few and mild to severe with pain, fever,
and jaundice. Blood tests, including liver
function tests, may be used for diagnosis.
In most cases of acute viral hepatitis,
natural recovery occurs within a few
weeks. If the disorder is caused by expo-
sure to a chemical or drug, detoxification
using an antidotemay be possible. In-
tensive caremay be required if the liver
is badly damaged. Rarely, a liver trans-
plantis the only way of saving life. In all
cases, alcohol should be avoided.
hepatitis BFormerly known as serum
hepatitis, this disorder is due to the hep-
atitis B virus, which is transmitted in
infected blood, blood products, or other
body fluids, often through contact with
needles, blood transfusions, or sexual
contact.After an incubation period of 1–6
months, the onset of symptoms, such as
headache, fever, and jaundice, is sudden.
Most patients recover, but hepatitis B
can be fatal. A vaccine is available.
In about 5 percent of cases, the virus
continues to cause inflammation and can
still be detected in the blood 6 months
after infection. People who suffer from
persistent infection are at long-term risk
of liver cancerand cirrhosisand may be
treated with interferon.
hepatitis C Caused by the hepatitis C
virus and formerly known as non-A non-B
hepatitis, this infection is often trans-
mitted through sharing needles. Blood
transfusions no longer pose a signifi-
cant risk because of blood screening.
Hepatitis C has an incubation period
of 6–12 months and begins as a mild
illness which may go undetected. In
about 3 in 4 patients, chronic hepatitis
develops (see hepatitis, chronic), which
can progress to cirrhosisof the liver and
an increased risk of hepatoma.
hepatitis, chronicInflammation of the
liverpersisting for a prolonged period.
Eventually, scar tissue forms and liver
cirrhosismay develop.
Chronic hepatitis may develop follow-
ing an attack of acute hepatitis (see
hepatitis,acute). It may also occur as the
result of an autoimmune disorder, a viral
infection (see hepatitis, viral), a reaction
to certain types of drugs or, more rarely,
to a metabolic disorder, such as haemo-
chromatosisor Wilson’s disease.
Chronic hepatitis may cause slight
tiredness or no symptoms at all. It is
diagnosed by liver biopsy. Autoimmune
hepatitis is treated with corticosteroid
drugsand immunosuppressants. Viral
infections often respond to interferon.
In the drug-induced type, withdrawal of
the medication can lead to recovery. For
metabolic disturbances, treatment de-
pends on the underlying disorder.
hepatitis D An infection of the liver
caused by the hepatitis D virus, which
occurs only in people who already have
hepatitis Binfection. People who develop
hepatitis D will usually suffer from
severe chronic liver disease.
hepatitis E A type of hepatitis, caused
by the hepatitis E virus, transmitted in
contaminated food or drink. The dis-
ease is similar to hepatitis A.
hepatitis, viralAny type of hepatitis
caused by a viral infection. Five viruses
that attack the liver as their primary tar-
get have been identified. They cause
hepatitis A,hepatitis B,hepatitis C,hep-
atitis D, and hepatitis E.
hepatomaA type of liver cancer.
hepatomegalyEnlargement of the liver,
occurring as a result of any liver disor-
der (see liver, disorders of).
herbal medicineSystems of medical
treatment in which various parts of
different plants are used to promote
health and to treat symptoms.
hereditary spherocytosisSee sphe-
rocytosis, hereditary.
heredityThe transmission of traits and
disorders through genetic mechanisms.
Each individual inherits a combination of
genesvia the sperm and egg cells from
which he or she is derived. The interac-
tion of the genes determines inherited
characteristics, including, in some cases,
disorders or susceptibility to disorders.
(See also genetic disorders; inheritance.)
heritabilityA measure of the extent to
which a disease or disorder is the result
of inherited factors, as opposed to envi-
ronmental influences such as diet and
climate. Certain disorders (such as hae-
mophiliaor cystic fibrosis) are known to
be caused entirely by hereditary factors.
Others are caused by environmental
factors. Between these extremes are
many disorders (such as schizophrenia)HEPATITIS B HERITABILITY
H