Haemophiliac patients with AIDS). It is not certain whether this is due to reinfection or the reactivation of the virus.

Chronic HBV carriage may take the form of chronic active hepatitis (CAH) or chronic persistent hepatitis (CPH) or minimal hepatitis. The distinction can only be made on histological examination of the liver. CAH is far more common in e +ve carriers as it is indicative of active viral replication. Cirrhosis and hepatocellular carcinoma (HCC) is thought to be more common in e -ve carriers. It was suggested that those e -ve carriers who had a prolonged e +ve stage are more prone to developing cirrhosis and HCC. It was reported that nuclear DNA is commonly detected alone in the late phase of HBV infection, which represents either integrated fragments or supercoiled HBV DNA, whereas cytoplasmic and nuclear HBV DNA is commonly detected in the early phase of the illness and CAH, which is indicative of active viral replication.

HBV is essentially hepatotropic but HBV DNA has been detected in other sites such as the peripheral leucocytes, the bone marrow and spleen. The viral DNA is usually in episomal form and is rarely integrated. These findings have implications for virus transmission and also for the possible recurrence of hepatitis B infection in patients who have cleared infection in the liver, in particular patients with AIDS who had had anti-HBs following an acute infection in the past but become HBsAg positive again. Individuals infected with both hepatitis B and hepatitis C are prone to prolonged disease, cirrhosis and hepatocellular carcinoma.

LABORATORY_DIAGNOSIS

A battery of ELISAs and RIAs are now available for the diagnosis of specific serological markers of HBV infection.
 

Anti-HBc

HBsAg HBeAg Anti-HBe IgM IgG Anti-HBs Interpretation

  +     +     -       -   -     -     Incubation period

  +     +     -       +   +     -     Acute hepatitis B or persistent carrier state

  +     +     -       -   +     -     Persistent carrier state

  +     -     +      +/-  +     -     Persistent carrier state

  -     -     +      +/-  +     +     Convalescence

  -     -     -       -   +     +     Recovery

  -     -     -       +   -     -     Infection with HBV without detectable HBsAg

  -     -     -       -   +     -     Recovery with loss of detectable anti-HBs

  -     -     -       -   -     +     Immunization without infection. Repeated exposure to antigen without infection,

                                      or recovery from infection with loss of detectable anti-HBc

During the incubation period, HBsAg is the first serological marker to appear. This occurs 2 to 8 weeks before biochemical evidence of liver dysfunction or the onset of jaundice. The antigen persists throughout the course of the illness and is usually cleared from the circulation during convalescence. Next to appear is the viral DNA polymerase and the e antigen. The e antigen is a distinct soluble antigen that is located within the core and correlates closely with the no, of virus particles and the relative infectivity. Anti-HBc is found in the serum 2 - 4 weeks after the appearance of the surface antigen and is always detectable during the acute early phase of the illness. Core IgM become undetectable several months after the onset of uncomplicated acute infection, but core IgG persists for many years, possibly for life. The next antibody to appear is the anti-e. In general, the presence of anti-e is associated with low infectivity of the serum. Anti-Hbs is the last marker to appear late during convalescence.

In general, detection of HBsAg is used for the diagnosis of acute infection and the screening for carrier status. HBeAg is used to assess the potential infectivity of carriers and antibodies to specific antigens indicate past infection and are of value in monitoring progress. Core IgM is of value in diagnosing recent infection in those who have lost detectable antigen and in whom antibodies have not become apparent (termed the diagnostic window). It is possible to get cases where anti-HBs has disappeared whilst anti-HBc persists. It is also possible to have a situation where anti-HBs is present with no anti-HBc with no history of immunization. This may occur in a situation when the person is continually exposed to minute amounts of HBV which is insufficient to set up an infection. In this manner, the patient becomes immune to HBV.

