https://www.britannica.com/science/hepatitis
Untitled Document
Hepatitis, inflammation of the liver that results from a variety of causes, both infectious and noninfectious. Infectious agents that cause hepatitis include viruses and parasites. Noninfectious causes include certain drugs and toxic agents. In some instances hepatitis results from an autoimmune reaction directed against the liver cells of the body.
Signs and symptoms
The signs and symptoms of acute viral hepatitis result from damage to the liver and are similar regardless of the hepatitis virus responsible. Patients may experience a flulike illness, and general symptoms include nausea, vomiting, abdominal pain, fever, fatigue, loss of appetite, and, less commonly, rash and joint pain. Sometimes jaundice, a yellowing of the skin and eyes, will develop. The acute symptomatic phase of viral hepatitis usually lasts from a few days to several weeks; the period of jaundice that may follow can persist from one to three weeks. Complications of acute viral hepatitis include fulminant hepatitis, which is a very severe, rapidly developing form of the disease that results in severe liver failure, impaired kidney function, difficulty in the clotting of blood, and marked changes in neurological function. Such patients rapidly become comatose; mortality is as high as 90 percent. Another complication is chronic hepatitis, which is characterized by liver cell death and inflammation over a period greater than six months.
Viral causes
Most cases of hepatitis are caused by viral infection. The viruses that give rise to liver inflammation include cytomegalovirus; yellow-feve virus; Epstein-Barr virus; herpes simplex viruses; measles, mumps, and chickenpox viruses; and a number of hepatitis viruses. The term viral hepatitis, however, usually is applied only to those cases of liver disease caused by the hepatitis viruses.
There are seven known hepatitis viruses, which are labeled A, B, C, D, E, F, and G. Hepatitis A, E, and F viruses are transmitted through the ingestion of contaminated food or water (called the fecal-oral route); the spread of these agents is aggravated by crowded conditions and poor sanitation. The B, C, D, and G viruses are transmitted mainly by blood or bodily fluids; sexual contact or exposure to contaminated blood are common modes of transmission.
Hepatitis A
Hepatitis A, caused by the hepatitis A virus (HAV), is the most common worldwide. The onset of hepatitis A usually occurs 15 to 45 days after exposure to the virus, and some infected individuals, especially children, exhibit no clinical manifestations. In the majority of cases, no special treatment other than bed rest is required; most recover fully from the disease. Hepatitis A does not give rise to chronic hepatitis. The severity of the disease can be reduced if the affected individual is injected within two weeks of exposure with immune serum globulin obtained from persons exposed to HAV. This approach, called passive immunization, is effective because the serum contains antibodies against HAV. An effective vaccine against HAV is available and is routinely administered to children over two years of age living in communities with high rates of HAV. The vaccine is also recommended for people who travel to areas where HAV is common, homosexuals, people with chronic liver disease, hemophiliacs, and people who have an occupational risk for infection.
Hepatitis B
Hepatitis B is a much more severe and longer-lasting disease than hepatitis A. It may occur as an acute disease, or, in about 5 to 10 percent of cases, the illness may become chronic and lead to permanent liver damage. Symptoms usually appear from 40 days to 6 months after exposure to the hepatitis B virus (HBV). Those persons at greatest risk for contracting hepatitis B include intravenous drug users, sexual partners of individuals with the disease, health care workers who are not adequately immunized, and recipients of organ transplants or blood transfusions. A safe and effective vaccine against HBV is available and provides protection for at least five years. Passive immunization with hepatitis B immune globulin can also provide protection. Approximately 1 in 10 patients with HBV infection becomes a carrier of the virus and may transmit it to others. Those who carry the virus are also 100 times more likely to develop liver cancer than persons without HBV in their blood.
Hepatitis C
Hepatitis C virus (HCV) was isolated in 1989, at which time it was referred to as non-A, non-B hepatitis. It typically is transmitted through contact with infected blood. Infection may cause mild or severe illness that lasts several weeks or a lifetime; in the early 21st century an estimated 71 million people worldwide had chronic HCV infection. About 80 percent of those who become infected are asymptomatic; those who do show symptoms may experience a flulike illness, with fatigue, nausea, vomiting, and sometimes jaundice. Approximately 60 to 80 percent of chronic infections progress to chronic liver disease, such as cirrhosis or liver cancer. Alcoholics who are infected with hepatitis C are more prone to develop cirrhosis.
Treatment for hepatitis C involves a combination of antiviral medications, namely alpha interferon and ribavirin; however, only about half of those receiving these drugs respond. Other antivirals, such as boceprevir and telaprevir, may be used along with interferon and ribavirin in patients who are infected with a form of hepatitis C known as hepatitis C genotype 1; this therapy typically is reserved for patients in whom the combination of interferon and ribavirin alone is ineffective. Hepatitis C infection can be prevented by avoiding unsafe blood products, needle sharing, and unprotected sex and by exercising caution when seeking tattoos or body piercings. Despite extensive research, a vaccine to prevent HCV infection has remained elusive.
Hepatitis D
Infection with hepatitis D virus (HDV), also called the delta agent, can occur only in association with HBV infection, because HDV requires HBV to replicate. Infection with HDV may occur at the same time infection with HBV occurs, or HDV may infect a person already infected with HBV. The latter situation appears to give rise to a more serious condition, leading to cirrhosis or chronic liver disease. Alpha interferon is the only treatment for HDV infection. Preventing infection with HBV also prevents HDV infection.
Hepatitis E
Discovered in the 1980s, the hepatitis E virus (HEV) is similar to HAV. HEV is transmitted in the same manner as HAV, and it, too, only causes acute infection. However, the effects of infection with HEV are more severe than those caused by HAV, and death is more common. The risk of acute liver failure from infection with HEV is especially great for pregnant women. In less-developed countries, including Mexico, India, and those in Africa, HEV is responsible for widespread epidemics of hepatitis that occur as a result of ingestion of contaminated water or food (enteric transmission).
Hepatitis F and G
Some cases of hepatitis transmitted through contaminated food or water are attributed to the hepatitis F virus (HFV), which was first reported in 1994. Another virus isolated in 1996, the hepatitis G virus (HGV), is believed to be responsible for a large number of sexually transmitted and bloodborne cases of hepatitis. HGV causes acute and chronic forms of the disease and often infects persons already infected with HCV.
Other causes
Most cases of chronic hepatitis are caused by the hepatitis viruses B, C, and D, but other factors such as alcoholism, reaction to certain medications, and autoimmune reactions lead to development of the disease. Chronic hepatitis may also be associated with some illnesses, such as Wilson disease and alpha-1-antitrypsin deficiency. Chronic hepatitis B primarily affects males, whereas chronic hepatitis C arises in equal numbers in both sexes. Autoimmune hepatitis, a disorder associated with a malfunction of the immune system, generally occurs in young women. Treatment for autoimmune hepatitis includes corticosteroids, which help to reduce symptoms.
Alcoholic hepatitis results from sustained consumption of excessive amounts of alcohol. The condition can be reversed if it is caught in its early stages and if the individual either significantly reduces or entirely curtails intake of alcohol. If untreated, it can result in alcoholic cirrhosis.
