What is hepatitis?
The five hepatitis viruses (hepatitis, A, B, C, D, and E) belong to five different virus families and are genomically distinct with different replication strategies. They also have different clinical features and outcomes. Viral hepatitis is a liver disease that is caused by exposure to one of the five hepatitis viruses (hepatitis, A, B, C, D, and E). Each virus is named after a letter of the alphabet, hepatitis A through E. Though other viruses can cause hepatitis, only the five are considered hepatitis viruses.
Hepatitis A virus (HAV) and hepatitis E virus (HEV) infections are transient and are transmitted by the oro–faecal route. Hepatitis B virus (HBV) and hepatitis C virus (HCV) and hepatitis delta virus (HDV) can be transient or chronic, and are transmitted by the parenteral route. There are also differences in the mechanisms of infection; for example they use different receptors to gain entry into the hepatocytes, use different mechanisms to establish chronic infection, and their mechanisms of pathogenicity differ.
People are usually exposed to hepatitis A by eating or drinking something contaminated with the virus. When someone is sick with hepatitis A, the person will pass the virus along in his or her stools. In developing countries with poor sanitation systems, infected stools can contaminate an entire water supply. Good hygiene and avoiding contaminated food and water is a great defense, but the best protection is to get the hepatitis A vaccine — which is especially recommended prior to traveling to places without a secure water supply.
Transmission of HBV is primarily from blood or blood-derived products. HBV is the most prevalent of the three viruses known to ensure chronic hepatitis (HCV and HDV) being the other two. HBV has a double shell. The outer shell is the viral envelope consisting of HBsAg. The inner shell consists of hepatitis B core antigen (HBcAg) enclosing the viral genome. HBV is abundant in the blood during infection and in some stages of chronic infection with titres of up to 1010/ml.
Most HCV infections are chronic. HCV belongs to hepacivirus genus of flaviviridae which includes yellow fever, dengue, West Nile and Japanese encephalitis viruses. They possess much similarity in their genomic structure and replication strategy. Symptoms for HCV are similar to other types of hepatitis, and like HBV, a blood test is needed for diagnosis. Both HBV and HCV increase a person’s risk for liver cancer.
HDV does not encode its own envelope protein and depends on HBV for its transmission. It has an outer coating of HBsAg underneath which is HDVAg protein and RNA. Based on the genetic sequence HDV has been classified into three genotypes. Hepatitis D causes swelling of the liver. Preventing hepatitis B by being vaccinated and avoiding blood and body fluid exposure is the best way to prevent getting hepatitis D.
HEV has been responsible for major outbreaks of acute hepatitis in developing countries. A unique characteristic of HEV infection is high mortality in among pregnant women in third trimester. This type of hepatitis doesn’t often occur in the U.S. It causes swelling of the liver, but no long-term damage. It can also be spread through oral-anal contact.