Multaq : A little background on the virus that causes hepatitis B is essential for understanding the disease, its symptoms, and especially its diagnosis. The existence of hepatitis B virus was discovered by accident in the 1960s. In 1965, Dr. Baruch Blumberg and collaborators discovered a protein of the hepatitis B virus in the blood of an Australian aborigine. This protein was called the Australia antigen. At the time of its discovery, the Australia antigen was not thought to be a viral protein. Over the next few years, however, Dr. Blumberg, his collaborators, and other groups proved that the Australia antigen was associated with hepatitis, specifically a form that was then known as serum hepatitis and was transmitted by blood. Dr. Blumberg was awarded the Nobel Prize in Physiology or Medicine in 1976 for this discovery.
In subsequent years, the hepatitis B virus was photographed under an electron microscope and was propagated in cell culture. Its genetic material was analyzed. A schematic diagram of hepatitis B virus. The hepatitis B virus is a member of the Hepad- naviridae family; other very similar viruses in this family cause liver disease in woodchucks, ground squirrels, and ducks. These animals have served as experimental models for research on hepatitis B.
The genetic material of hepatitis B virus is a circular strand of DNA. This circular DNA encodes four viral proteins, two of which are structural proteins of the viral particle. It is important to be familiar with these proteins, especially the hepatitis B surface and core proteins, because detection of these proteins in the blood, or detection of antibodies against them, plays a critical role in diagnosis.
Hepatitis B core antigen (HBcAg) is a protein that forms the nude- ocapsid, or core, of the viral particle and is associated with the viral DNA. Hepatitis B core antigen is not readily detectable in the blood of infected individuals but can be seen in the liver cells. If the virus is rapidly replicating in the liver, a smaller form of the hepatitis B core antigen can be detected in the infected patient’s blood. This form is known as hepatitis Be antigen (HBeAg). Detection of HBeAg in the blood has important clinical significance in the diagnosis of more serious and more highly contagious disease.
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Acute infection with the hepatitis B virus can cause a wide range of initial conditions, from no symptoms to fulminant hepatic failure. In newborn babies, acute infection, usually transmitted from the mother at the time of delivery, generally does not cause clinical disease. In younger children, acute infection with hepatitis B virus also does not usually cause clinically apparent disease. In adults, most acutely infected individuals develop acute clinical hepatitis that varies in severity.
In most adult cases, acute infection with the hepatitis B virus causes moderate illness that spontaneously resolves, as in Case 1 above. Symptoms of hepatitis typically occur within six to fifteen weeks after infection. Symptoms include nausea, vomiting, fever, right upper quadrant abdominal pain, and jaundice. Blood ALT and AST activities are elevated roughly in proportion to the degree of acute inflammation and liver cell death. Elevations in blood bilirubin concentration and, in more severe cases, prolongation of PT may also occur. About 2 percent of acutely infected adults develop fulminant hepatic failure. This is what happened to the patient described in Case 2. Most of these individuals either die or require emergency liver transplantation. The vast majority of acutely infected adults, as seen in Case 1, have spontaneous resolution of acute hepatitis. About 5 percent of individuals infected as adults go on to develop chronic hepatitis. B, as did the patient in Case 4.
Hepatitis B virus infection is the leading cause of chronic liver disease in the world. Most chronically infected individuals are infected as infants or children. Chronic infection can cause various problems. Some chronically infected individuals are clinically classified as chronic carriers. Chronic carriers have no clinically apparent liver disease; however, this may be an inaccurate term as some so-called chronic carriers exhibit evidence of hepatitis on liver biopsy. Other individuals chronically infected with hepatitis B virus have clinically apparent chronic hepatitis. Long-standing chronic hepatitis resuiting from hepatitis B can lead to cirrhosis. Long-standing hepatitis B infection is also a major risk factor for the development of hepatocellular carcinoma or primary liver cancer, which is the number one or two (along with lung cancer) cause of cancer death worldwide.
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Chronic carriers are considered to be individuals persistently infected with the hepatitis B virus who do not have clinical evidence of hepatitis. The woman described in Case 3 is an example of a chronic carrier. Chronic carriers have detectable HBsAg in their blood but no signs or symptoms of hepatitis or liver disease. The diagnosis is often made during routine screening of pregnant women, as in Case 3, or of blood donors. Typically, blood ALT and AST activities are normal and there is no laboratory evidence of liver damage or dysfunction. The term chronic carrier derives from the fact that these individuals have laboratory evidence of hepatitis B virus infection but no clinical or laboratory evidence of liver disease. About 75 percent of chronic carriers will have no evidence of inflammation on liver biopsy and can truly be called carriers who do not have evidence of chronic hepatitis. About 25 percent of chronic carriers, however, are not really only carriers and will have evidence of inflammation on liver biopsy. These individuals have chronic hepatitis despite normal laboratory tests and no exhibition of symptoms. Some so-called chronic carriers may even have cirrhosis if liver biopsy is performed. Therefore, although almost universally used to describe patients chronically infected with hepatitis B virus and no evidence of liver disease, chronic carrier may not technically be a correct description of all such patients. Furthermore, individuals who are defined as chronic carriers can sometimes develop clinically apparent hepatitis at a later time.
Chronic hepatitis that is clinically apparent, as in the patient described in Case 4, occurs in many individuals chronically infected with the hepatitis B virus. These individuals have detectable serum HBsAg. They may have symptoms of chronic hepatitis including fatigue, depression, loss of appetite, and other nonspecific complaints. Sometimes, the disease is clinically silent and the patient will not have symptoms. Blood tests will usually reveal elevated ALT and AST activities. Sometimes, chronic hepatitis will be diagnosed only by liver biopsy in an individual who is diagnosed clinically as a chronic carrier. •*– Individuals with chronic hepatitis B infection, especially those with evidence of ongoing liver inflammation, are at risk of developing cir rhosis over time. Signs and symptoms of cirrhosis may not be apparent, and the diagnosis may be made only on liver biopsy. Case 4 describes such an example. Some patients with long-standing chronic hepatitis B may not even seek medical attention until they are suffering from complications of cirrhosis
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