Viral hepatitis are caused by viruses. Viruses are small microorganisms that range from 20–500 nm in diameter and are comprised of one DNA molecule (deoxyribonucleic acid, which contains a complete library of genetic information) or one RNA molecule (ribonucleic acid, which enables cells to read the genetic information). Viruses can only grow and reproduce inside cells. In the case of viral hepatitides, they do it inside liver cells known as hepatocytes.
There are 5 different types of virus that cause viral hepatitides: hepatitis A (HAV), hepatitis B (HBV), hepatitis C (HCV), hepatitis D (HDV) and hepatitis E viruses (HEV).
Hepatitis A virus (HAV). HAV is an RNA virus. It is the most frequent cause of acute hepatitis worldwide, it rarely causes severe hepatitis, it never becomes chronic and the patient recovers spontaneously. Its only reservoir is humans and it is found in contaminated food and water.
Hepatitis B virus (HBV). First discovered in 1963, HBV is a small, partially double-stranded, circular DNA virus. It is not a cytopathic virus, which means it does not cause direct damage to liver cells (hepatocytes). However, HBV can damage the genetic material within liver cells, alter their function and activate the immune system into producing a specific reaction to fight the virus, which subsequently causes liver inflammation and can manifest as either an acute condition or chronic disease.
Hepatitis C virus (HCV). HCV is a small RNA virus identified in 1989. It does not usually produce any symptoms and goes unnoticed by the infected person. In over 80% of cases it transforms into a chronic disease.
Hepatitis E virus (HEV). HEV is another RNA virus. It causes epidemics in Asia and Africa associated with its transmission via contaminated food and water resulting in cases of acute hepatitis. In Europe, however, it has also been found in animals such as pigs and deer. In healthy people, HEV only causes acute hepatitis and they recover spontaneously, but it can develop into chronic hepatitis in immunocompromised patients.