Hepatitis B Virus (HBV) Antigen, Antibody, Vaccine, Carrier
The liver is an important organ that is responsible for several different functions, particularly the processing of nutrients, wastes and other substances. Hepatitis is the term for inflammation of the liver and may be due to infectious or non-infectious causes. The five types of hepatitis viruses are common infectious causes of liver inflammation, and some like hepatitis A (HAV), B (HBV) and C (HCV) are more frequently seen infectious agents. Inflammation may eventually lead to death of the liver cells (hepatocytes) which severely compromises normal liver function.
What is the hepatitis B virus (HBV)?
The hepatitis B virus (HBV) can infect the liver cells resulting in an acute infection or persist with chronic inflammation of the liver. It is also one of the most common causes of hepatocellular carcinoma (liver cancer). HBV spread occurs through contact with the bodily fluids of an infected person and this includes sexual transmission. A person with hepatitis B can be asymptomatic for long periods of time but may still be a carrier and spread the virus among different contacts.
The hepatitis virus consists of a core containing DNA (HBV-DNA) with an enzyme known as DNA polymerase that assists with viral replication and is surrounded by surface proteins (HBsAg). Two other proteins within the core include the nucleocapsid core protein, HBcAg which stays within the infected liver cells for the assembly of new viruses. Another protein in the core known as HBeAg is released into the bloodstream during active viral replication.
HBV infection may lead to one of the following states :
- Acute hepatitis with subsequent recovery and total clearance of the virus in a person with a healthy immune system.
- Non-progressive chronic hepatitis which may occur after an acute infection.
- Fulminant hepatitis with destruction of large parts of the liver is life-threatening. It is very rarely seen with an acute infection band is more likely to occur in an immunocompromised patient.
- Asymptomatic carrier state.
Transmission of HBV
Health workers, IV drugs users and commercial sex workers are at a higher risk of HBV infection due to needle-stick injuries, sharing used needles and sexual intercourse respectively. The use of contaminated tattoo needles, acupuncture needles, and transmission from close contact with an infected person with cuts are fairly uncommon modes of horizontal transmission these days. Perinatal transmission (vertical transmission) is still high, particularly in developing countries.
Signs and Symptoms of Hepatitis B Infection
Almost half of the patients with an acute infection will be asymptomatic. In chronic hepatitis B infection, the patient may be asymptomatic for long periods of time until there is severe damage to the liver.
Acute HBV Infection
Acute hepatitis B lasts for less than 6 months. The early symptoms may resemble the flu – fever, muscle aches, joint pains and a general feeling of being unwell. More specific symptoms, when present, includes :
- Upper right abdominal pain (read more on liver pain location)
- Nausea and vomiting
- Dark urine
- Loss of appetite
Chronic HBV Infection
Chronic hepatitis B is seen where the virus does not clear and the infection persists past 6 months.The clinical features of chronic HBV infection depends on the degree of liver damage. This can progress over decades and eventually lead to cirrhosis and liver cancer. The clinical features therefore correspond to liver dysfunction seen in these conditions. Recurrence of the infection (flare) may be symptomatic for short periods, similar to acute HBV. Some of the signs and symptoms that may be noticed includes :
- Weight loss
- Abdominal pain
- Abdominal swelling
- Enlarged liver (hepatomegaly), spleen (splenomegaly) or both (hepatosplenomegaly)
- Confusion (encephalopathy)
A carrier is a person with chronic hepatitis B showing no symptoms of the infection and there is no damage to the liver. However the person may still be able to infect contacts. This is also referred to as chronic inactive hepatitis B. In this state, the virus is sometimes cleared from the body after several years.
Hepatitis B Antigens and Antibodies
Viral proteins (antigens) trigger the immune system to produce corresponding antibodies. When these antibodies bind with the antigens it helps to direct the activity of immune cells.
Hepatitis B Surface Antigen (HBsAg) and Antibody (anti-HBs)
The surface proteins surrounding the viral core is known as the hepatitis B surface antigen (HBsAg). If detected by a blood test, then it is an indicator of an active infection. HbsAg is detectable within 3 to 4 weeks of the infection and possibly up to 5 months in an acute infection. If the antigen is still detectable after 6 months, then it is indicative of a chronic infection.
The antibody to HBsAg (anti-HBs) and can be detected after 3 to 6 months. It is often detectable for several years or even throughout life. Anti-HBs may be detected with a previous infection or vaccination and this can be verified by the presence of anti-HBc (discussed below).
Hepatitis B Core Antigen (HBcAg) and Antibody (anti-HBc)
The hepatitis B core antigen itself is not detectable in the blood of an infected person at any time. However, the antibody formed against it (anti-HBc) can be detected soon after infection and rapidly rises, then is followed by a gradual decline but persists over the long term. Anti-Hbc is evident in an infection but not with a vaccination and can therefore help to differentiate whether the presence of anti-HBs is due to an infection or vaccination.
The IgM type of anti-HBc may also be present when the surface antigen (HBsAg) is no longer detectable in an acute infection, even before the surface antibody (anti-HBs) is present in the blood. The IgG type of anti-HBc along with HBsAg is indicative of a chronic infection.
Hepatitis B e Antigen (HBeAg) and Antibody (anti-HBe)
Another protein that is found in the viral core is known as the hepatitis B e-antigen (HBeAg) and unlike the other core protein (HBcAg), it is detectable in the bloodstream. HBeAg is indicative of viral replication in the liver and antibodies against it (anti-HBe) form soon afterwards.
Hepatitis B Vaccine
Vaccination is recommended for infants and children. High risk adults who have not been vaccinated in childhood should consider immunization. Hepatitis B vaccination involves three intramuscular injections. The second vaccine is given one month after the first shot and the third is administered six months after the first shot. Side effects from the hepatitis B vaccine is uncommon. Usually it is mild and may include soreness at the site of administration and mild fever. Very rarely, severe allergic reactions to the vaccine may arise but is unlikely to be life-threatening.
Treatment for Hepatitis B
Treatment options are limited and therefore the focus should be on prevention, particularly via immunization in high risk individuals. Within the first 24 hours of exposure, hepatitis B immunoglobulins may be administered to help fight off the infection. However, contacts may not seek medical assistance at such an early stage and it may not be effective in every case. For acute infections, supportive treatment for the infected person may be all that is necessary and the infection resolves on its own. Antiviral medication (nucleoside/nucleotide analogues, interferons) may be recommended for chronic hepatitis and immunocompromised patients. Ultimately the damage to the liver can be so severe that a liver transplant may be the only option.