The hepatitis B virus is a DNA virus belonging to the Hepadnaviridae family of viruses.
Hepatitis B virus is not related to the hepatitis A virus or the hepatitis C virus.
Some people with hepatitis B never clear the virus and are chronically infected. Approximately 2 billion individuals in the world have evidence of past or present hepatitis B. Many of these people appear healthy but can spread the virus to others.
Hepatitis B infection is transmitted through sexual contact, contact with contaminated blood (for example, through shared needles used for illicit, intravenous drugs ), and from mother to child. Hepatitis B is not spread through food, water, or casual contact.
Injury to the liver by hepatitis B virus is caused by the body’s immune response as the body attempts to eliminate the virus.
Those who acquire the infection in childhood are much more likely to have chronic infection. Chronic hepatitis B may lead to cirrhosis or liver failure. Approximately 15% to 25% of people with chronic infection will die prematurely as a result of the infection.
Progression of chronic hepatitis B viral infection occurs insidiously (subtly and gradually), usually over several decades. The course is determined primarily by the age at which the hepatitis B viral infection is acquired and the interaction between the virus and the body’s immune system.
Liver transplantation should be considered for patients with impending liver failure due to acute (initial) infection or advanced cirrhosis.
Hepatitis B is preventable through vaccination. All children should receive the vaccine. In addition, adults at high risk for hepatitis B should be vaccinated. Unvaccinated people who are exposed to hepatitis B should be evaluated to determine if they need specific immune globulin (HBIG).
The hepatitis B vaccine contains a protein (antigen) that stimulates the body to make protective antibodies. Hepatitis B vaccines are effective and safe. Up to 95% of vaccinated individuals form effective antibodies when they get the vaccine and are protected from hepatitis B.
What is hepatitis?
The term ‘hepatitis’ simply means inflammation of the liver. Hepatitis may be caused by a variety of viruses or other infections, medications, or a toxin such as alcohol. Hepatitis viruses that can cause injury to liver cells in addition to hepatitis B include the hepatitis A and hepatitis C viruses. These viruses are not related to each other or to the hepatitis B virus, and they differ in their structure, the ways they are spread among individuals, the severity of symptoms they can cause, the way they are treated, and the outcome of the infection. Other hepatitis viruses (hepatitis D, hepatitis E, and hepatitis G) cause disease much less commonly.
Other viruses that infect the liver but which are not specifically “hepatitis viruses” include Epstein-Barr virus (EBV, the virus that causes mononucleosis) and cytomegalovirus (CMV).
What is the scope of the problem?
Hepatitis B is an infection of the liver caused by the hepatitis B virus (HBV). It is estimated that 2 billion people worldwide have evidence of current or past hepatitis B infection, including more than 250 million chronic carriers and more than 600,000 deaths worldwide each year, according to the Centers for Disease Control (CDC).
When a person first gets hepatitis B, they are said to have an ‘acute’ infection. Most people are able to eliminate the virus and are cured of the infection. Some are not able to clear the virus and have ‘chronic’ infection with hepatitis B that is usually life-long. Hepatitis B is found throughout the world.
The hepatitis B virus is a DNA virus, meaning that its genetic material is made up of deoxyribonucleic acids. It belongs to a family of viruses known as Hepadnaviridae . The virus is primarily found in the liver but is also present in the blood and certain body fluids.
Hepatitis B virus consists of a core particle (central portion) and a surrounding envelope (outer coat). The core is made up of DNA and the core antigen (HBcAg). The envelope contains the surface antigen (HBsAg). These antigens are present in the blood and are markers that are used in the diagnosis and evaluation of patients with suspected viral hepatitis.
How does hepatitis B virus cause liver injury?
The hepatitis B virus reproduces in liver cells, but the virus itself is not the direct cause of damage to the liver. Rather, the presence of the virus triggers an immune response from the body as the body tries to eliminate the virus and recover from the infection. This immune response causes inflammation and may seriously injure the liver. Therefore, there is a balance between the protective and destructive effects of the immune response to the hepatitis B virus.
How is the hepatitis B virus spread (transmitted)?
Hepatitis B is spread mainly by exposure to infected blood or body secretions. In infected individuals, the virus can be found in the blood, semen, vaginal discharge, breast milk, and saliva. Hepatitis B is not spread through food, water, or by casual contact. Additionally, hepatitis B can be transmitted through sharing toothbrushes and razors contaminated with infected fluids or blood.