The presence in the serum gene products of the pre-S1 and pre-S2 regions has been found to be associated with high levels of replication. Pre-S proteins have also been found in the liver. The presence of pre-S1 proteins in the serum and in the liver correlates closely with HBV DNA and on cessation of viral replication, pre-S1 is no longer detectable. Antibodies to pre-S2 have been reported as markers of viral clearance and recovery. Furthermore anti-pre-S2 neutralize the infectivity of HBV. These antibodies may be important in the clearance of circulating HBV virions and the termination of infection ; their absence in patients with chronic active hepatitis may explain why infection persists. Other tests which may be of value include ;-

(1) The detection of HBsAg-IgM immune complexes - This has been shown to be of value in predicting the outcome of an acute HBV infection in the sense of whether the patient is likely or not to go onto becoming a carrier. HBsAg-IgM immune complexes should only be present for a few weeks after which they become undetectable. If HBsAg-IgM immune complexes persists for more than a few weeks, then the patient is likely to become a carrier.

(2) Serotyping of the HBsAg - This can be done by the use of monoclonal antibodies. Such typing may provide useful information on the epidemiology of a particular outbreak. However, its usefulness is limited by the low no. of strains of HBsAg so that typing of HBsAg will never provide as much information as phage typing for S.aureus.

HBV-DNA Testing - the determination of HBV DNA has increasing become a routine part of HBV testing, especially for carriers on antiviral therapy and also those with symptoms who are HBeAg -ve i.e. suspected of being infected by core escape mutants. A variety of commercial tests are available that are based on different molecular techniques, including DNA-hybrdization, branched DNA, PCR, Real Time qPCR and LCR. For the purpose of monitoring the response to therapy, it is essential that the same assay is used throughout the whole period.
   

Management

There is no specific therapy for acute hepatitis B. To date, there is no conclusive evidence that early treatment with antiviral agents speeds recovery or reduce the chance of developing chronicity, although trails are ongoing. General measures which apply to all forms of acute hepatitis are as follows ;-

1. Bed rest, hospital admission if required
2. Diet - A good general diet is desirable.
3. Drugs - Although corticosteroids have been advocated in viral hepatitis. Current evidence is that they do not aid recovery and they may have serious side effects.
4. Cases of fulminant hepatic failure - there is no specific treatment but certain measures should be instituted as soon as possible once cerebral changes occur including (i) Nitrogen exclusion diet (ii) Neomycin (iii) Mannitol to reduce cerebral oedema (iv) Close supportive measures.
5. The patient should be monitored by serological tests at regular intervals to check whether on not he has developed carrier status. If so, then treatment with antiviral agents may be considered (see below)

Antiviral Treatment of Chronic Infections

In chronic hepatitis B, treatment may be given to suppress viral replication and the progression of disease. Therapy is not usually recommended for patients with normal enzymes. Therapy is recommended for patients with evidence of active damage to the liver such as raised liver enzymes and evidence of damage seen on liver biopsy. The American Association for the Study of Liver Diseases (AASLD) also recommends the treatment of patients with compensated and decompensated cirrhosis and measurable HBV DNA regardless of e Ag status. Six agents had been recommended by the FDA for treatment of chronic HBV infection: 2 types of interferons and 4 types of nucleoside/nucleotide analogues.

