Hepatitis

The liver is the largest organ in the body, occupying the entire upper right quadrant of the abdomen. It performs over 500 vital functions. It processes all of the nutrients the body requires, including proteins, glucose, vitamins, and fats. The liver manufactures bile, the greenish fluid stored in the gall bladder that helps digest fats. One of the liver's major contributions to life is to render harmless potentially toxic substances, including alcohol, ammonia, nicotine, drugs, and harmful by-products of digestion. Old red blood cells are removed from the blood by the liver and spleen, and the iron is cycled to the bone marrow to make new ones. Damage to the liver can impair these and many other processes. Hepatitis is a disorder in which viruses or other mechanisms produce inflammation in liver cells, resulting in their injury or destruction. In most cases this inflammatory process is triggered when the immune system fights off infections caused by viruses. It can also be caused, however, by an overactive immune system that attacks its own liver cells. Inflammation of the liver can also occur from medical problems, drugs, alcoholism, chemicals, and environmental toxins. Hepatitis varies in severity from a self-limited condition with total recovery to a life-threatening or life-long disease.

Experts define hepatitis as short-term (acute hepatitis) or prolonged (chronic hepatitis). In some cases, acute hepatitis develops into a chronic condition, but chronic hepatitis can also occur on its own. Although chronic hepatitis is generally the more serious condition, patients having either condition can experience varying degrees of severity.

Acute hepatitis can begin suddenly or gradually, but it has a limited course and rarely lasts beyond one or two months. Usually there are only spotty liver cell damage and evidence of immune system activity, but on rare occasions, acute hepatitis can cause severe -- even life-threatening -- liver damage.

The chronic forms of hepatitis persist for prolonged periods. Experts usually categorize chronic hepatitis as either (1) chronic persistent or (2) chronic active hepatitis.

Chronic persistent hepatitis is usually mild and nonprogressive or slowly progressive, causing limited damage to the liver. Cell injury in such cases is usually limited to the region of portal tracts, which contains vessels that carry blood to the liver from the digestive tract. In some cases, however, more extensive liver damage can occur over long periods of time and progress to chronic active hepatitis.

If damage to the liver is extensive and cell injury occurs beyond the portal tract, chronic active hepatitis can develop. Significant liver damage has usually occurred by this time. Liver cells are destroyed between the portal tract and the central veins in the liver, and progressive cell damage can build a layer of scar tissue over the liver, resulting in the condition known as cirrhosis. In such cases, the entire liver is threatened with malfunction and failure.

Most cases of hepatitis are caused by viruses that attack the liver; most are named with the letters A through G. It should be noted that the cause of hepatitis is sometimes unexplained, indicating that additional viruses have not yet been discovered.

Hepatitis A, formerly called infectious hepatitis, is always acute and never becomes chronic. The virus is excreted in feces and transmitted in contaminated food and water. Eating shellfish taken from sewage-contaminated water is a common means of contracting hepatitis A. It can also be acquired by close contact with individuals infected with the virus. The hepatitis A virus does not directly kill liver cells, and experts do not yet know how the virus actually injures the liver.

The virus for hepatitis B, formerly called serum hepatitis, is found in semen, blood, and saliva. It is usually spread by blood transfusions, contaminated needles, and sexual contact. Blood screening as reduced the risk from transfusions. The virus does not kill cells directly, but seems to activate cells in the immune system, which cause inflammation and damage in the liver. Hepatitis D virus can replicate only by attaching to hepatitis B and therefore cannot exist without the B virus being present. Between 1% and 10% of hepatitis B patients go on to develop chronic hepatitis and hepatitis B can become chronic without an acute stage.

Hepatitis C was the major cause of all cases of hepatitis resulting from transfusions and most resulting from intravenous drug use. Because of blood screening, the risk from transfusions is now 1 in 10,000. It can also be transmitted through injuries in the skin. It may also be transmitted sexually. About 10% to 60% of acute hepatitis C patients develop the chronic form, which can also occur without a preceding acute stage.

Hepatitis E is similar to hepatitis A and is transmitted by contact with contaminated food or water. It was thought to be rare, but experts now estimate that up to 20% of people in the US may be infected, even those who haven't traveled.

Hepatitis G accounts for about 9% of cases that cannot be diagnosed as hepatitis A through E. It also occurs in about 25% of patients with of hepatitis A, 32% of those with hepatitis B, and 20% of patients with hepatitis C. Hepatitis G appears always to be chronic, but to date indications are that it is mild and does not even increase the severity of any accompanying hepatitis virus.

Hepatitis GB has been discovered as a new distinct form, but it is not known yet whether it causes a serious condition. A number of other common viruses, including herpes simplex, can sometimes injure the liver, although they rarely cause severe hepatitis. Cytomegaloviruses are harmless in most people but can injure the livers in infants and people with impaired immune systems, such as those with AIDS.