Hepatitis B also may be spread from infected mothers to their babies at birth (so-called ‘vertical’ transmission). This is the most prevalent means of transmission in regions of the world where hepatitis B rates are high. The rate of transmission of hepatitis B from mother to newborn is very high, and almost all infected infants will develop chronic hepatitis B. Fortunately, transmission can be significantly reduced through vaccination.
Rarely, hepatitis B can be transmitted through transfused blood products, donated livers and other organs. However, blood and organ donors are routinely screened for hepatitis which typically prevents this type of transmission.
What are the symptoms of acute hepatitis B?
Acute hepatitis B is the period of illness that occurs during the first one to four months after acquiring the virus. Only 30% to 50% of adults develop significant symptoms during acute infection. Early symptoms may be non-specific, including fever , a flu-like illness, and joint pains. Symptoms of acute hepatitis may include:
fatigue , loss of appetite , nausea , jaundice (yellowing of the skin and eyes), and pain in the upper right abdomen (due to the inflamed liver).
Rarely, acute hepatitis damages the liver so badly it can no longer function. This life-threatening condition is called “fulminant hepatitis.” Patients with fulminant hepatitis are at risk of developing bleeding problems and coma resulting from the failure of the liver. Patients with fulminant hepatitis should be evaluated for liver transplantation.
What determines the outcome of acute hepatitis B?
The body’s immune response is the major determinant of the outcome in acute hepatitis B. Individuals who develop a strong immune response to the infection are more likely to clear the virus and recover. However, these patients also are more likely to develop more severe liver injury and symptoms due to the strong immune response that is trying to eliminate the virus. On the other hand, a weaker immune response results in less liver injury and fewer symptoms but a higher risk of developing chronic hepatitis B. People who recover and eliminate the virus will develop life-long immunity, that is, protection from subsequent infection from hepatitis B.
Most infants and children who acquire acute hepatitis B viral infection have no symptoms. In these individuals, the immune system fails to mount a vigorous response to the virus. Consequently, the risk of an infected infant developing chronic hepatitis B is approximately 90%. In contrast, only 6% to 10% of people older than 5 years who have acute hepatitis B develop chronic hepatitis B.
What are the symptoms of chronic hepatitis B?
The liver is a vital organ that has many functions. These include a role in the immune system, production of clotting factors, producing bile for digestion ; storing nutrients including sugars, fats and minerals for use by the body later; processing medications; and breaking down toxic substances. Patients with chronic hepatitis B develop symptoms in proportion to the degree of abnormalities in these functions. The signs and symptoms of chronic hepatitis B vary widely depending on the severity of the liver damage. They range from few and relatively mild signs and symptoms to signs and symptoms of severe liver disease (cirrhosis or liver failure).
Most individuals with chronic hepatitis B remain symptom free for many years or decades. During this time, the patient’s liver function blood tests usually are normal or only mildly abnormal. Some patients may deteriorate and develop inflammation or symptoms, putting them at risk for developing cirrhosis.
Inflammation from chronic hepatitis B can progress to cirrhosis (severe scarring) of the liver. Significant amounts of scarring and cirrhosis lead to liver dysfunction.
Symptoms may include:
weakness, fatigue , loss of appetite, weight loss , breast enlargement in men, a rash on the palms,
difficulty with blood clotting, and spider-like blood vessels on the skin.
Decreased absorption of vitamins A and D can cause impaired vision at night and thinning of bones ( osteoporosis ). Patients with liver cirrhosis also are at risk of infections because the liver plays an important role in the immune system.
In patients with advanced cirrhosis, the liver begins to fail. This is life-threatening condition.
Several complications occur in advanced cirrhosis: Confusion and even coma ( encephalopathy ) results from the inability of the liver to detoxify certain toxic substances. Increased pressure in the blood vessels of the liver ( portal hypertension ) causes fluid to build up in the abdominal cavity ( ascites ) and may result in engorged veins in the swallowing tube (esophageal varices) that tear easily and may cause massive bleeding.
Portal hypertension can also cause kidney failure or an enlarged spleen resulting in a decrease of blood cells and the development of anemia , increased risk of infection and bleeding.
In advanced cirrhosis, liver failure also results in decreased production of clotting factors. This causes abnormalities in blood clotting and sometimes spontaneous bleeding.
Patients with advanced cirrhosis often develop jaundice because the damaged liver is unable to eliminate a yellow compound, called bilirubin.