Interferon Therapy

It has been postulated that chronic carriage of HBV is due mainly to inadequate production of interferon and the failure of the body to respond to interferon in the presence of acute HBV infection.  Two preparations of interferons are currently available:  Alpha-Interfron (Intron A) and Peginterferon (Pegasys). In In early clinical trials, interferon therapy is associated with HBeAg loss in 30-40% of patients, and in approximately 10% lost HbsAg altogether. If a patient loses HBeAg loss during interferon therapy, HBsAg loss follows therapy in approximately 80% of patients followed for a decade. In addition, improved survival, complication-free survival, and a reduction in the frequency of hepatocellular carcinoma have been reported in those who responded to interferon. Interferon therapy is more effective in patients with low-level HBV DNA 100,000–40 million copies per mL, elevated ALT (esp if >200 IU/mL), immunocompetence, normal liver function (albumin, bilirubin and coagulation), and acquisition of infection in adulthood. Early studies suggested that the efficacy of interferon was low in patients with pre-core-mutant HBV infection (HBeAg negative strains), but recent observations have renewed interest in interferon for this indication. Emerging data on PEG interferon may result in the first line use of PEG products alone or in combination with oral agents. However, interferon requires inconvenient injection therapy, is associated with a lot of side effects, and is no better than lamivudine in terms eAg seroconversion. Morover, it isof limited value in certain subgroups although it is the only medication that offers a chance at a complete cure.

Other Antiviral Agents

Lamivudine (Epivir-HBV) - This was the first antiviral agent licensed for the treatment of chronic hepatitis B and therefore have the most data available. It is taken orally once a day for at least a year, and is approved for use in both adults and children.   Lamvivudine has now been licensed for the treatment of chronic hepatitis B. Clinical trials with lammivudine as monotherapy have demonstrated that lamvivudine causes a significant reduction in HBV DNA, enhances HbeAg seroconversion, and reduces progression of fibrosis. There are almost no side effects. However, YMDD drug resistant mutants begin to emerge after 36 weeks of therapy. So that at the end of the first year, 15% of strains are resistant, and at the end of the second year, 35% are resistant. However, it appears that the mutant virus is less replicative-competent. Because of the problem with the emergence of mutants, there is intense interest and study on the use of combination therapy.

Adefovir dipivoxil (Hepsera)--- Approved only for adults, it is taken once a day as an oral tablet. Studies have shown that use of adefovir does not induce as much resistance as lamivudine. Clinical trials are being planned in children. In summary, Lamivudine and adefovir have both been shown to be  safe and convenient to take, achieve a 30+% HBeAg loss, histologic improvement in the majority of patients (not limited to HBeAg responders, as is the case for interferon),  Importantly, lamivudine requires longer-duration therapy and is associated with the emergence of viral variants that are rarely seen with adefovir therapy.

Entecavir (Baraclude)--- Approved by the FDA March 30, 2005 fro adults in whom the virus is active and replicating. It is taken as an oral tablet or solution once daily. Entecavir is one of the most potent agents to date with very little side effects reported.  Entecavir can also be used in patients with a resistant virus who have failed lamivudine therapy. HBV is much less likely to develop resistance to entecavir.

Telbivudine (Tyzeka, Sebivo) is a pill taken once a day, with almost no side effects for up to one year. Studies have shown that it rapidly and profoundly suppresses HBV levels. Approved in October 2006 by the FDA for adults. Several clinical trials have reported it to be more effective than lamivudine and adefovir.

Liver transplantation may be an option if the liver is severely damaged.

Prevention

Active_Immunization

Active immunization against HBV is indicated for groups at increased risk of acquiring this infection. These groups include medical personnel involved in the care of patients who are potential carriers, laboratory staff, people working in high risk institutions such as those for the mentally handicapped. Individuals requiring repeated blood transfusions and/or blood products and those who may require haemodialysis in future. The spouses, other sexual contacts, and other family members in close contact of patients with acute hepatitis B or those who are carriers. Women in areas of the world where the carrier rate is high may be considered for immunization in view of the risk of transmitting the infection to their offspring. Infants born to mother with acute infection or carriage should be immunized. Young infants, children and susceptible persons living in areas of the world with a high prevalence of carriers should also be considered.

