Hepatitis was traditionally separated into two types based on clinical and epidemiological characteristics: type A caused by the hepatitis A virus (HAV) and type B caused by the hepatitis B virus (HBV).
Hepatitis C virus (HCV) cannot be cultivated, and it was only through recombinant DNA technology that a diagnostic test was devised to identify hepatitis C as the major cause of what had previously been termed non-A non-B (NANB) hepatitis.
Transmission of hepatitis A is via the faecal-oral route, through contaminated food or water. Thorough cooking will destroy the virus, but shellfish, which are usually eaten raw, may become infected from sewage contaminated seawater and become a vehicle for transmission.
Hepatitis B is transmitted parenterally and sexually. Transmission most commonly occurs following sexual intercourse, as a result of blood to blood contact, including injury with contaminated sharp instruments or other equipment by intravenous drug misusers, or by perinatal transmission from mother to child.
Transfusion-associated infection is now rare and adequate treatment of blood products has eliminated these as sources of infection in the UK. A hepatitis B vaccine is available and routine immunisation of at-risk groups is recommended. These include certain groups of health care workers, babies born to hepatitis B positive mothers and injecting drug users.
Infection with hepatitis C virus is associated with intravenous drug use or blood products. Sexual, vertical and occupational transmission do occur, but on a less frequent basis than HBV. Transfusion associated infection is now rare in the UK. A vaccine for hepatitis C is not available.
Other hepatitis viruses have been identified. Hepatitis D is always associated with co-infection of HBV. Hepatitis E, like HAV, is transmitted by the faecal-oral route, often associated with gross contamination of water supplies (usually by sewage).