Patients with chronic hepatitis B are at risk of developing liver cancer .
Symptoms of liver cancer are nonspecific. Patients may have no symptoms, or they may experience abdominal pain and swelling, an enlarged liver , weight loss , and fever . The most useful diagnostic screening tests for liver cancer are a blood test for a protein produced by the cancer called alpha-fetoprotein and an ultrasound imaging study of the liver. These two tests are used to screen patients with chronic hepatitis B, especially if they have cirrhosis or a family history of liver cancer.
Rarely, chronic hepatitis B infection can lead to disorders that affect organs other than the liver. These conditions are caused when the normal immune response to hepatitis B mistakenly attacks uninfected organs.
Among these conditions are:
Polyarteritis nodosa : a disease characterized by inflammation of the small blood vessels throughout the body. This condition can cause a wide range of symptoms, including muscle weakness, nerve damage, deep skin ulcers, kidney problems, high blood pressure , unexplained fevers, and abdominal pain .
Glomerulonephritis: another rare condition, which is inflammation of the small filtering units of the kidney.
Hepatitis B virus DNA:
The best marker of hepatitis B virus reproduction is the level of hepatitis B virus DNA in the blood. Detection of hepatitis B virus DNA in a blood sample signals that the virus is actively multiplying. In acute hepatitis, HBV DNA is present soon after infection, but is eliminated over time in patients’ who clear the infection. In chronic hepatitis, levels of HBV DNA often continue to be elevated for many years and then decrease as the immune system controls the virus. HBV DNA levels are sometimes referred to as the ‘viral load’.
What is delta hepatitis?
Delta hepatitis is caused by a virus that only infects people who already have hepatitis B. The delta hepatitis virus (also known as hepatitis D or HDV) is an RNA virus, meaning that its genetic material is made up of ribonucleic acid. It is spread through exposure to contaminated blood, especially with illicit, intravenous drug use, and by sexual contact. Delta hepatitis can be acquired at the same time as acute hepatitis B. When this happens, infected people are quite sick but more than 95% are eventually able to eliminate the viruses from their bodies. People who already have chronic hepatitis B can acquire delta hepatitis as well. This often causes severe inflammation of the liver, and the viruses are less likely to be cleared.
Delta hepatitis makes chronic hepatitis B much worse. It increases the risk of complications, especially cirrhosis, which occurs in up to two-thirds of patients. There is no vaccine against delta hepatitis.
What about co-infection with hepatitis B virus and hepatitis C virus?
Hepatitis C is caused by a virus that is spread through contaminated needles or blood products and, less commonly, through sexual intercourse. About 10% of patients with chronic hepatitis B also are co-infected chronically with hepatitis C virus ( HCV ). The two viruses interfere with each other and one usually predominates. If hepatitis C is the predominant infection, treatment is directed against the hepatitis C. Patients infected with both viruses are at higher risk for complications of liver disease. There is no effective vaccine against hepatitis C. People with hepatitis C should be vaccinated against hepatitis B to prevent co-infection.
What happens in co-infection with hepatitis B virus and HIV?
The human immunodeficiency virus ( HIV ) and hepatitis B virus are transmitted in similar ways, and it is not uncommon for an individual to have both infections. People with HIV who acquire hepatitis B are more likely to become chronically infected with hepatitis B than people who do not have HIV. The reason for this is thought to be that HIV suppresses the immune system and impairs the ability of the body to eliminate the hepatitis B virus.
What is the role of liver transplantation in hepatitis B?
Liver transplantation has been successful in patients who have irreversible, life-threatening complications of hepatitis B. This includes patients with liver failure due to end-stage cirrhosis or unusually severe (fulminant) hepatitis. Liver transplantation does not cure hepatitis B, and hepatitis may occur in the new liver.
What can be done to prevent hepatitis B?
Hepatitis B is a preventable disease. Vaccination and post-exposure prophylaxis have significantly reduced rates of infection. Risk can also be reduced by avoiding unprotected sex, contaminated needles, and other sources of infection.
How is transmission of hepatitis B virus from mother to newborn infant prevented?
Infected mothers can pass hepatitis B to their newborn infants. All pregnant women should have their blood tested to determine if they are infected. Infants born to infected mothers should receive HBIG and hepatitis B vaccine at birth. This is 85% to 95% effective in eliminating the risk of hepatitis B in the infant.