By Clare Knight, B.Sc. Reviewed by Emily Henderson, B.Sc.
Hepatitis is a general term to describe inflammation of the liver tissue. It can arise from several causes, although the commonest cause is a viral infection. Globally, approximately 2.3 billion people are infected with hepatitis viruses, resulting in 1.4 million deaths annually.
Hepatitis. Image Credit: Explode/Shutterstock.com
Causes of hepatitis
Non-viral causes
Although viral forms of hepatitis account for more than 90% of cases, they can arise from non-viral factors including alcohol abuse, autoimmune disease, and medication use. Alcoholic hepatitis is associated with over-consumption of alcohol over a prolonged time, caused by the metabolism of ethanol (the chemical term for alcohol).
Autoimmune hepatitis occurs when the body’s immune response produces autoantibodies, immune proteins which mistakenly target and attack the body’s own cells and organs. Medication-induced hepatitis results from ingesting a toxic amount of medicine. It occurs when the liver becomes damaged because of attempting to break down the medication in the bloodstream. Some medications accumulate damage to the liver over time, whilst others such as acetaminophen (paracetamol) can lead to hepatitis after a single overdose.
Viral causes
Viral hepatitis is a serious public health concern, infecting millions of people worldwide each year. The World Health Organization (WHO) in 2015 estimated that 1 in 3 people globally is infected with viral hepatitis, most commonly with hepatitis B or C. The five viruses that account for almost all cases of hepatitis include:
Hepatitis A (HAV)
Prevalent in areas without access to safe drinking water, HAV is present in the feces of infected patients and is transmitted via contamination of food and water, and some sexual activities. Infected people will firstly present with fever, gastrointestinal symptoms, myalgias, and tiredness before developing jaundice. Clinical manifestation varies significantly with age: children aged up to 6 years tend to be asymptomatic.
Annually, approximately 1.5 million cases of HAV are recorded, although infections are thought to be greatly underreported. It is highly endemic to low-income countries where the lifetime prevalence of infection in up to 90%. In these high endemic countries, nearly all children are infected during infancy or early childhood, develop no symptoms and acquire lifelong immunity. In high-income countries, HAV endemicity is less than 50%. Death from HAV is extremely rare.
Hepatitis B (HBV)
Globally, HAB is one of the most common, yet severe transmissible diseases, with 5% of those infected progressing to serious liver disease, cancer, and death. The virus is transmitted via bodily secretions such as blood, semen, and vaginal secretions, and is more infectious than HIV.
For many decades, rates of new HVB infectious in the United States were in decline, but this progress has stalled following the epidemic of opioid use across America.
Hepatitis C (HCV)
The HVC virus is transmitted via blood, even in microscopic amounts. Although manifestations of the virus can vary from a mild and short-lived illness to a serious and chronic infection, over 50% of people who become infected with the virus will develop a chronic disease., between 5% and 25% will go on to develop cirrhosis of the liver.
As it is estimated that approximately 50% of with HPC do not know they are infected, testing for the virus is encouraged among high-risk groups. These groups include intravenous drug users, all pregnant women (owing to the risk of transmission to the child), those who received blood products or organs before the mid-1990s, and all medical staff after needlestick injuries.
Hepatitis D (HDV)
HVD is a type of hepatitis that can only occur in the presence of HVB. This is because it is a satellite subviral agent. This means it can only multiply if in the presence of HVB and cannot survive without HVB because it relies on the surface antigen produced by HVB to infect liver cells.
Transmission of HVD can occur either via coinfection with HVB or if it becomes superimposed onto HVB. This process is called superinfection and occurs when a cell that was previously infected with one virus, gets infected with another virus at a later point in time.
Superinfections can be more resistant to antiviral drugs and the body’s immune response. Patients who become infected with both HVB and HVD develop cirrhosis of the liver at a faster rate, and as such, the co-infection is difficult to treat.
Hepatitis E (HEV)
HVE is similar to HVA, both in the mode of transmission, the severity of illness, and its self-limiting nature. It is endemic to developing countries with a higher risk of food and water contamination: in Northern America and Europe, infections are typically attributed to travel. However, there is increasing evidence that it may be transmitted via the consumption of processed pork products and contact with pigs.
Hepatitis F & G?
The hypothesis of hepatitis F followed the development of testing for HVC and HVE when it became clear that there were some cases of hepatitis that could not be classified as A-E. In the 1990s, a study that identified a novel virus in the stool of non-hepatitis A-E transplant patients, found when the novel virus particles when injected into monkeys, led to hepatitis.
However, the existence of the virus has not been substantiated. More recent research has identified a new virus, closely related to HVC, which is transmissible via blood but leads to a mild infection.
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