Viral Hepatitis: Definition and Overview of the (A, B, C, D, E, G)
Hepatitis means inflammation of the liver. Many illnesses and conditions can cause inflammation of the liver, for example, drugs, alcohol, chemicals, and autoimmune diseases. Many viruses, for example, the virus causing mononucleosis and the cytomegalovirus, can inflame the liver. The focus of this article is on these viruses that cause the majority of human viral hepatitis.
Most viruses, however, do not attack primarily the liver; the liver is just one of several organs that the viruses affect. When most doctors speak of viral hepatitis, they are using the definition that means hepatitis caused by a few specific viruses that primarily attack the liver and are responsible for about half of all human hepatitis.
There are several hepatitis viruses; they have been named types A, B, C, D, E, F (not confirmed), and G. As our knowledge of hepatitis viruses grows, it is likely that this alphabetical list will become longer. The most common hepatitis viruses are types A, B, and C. Reference to the hepatitis viruses often occurs in an abbreviated form (for example, HAV, HBV, HCV represent hepatitis viruses A, B, and C, respectively.)
Hepatitis viruses replicate (multiply) primarily in the liver cells. This can cause the liver to be unable to perform its functions. The following is a list of major functions of the liver:
- The liver helps purify the blood by changing harmful chemicals into harmless ones. The source of these chemicals can be external, such as medications or alcohol, or internal, such as ammonia or bilirubin. Typically, these harmful chemicals are broken down into smaller chemicals or attached to other chemicals that then are eliminated from the body in the urine or stool.
- The liver produces many important substances, especially proteins that are necessary for good health. For example, it produces albumin, the protein building block of the body, as well as the proteins that cause blood to clot properly.
- The liver stores many sugars, fats and vitamins until they are needed elsewhere in the body.
- The liver builds smaller chemicals into larger, more complicated chemicals that are needed elsewhere in the body. Examples of this type of function are the manufacture of a fat, cholesterol, and the protein bilirubin.
When the liver is inflamed, it does not perform these functions well, which brings about many of the symptoms, signs, and problems associated with any type of hepatitis. Each hepatitis viral type (A-F) has both articles and books describing the details of infection with that specific virus. This article is designed to give the reader an overview of the predominant viruses that cause viral hepatitis, their symptoms, diagnosis, and treatments, and should help the reader choose the subject(s) for more in-depth information.
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What are the common types of viral hepatitis?
Although the most common types of viral hepatitis are HAV, HBV, and HCV, some clinicians had previously considered the acute and chronic phases of hepatic infections as “types” of viral hepatitis. HAV was considered to be acute viral hepatitis because the HAV infections seldom caused permanent liver damage that led to hepatic (liver) failure. HBV and HCV produced chronic viral hepatitis. However, these terms are outdated and not currently used as frequently because all of the viruses that cause hepatitis may have acute phase symptoms (see symptoms below). Prevention techniques and vaccinations have markedly reduced the current incidence of common viral hepatitis infections.
Hepatitis A (HAV)
Hepatitis caused by HAV is an acute illness (acute viral hepatitis) that never becomes chronic. At one time, hepatitis A was referred to as “infectious hepatitis” because it could be spread easily from person to person like other viral infections. Infection with hepatitis A virus can be spread through the ingestion of food or water, especially where unsanitary conditions allow water or food to become contaminated by human waste containing hepatitis A (the fecal-oral mode of transmission). Hepatitis A typically is spread among household members and close contacts through the passage of oral secretions (intimate kissing) or stool (poor hand washing). It also is common to have infection spread to customers in restaurants and among children and workers in daycare centers if hand washing and sanitary precautions are not observed.
Hepatitis B (HBV)
HBV hepatitis was at one time referred to as “serum hepatitis,” because it was thought that the only way HBV could spread was through blood or serum (the liquid portion of blood) containing the virus. It is now known that HBV can spread by sexual contact, the transfer of blood or serum through shared needles in drug abusers, accidental needle sticks with needles contaminated with infected blood, blood transfusions, hemodialysis, and by infected mothers to their newborns. The infection also can be spread by tattooing, body piercing, and sharing razors and toothbrushes (if there is contamination with infected blood). About 5% to 10% of patients with HBV hepatitis develop chronic HBV infection (infection lasting at least six months and often years to decades) and can infect others as long as they remain infected. Patients with chronic HBV infection also are at risk of developing cirrhosis, liver failure, and liver cancer. It is estimated that there are 2.2 million people in the U.S. and 2 billion people worldwide who suffer from chronic HBV infections.
Hepatitis C (HCV)
HCV hepatitis was previously referred to as “non-A, non-B hepatitis,” because the causative virus had not been identified, but it was known to be neither HAV nor HBV. HCV usually is spread by shared needles among drug abusers, blood transfusion, hemodialysis, and needle sticks. Approximately 75%-90% of transfusion-associated hepatitis is caused by HCV. Transmission of the virus by sexual contact has been reported but is considered rare. An estimated 75% to 85% of patients with acute HCV infection develop chronic infection. Patients with chronic HCV infection can continue to infect others. Patients with chronic HCV infection are at risk for developing cirrhosis, liver failure, and liver cancer.Types D, E, and G Hepatitis
There also are viral hepatitis types D, E, and G. The most important of these at present is the hepatitis D virus (HDV), also known as the delta virus or agent. It is a small virus that requires concomitant infection with HBV to survive. HDV cannot survive on its own because it requires a protein that the HBV makes (the envelope protein, also called surface antigen) to enable it to infect liver cells. The ways in which HDV is spread are by shared needles among drug abusers, contaminated blood, and by sexual contact; essentially the same ways as HBV.
Individuals who already have chronic HBV infection can acquire HDV infection at the same time as they acquire the HBV infection, or at a later time. Those with chronic hepatitis due to HBV and HDV develop cirrhosis (severe liver scarring) rapidly. Moreover, the combination of HDV and HBV virus infection is very difficult to treat.
Hepatitis E virus (HEV) is similar to HAV in terms of disease and mainly occurs in Asia where it is transmitted by contaminated water.
Hepatitis G virus (HGV, also termed GBV-C) was recently discovered and resembles HCV, but more closely, the flaviviruses. The virus and its effects are under investigation, and its role in causing disease in humans is unclear.
Source: medicinenet
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