Description
Hepatitis, inflammation of the liver, can be caused by viruses,
bacteria, and other microorganisms, toxic chemicals, alcohol, and
other drugs, but viral hepatitis is the most common cause of hepatitis.
Viral hepatitis is a systemic infection in which virus infects the liver
cells, causing biochemical and cellular changes and interfering with
liver function.
There are a number of different hepatitis viruses (not all identified),
but the primary viruses are types A (HAV), B (HBV), C (HCV), D
(HDV), and E (HEV). HAV and HEV are spread by the fecal-oral route
while types HBV, HCV, and HDV are bloodborne and have similar
characteristics. Researchers estimate that only 10 to 40% of hepatitis
cases are correctly diagnosed as many people have subclinical disease
or non-specific symptoms attributed to other disorders, such as the
flu.
In the United States, HAV, HBV, and HCV account for about 500,000
infections annually, and about 5 million people have chronic infections.
Hepatitis is classified as foodborne (HAV and HEV) or bloodborne.
Food-borne hepatitis viruses do not cause chronic liver disease. HBV
and HCV are of primary concern because they can lead to permanent
damage of the liver and death. Immunizations are only available for
HAV and HBV.
Another hepatitis virus, G (HGV) has been identified, but it rarely
causes hepatitis. HGV is bloodborne and produces a chronic viremia
that lasts about 10 years. Researchers believe that HGV may prolong
survival in those coinfected with HIV and may reduce fibrosis in those
with HCV-HIV coinfection.
About 7.5% of blood donors have a DNA virus designated TT (TTV)
that is readily transmitted through blood transfusions, but as yet no
association between this virus and liver disease has been detected.
Another virus, known as SEN-V has been found in about 2% of blood
donors and is also transmitted through transfusion.