There were 2 types of vaccine licensed, each containing 20 mg/ml of HBsAg. One is purified from the plasma of carriers, the other is a recombinant protein produced by yeast cells. As of 1991 only the vaccine produced from yeast is licensed. The vaccine has a good overall response rate of 90% (More recent studies suggest that this figure is over-optimistic. The actual percentage of vacinees who do not or make a poor response is probably in the region of 15 -20%). However it is less effective in the immunocompromised and the elderly. 10 to 15% of those aged over 40 do not respond and only 60% of those undergoing maintenance haemodialysis respond. Non-responders should be considered for a booster dose but even then, the response is likely to be poor and HBIG may be necessary should exposure to Hepatitis B occurs. People who are immunodeficient or on immunosuppressive therapy may be given larger doses and/or additional doses of vaccine. The duration of antibody is thought to be 3 to 5 years. Advice on the need for further booster dose have yet to be formulated, but individuals at high risk may wish to determine their Ab levels periodically. If it falls below 100Iu/L then a booster dose should be given. Suitable intervals for testing Ab levels are 1 year and 5 years after vaccination.

Recommendations

The vaccine takes up to 6 months to confer adequate protection and recipients should be advised so. The vaccine should not be given to people who are HBsAg positive, naturally immune or suffering from acute hepatitis B. The vaccine may be given to HIV positive individuals. Screening for HBV markers may be undertaken in a population where the antibody prevalence is high. Groups of individuals considered for vaccination include ;-

(1) Health Care Personnel

1. This include all hospital personnel who may come into contact with hepatitis B patients and those working in the units for the mentally handicapped
2. Laboratory workers and mortuary technicians.
3. Health workers on secondment to areas of the world where there is a high prevalence of HBV
      

(2) Susceptible Patients

1. Patients undergoing haemodialysis - as the response to vaccination is poorer in immunocompromised or older patients, it is recommended that patients with chronic renal damage should be immunised as soon as possible before their disease develops to the stage when they require dialysis or transplant. b

2. Patients on entry to institutions dealing with the mentally handicapped.

3. Haemophiliacs and those receiving regular blood transfusions or blood products.
      

(3) Close Contacts ;-

The spouses or other sexual partners of carriers of hepatitis B (Intimate contacts of individuals suffering from acute hepatitis B and sexual contacts of highly infectious carriers should be given HBIG followed by or simultaneously with active HBV immunisation.)

Consideration should also be given to the following groups of people who are at higher risk of contracting HBV than the general population ;-

1. Police and Emergency Services
2. People visiting other countries for lengthy periods
3. Highly promiscuous individuals, especially homosexuals
4. Inmates of prisons
5. IV drug abusers
6. (Morticians and Embalmers

Dosage and Regimen

The basic regimen consists of 3 doses of vaccine. The first dose is given at an elected date, the second 1 month after the first and the third dose 6 months after the first. An accelerated schedule has also been used with the recombinant vaccine (eg. for travelers) with the third dose given 3 months after the first followed by a booster in 1 year.The vaccine is given i.m. but may be intradermally or s.c. for haemophiliac patients. Post vaccination antibody screening should be done 2 - 4 months after the course of injection.The vaccines are well tolerated generally but rarely symptoms such as fever, rash, malaise, myalgia and arthralgia had been reported. The vaccine can be given to pregnant women at risk as HBV infection carries a severe risk for the mother and the newborn. Vaccination should be postponed in individuals suffering from febrile illnesses. Approximately 50% of individuals will seroconvert (produce anti-HBs of greater than 10 miu/ml) after the first dose, and up to 90% after the second dose. The third dose does not increase numbers of seroconversions significantly and it is meant to be a booster.
   

Passive Immunization

Hepatitis B immunoglobulin (HBIG) is prepared from the pooled plasma with high titre of anti-HBsAg. It may confer temporary immunity of 1 to 3 months if administered under certain conditions. It is used to protect an individual after a single acute exposure to HBV. It is most effective if given within 48 hours of exposure and it should not be given after 7 days following exposure. The dose used is around 600 i.u. in adults and it should be administered as soon as possible after exposure and it is generally recommended that 2 doses of HBIG should be given 30 days apart. HBIG is also given to infants born to e +ve carrier mothers together with active immunization at the same time. It should be given within 12 hours of birth. The chance of the baby developing carrier status is reduced by about 70%. More recent studies using combined active and passive immunization indicate an efficacy approaching 90%.

