There are several types and sub-types of hepatitis (liver inflammation) which are usually classified according to the cause of the disease. This can be broadly divided into :
- Infectious hepatitis, which is inflammation of the liver due to an infection. This may also include certain systemic infections, some of which are uncommon.
- Non-infectious hepatitis, which is inflammation due to various other causes that do not involve an infection like alcohol, medication, toxins and autoimmune factors. This also includes secondary hepatitis which occurs due to other underlying medical conditions.
The terms ‘hepatitis’ is often used to indicate viral hepatitis, of which there are several types. Viral hepatitis is the most common type of hepatitis, however, hepatitis itself may be due to various causes which also need to be considered.
Causes of Different Types of Hepatitis
Viruses are the most common causative pathogen and therefore infectious hepatitis can be divided into viral hepatitis and non-viral hepatitis.
There are five types of hepatitis viruses, which specifically target liver cells (hepatocytes) and are the most common causes of hepatitis.
- Hepatitis A (HAV) is transmitted through contaminated food and drinking water. Transmission via saliva, blood and sexual contact is also possible although the latter is uncommon. It never leads to chronic hepatitis.
- Hepatitis B (HBV) is transmitted through blood, saliva and semen and is often associated with sexual intercourse. Transmission among IV drug users and health care workers (needle-stick injuries) are also fairly common. Often leads to chronic hepatitis.
- Hepatitis C (HCV) is transmitted through blood, saliva and semen. IV drug use, sexual contact and blood transfusions are the more common methods of transmission. Often leads to chronic hepatitis.
- Hepatitis D (HDV) is transmitted through blood and during sexual intercourse and is dependent on previous or existing hepatitis B infection. It can lead to chronic hepatitis.
- Hepatitis E (HEV) is transmitted through drinking water and is more often seen in endemic areas, particularly south and south-east Asia. It does not lead to chronic hepatitis.
Hepatitis G (HGV) is a flavivirus similar to HCV and is transmitted through blood and sexual contact. It is closely associated with HIV (human immunodeficiency virus) infection. HGV does not usually cause any disease in humans and is therefore not considered among the different types of viral hepatitis.
Hepatitis X denotes a type of acute viral hepatitis that cannot be associated with HAV, HBV, HCV, HDV or HEV.
Other types of viruses which cause systemic infections and may lead to hepatitis includes :
- Herpes simplex virus (HSV)
- Epstein-Barr virus (EBV)
- Cytomegalovirus (CMV)
- Yellow fever virus
Other Infections That Cause Hepatitis
Hepatitis caused by other pathogens like bacteria, parasites and fungi are uncommon. These infections may not be isolated to the liver and arise as a result of direct infiltration from neighboring sites, hematogenous or lymphatic spread from distant sites. With fungal infections particularly, causes of immune deficiency like HIV infection also needs to be considered.
Some of these non-infectious causes of hepatitis are sometimes not classified as liver disease. However, it does cause inflammation of the liver and in the true sense of the word, it is hepatitis. Often other organs and systems may be involved to varying degrees.
- Alcoholic hepatitis occurs as a result of years of alcohol misuse. It may be associated with other risk factors such as malnutrition, hepatitis and genetic factors but heavy alcohol consumption is the precipitating factor.
- Drug-induced hepatitis arises with the use of certain medication, particularly chronic medication, like certain antibiotics, antivirals and antiretrovirals for HIV, methotrexate, oral contraceptives and hormone replacement therapy (HRT). There are various other drugs that may also be responsible but the onset of hepatitis with the used of these drugs may be dependent on other individual risk factors. Alcoholic hepatitis and drug-induced hepatitis are also classified under toxic hepatitis.
- Non-alcoholic hepatitis or non-alcoholic steatohepatitis (NASH) is associated with being overweight or obese, particularly in those who are middle aged, but the exact mechanism by which hepatitis arises is unclear. It is also associated with diabetes mellitus (sugar diabetes), insulin resistance and pre-diabetes (impaired glucose tolerance), high blood cholesterol (hypercholesterolemia) and triglycerides (hypertriglyceridemia). However, it may occur in a person without any of these conditions, who is not overweight and obese and may even be seen in children.
- Toxic hepatitis includes liver inflammation caused by alcohol, medication, supplements and exposure to other chemicals. Apart from alcohol and medication, toxic hepatitis may also arise with the use of certain health products, like nutritional supplements and herbal products. It may also be seen with exposure to harsh chemicals, particularly in the industrial setting.
- Autoimmune hepatitis arises due to autoimmune factors, where the body’s immune system attacks the liver cells. The exact cause and mechanism is unknown but it is often associated with other autoimmune disorders affecting various other organs like Hashimoto’s thyroiditis (thyroid gland) and ulcerative colitis (large intestine). There are three sub-types of autoimmune hepatitis designated as type I, II and II autoimmune hepatitis.
- Neonatal hepatitis is seen with in newborns with certain inherited metabolic disorders, bile duct obstruction and biliary defects, and infections. It may also occur for no known reason (idiopathic).