"As a consequence of disease and environmental forces, as well as other factors, a large number of polymorphisms may exist in a population. Some may be related to present selective forces, and others to forces which operated in the past, but which are no longer significant. Present gene frequencies may also result from gene mixture between populations."

“Viral hepatitis is an inflammation of the liver caused by at least six different, mostly unrelated, viruses . It can occur in an acute form from which most patients experience a complete recovery. Acute viral hepatitis is characterized by an insidious onset, often with fever and severe malaise and loss of appetite for food, alcohol, and tobacco. Flu-like symptoms may occur early in the illness. The characteristic finding that occurs in many cases is the development of jaundice, a dramatic yellow discoloration of the skin and other surfaces. Symptoms may last for days or weeks. The acute disease usually results in complete recovery with lifelong immunity. Occasionally, acute hepatitis may advance to the fulminant phase; the patient does not recover, but develops liver failure and death may be rapid. Fortunately, this is rare. Hepatitis due to HAV and HEV is nearly always acute. Acute disease also may occur with HBV and probably HGV. HCV is usually chronic.”

“Primary cancer of the liver is one of the most common cancers worldwide; HBV is the major cause of HCC. A vaccine that protects against HBV infection was invented in 1969 and is now one of the most commonly used vaccines. National vaccination programs have dramatically reduced the prevalence of HBV infection and carriers, with a concomitant decrease in the incidence of HCC in the vaccine-impacted populations. HBV vaccine is the first widely used cancer prevention vaccine; a second that protects against papilloma virus and cancer of the cervix has recently been introduced.”