Hepatitis B immunoglobulin (HBIG) is normally used in combination with hepatitis B vaccine to confer passive and active immunity after exposure. The vaccine and HBIG are given simultaneously at different sites. It has been shown that HBIG does not suppress the active immune response to the vaccine. A single dose of 500 Iu for adults and 200 Iu for the newborn is sufficient for healthy individuals. If infection has already occurred at the time of administration, HBIG can reduce the severity of the disease and prevent the development of the carrier state in many individuals, especially in infants born to mother carriers. Groups requiring post- exposure protection are ;-

1. Infants born to mother who are persistent carriers, especially those who are eAg positive.  The nature and size of the risk at birth varies from persistent carriage in 80 - 90% of infants of HBeAg positive mothers to the less frequent occurrence of hepatitis B infection in infants of anti-HBe positive mothers (around 10%). In countries with high prevalence, HBIG is sometimes given to all babies born to mothers who are HBsAg positive irrespective of HBeAg status. In countries with low prevalence such as the UK, the infants at risk should be identified. The following antenatal mothers should be screened ;-  (i) All ethnic groups other than Caucasian, though Caucasians from Southern and Eastern Europe should also be considered, and (ii) All those with a personal or family history of occupation suggestive of an increased risk of exposure to HBV.

2. Infants born to mothers who are HBsAg positive as a result of recent infection, particularly if HBeAg is detectable and anti-HBe is not.

3. Combined active and passive immunisation is recommended for infants at risk. The first dose of the vaccine should be given at birth or as soon as possible.preferably within 12 hours and not later than 48 hours. HBIG should be given at a contralateral site at the same time.

4. (3) Accidental inoculation or contamination of the eye, mouth or skin with blood or other bodily fluids from a known HBsAg positive individual. Those who have already been vaccinated should be given a booster dose.

5. (4) Sexual Consorts, (and in some circumstances a family contact judged to be at a high risk ) of individuals suffering from acute hepatitis B, and who are seen within one week of jaundice in the contact.
      

HBV and Hepatocellular Carcinoma
   

Hepatocellular carcinoma (HCC) is one of the 10 most common cancers in the world, with over 250000 new cases per year. HCC is more common in males than females and the incidence of the tumour reaches a peak in 30 - 50 age group. The geographical areas with a high incidence of HCC coincides with areas with a high incidence of hepatitis B. Furthermore, most patients with HCC are HBsAg +ve and have high titres of anti-HBc. HBV infection in these areas usually occurs at a young age - in China and S.E.Asia the virus is usually acquired perinatally from a carrier mother whereas in Africa, the infection tends to be acquired in early childhood through horizontal spread of the virus. Therefore there is a long interval before the development of HCC following the initial virus infection. The relative risk of developing HCC in a HBV carrier varies considerably between different ethnic groups, between 40 to 300 fold compared to the normal population. The data on relative risk needs to be reassessed in most studies because many of the subjects had dual hepatitis B and hepatitis C infection.

Analysis by DNA-DNA hybridization reveals integrated HBV DNA in approximately 80% of HCC from HBsAg carriers. It is possible that more sensitive technique such as PCR may lead to a higher rate of detection. There is also an animal model available in the form of hepatomas in woodchucks infected with the woodchuck hepatitis virus.

Mechanisms_for_oncogenesis

primary HCC usually develops in a liver which is affected by chronic hepatitis or cirrhosis and it has been suggested that cirrhosis is the main driving force behind the development of HCC. However, it is clear that HCC is much more likely to develop in an HBV-infected cirrhotic liver than one that is not cirrhotic. Furthermore, HCC can develop in the livers of HBV carriers without an intermediate cirrhotic stage. The finding of integrated viral DNA suggests a direct role for the virus in oncogenesis. In the 20% of cases where HBV DNA is not detected, a 'hit and run' mechanism may be involved. Integrated DNA is commonly found in the liver cells of HBV carriers, especially in e -ve carriers. integrated viral DNA may be detected in both e +ve and e -ve carriers, the time of integration is around the time of seroconversion of the e antigen. The mechanisms involved in HBV induced oncogenesis is still uncertain. It may take the form along the following lines ;-

1. Promoter insertion - This envisages the insertion of a viral promoter in front of a cellular oncogene leading to the transcription of the c-onc. There is little experimental support of this hypothesis.
2. Introduction of a viral coded oncogene - there is no evidence that HBV contain such a gene and it has not been possible to transform cells in vitro using the virus or viral DNA.
3. (Insertions mutagenesis - The integration of the viral genome results in the introduction of an enhancer sequence or a promoter sequence or may disrupt a cellular gene. Again there has been very little experimental evidence.
4. (Transcriptional activation - the X gene of HBV contains a transcriptional activator. This gene may play a role in disrupting the normal transcriptional control of the cell.
    

Hepatitis B Variants

Pre-core mutants

The core/pre-core gene can be translated into either HBcAg or HBeAg. HBeAg is found in the serum and the surface of hepatocytes but not as part of the viral particles. Translation of the pre-core region is only necessary for the production of HBeAg. HBeAg and HBeAg and HBcAg shares antigenic epitopes. However, because of differences in the secondary structures of HBeAg and HBcAg, there are also unique antigenic determinants. Chronic carriers of HBV eventually lose HBeAg and seroconvert to anti-HBe. After an exacerbation of hepatitis, the liver disease becomes quiescent. However, some patients have progressive disease characterised by high concentrations of HBV DNA in serum, and mutant viruses are selected which can no longer produce HBeAg. This process occurs commonly. The most frequent mutation results in a premature stop codon in the pre-core region, terminating the translation of HBeAg. However, the translation of the core protein is not affected.

It is believed that hepatitis is due to the immune-mediated killing of hepatocytes and that HBeAg is an important target. Those hepatocytes that are infected with the pre-core variants will survive the process. This strategy is obviously a potent mechanism to prolong infection. Since HBeAg shares antigenic epitopes with HBcAg, it is postulated that HBeAg plays an important role in inducing immunological tolerance to HBcAg. By this mechanism, infants become chronic carriers without liver damage. However, eventually, the tolerogenic effect will be lost and an immune response will be mounted against HBeAg, resulting in hepatitis and the selection of pre-core mutants.

The pre-core mutant form is also associated with fulminant acute hepatitis. If an anti-HBe positive mother infects her infant, the child is likely to have more severe acute hepatitis than if the mother were HBeAg positive. The mutant had been associated with an outbreak of fulminant hepatitis. These patients are HBeAg negative. The fulminant course may also relate to the proposed tolerising effect of HBeAG. In those patients infected from the beginning with a pre-core mutant, the lack of HBeAg would allow the immune system to destroy hepatocytes in an unrestricted fashion. An alternative explanation is that the patient may be genetically predisposed to mount a very active immune response against the HBeAg producing strain, leading to extensive hepatitis and the rapid selection of the mutant. Fulminant hepatitis does not seem to be as widespread as would be predicted in those countries in which the anti-HBe positive form of chronic hepatitis is common. Perhaps this mutant is not as transmissible as the HBeAg positive strain.

Surface_mutants

Most cases of mutants arise in the "a" determinant of HBsAg. Current vaccines are not thought to be able to protect against infection by this mutant. In addition, there may be problems with the detection of these variants by the current immunoassays
 

CDC hepatitis branch; "Epidemiology and Prevention of Hepatitis A-E: An Overview"
 
 

Hepatitis A-E Slide Set