Hepatitis B
Hepatitis B is an inflammation of the liver and is caused by the Hepatitis B virus (HBV), a
member of the Hepadnavirus family and one of hundreds of unrelated viral species which cause
viral hepatitis. It was originally known as "serum hepatitis" and has caused current epidemics in
parts of Asia and Africa. Hepatitis B is recognized as endemic in China and various other parts
of Asia. The proportion of the world's population currently infected with the virus is 3 to 6%,
but up to a third have been exposed. Symptoms of the acute illness caused by the virus include
liver inflammation, vomiting, jaundice, and rarely, death. Chronic hepatitis B may cause liver
cirrhosis which may then lead to liver cancer, a fatal disease with very poor response to current
chemotherapy.
Hepatitis B usually gets better on its own after a few months. It may, however, cause a more
serious chronic infection.
Structure
Virions consist of an outer lipid envelope and an icosahedral nucleocapsid core composed of
protein. The nucleocapsid encloses the viral DNA and a DNA polymerase that has reverse
transcriptase activity. The outer envelope contains embedded proteins which are involved in viral
binding of, and release into, susceptible cells. Virion shape is generally spherical with a
diameter of 40 - 48 nanometers (nm) but pleomorphic forms exist, including filamentous and
spherical bodies lacking a core. These "subviral" particles are not infectious.[citation needed]
The DNA genome is not segmented but rather partially double-stranded, containing a long and short
segment which overlap approximately 240 nucleotides to form an open circle. The longer strand is
3020-3320 nucleotides long, and the shorter is 1700-2800 nucleotides long. The virus can be
divided into four major serotypes (adr, adw, ayr, ayw) based on antigenic epitopes present on its
envelope proteins, and into eight genotypes (A-H) according to overall nucleotide sequence
variation of the genome. Different genotypes have distinct geographic distributions. For example,
genotypes B and C are prevalent in China and neighboring countries.
Transmission
Transmission results from exposure to infectious blood or body fluids containing blood. Possible
forms of transmission include (but are not limited to) unprotected sexual contact, blood
transfusions, re-use of contaminated needles and syringes, and vertical transmission from mother
to child during childbirth. Without intervention, a mother who is positive for the hepatitis B
surface antigen confers a 20% risk of passing the infection to her offspring at the time of
birth. This risk is as high as 90% if the mother is also positive for the hepatitis B e antigen.
HBV can also be transmitted between family members within households, possibly by contact of
nonintact skin or mucous membrane with secretions or saliva containing HBV.
The primary method of transmission reflects the prevalence of chronic HBV infection in a given
area. In low prevalence areas such as the continental United States and Western Europe, where
less than 2% of the population is chronically infected, injection drug abuse and unprotected sex
are the primary methods, although other factors may be important. In moderate prevalence areas,
which include Eastern Europe, Russia, and Japan, where 2-7% of the population is chronically
infected, the disease is predominantly spread among children. In high prevalence areas such as
China and South East Asia, transmission during childbirth is most common, although in other areas
of high endemicity such as Africa, transmission during childhood is also a significant factor.
The prevalence of chronic HBV infection in areas of high endemicity is at least 8%.
Roughly 16-40% of unimmunized[citation needed] sexual partners of individuals with hepatitis B
will be infected through sexual contact. The risk of transmission is closely related to the rate
of viral replication in the infected individual at the time of exposure.
Diagnosis
The original assays for detection of hepatitis B virus infection involve serum or blood tests
that detect either viral antigens (proteins produced by the virus) or antibodies produced by the
host. Interpretation of these assays is complex. The table below is organized chronologically,
from top to bottom:
Prevention
While abstinence is the only guaranteed way of preventing sexual transmission of hepatitis B.,
latex condoms, if used properly, greatly reduce the chances of transmission.
member of the Hepadnavirus family and one of hundreds of unrelated viral species which cause
viral hepatitis. It was originally known as "serum hepatitis" and has caused current epidemics in
parts of Asia and Africa. Hepatitis B is recognized as endemic in China and various other parts
of Asia. The proportion of the world's population currently infected with the virus is 3 to 6%,
but up to a third have been exposed. Symptoms of the acute illness caused by the virus include
liver inflammation, vomiting, jaundice, and rarely, death. Chronic hepatitis B may cause liver
cirrhosis which may then lead to liver cancer, a fatal disease with very poor response to current
chemotherapy.
Hepatitis B usually gets better on its own after a few months. It may, however, cause a more
serious chronic infection.
Structure
Virions consist of an outer lipid envelope and an icosahedral nucleocapsid core composed of
protein. The nucleocapsid encloses the viral DNA and a DNA polymerase that has reverse
transcriptase activity. The outer envelope contains embedded proteins which are involved in viral
binding of, and release into, susceptible cells. Virion shape is generally spherical with a
diameter of 40 - 48 nanometers (nm) but pleomorphic forms exist, including filamentous and
spherical bodies lacking a core. These "subviral" particles are not infectious.[citation needed]
The DNA genome is not segmented but rather partially double-stranded, containing a long and short
segment which overlap approximately 240 nucleotides to form an open circle. The longer strand is
3020-3320 nucleotides long, and the shorter is 1700-2800 nucleotides long. The virus can be
divided into four major serotypes (adr, adw, ayr, ayw) based on antigenic epitopes present on its
envelope proteins, and into eight genotypes (A-H) according to overall nucleotide sequence
variation of the genome. Different genotypes have distinct geographic distributions. For example,
genotypes B and C are prevalent in China and neighboring countries.
Transmission
Transmission results from exposure to infectious blood or body fluids containing blood. Possible
forms of transmission include (but are not limited to) unprotected sexual contact, blood
transfusions, re-use of contaminated needles and syringes, and vertical transmission from mother
to child during childbirth. Without intervention, a mother who is positive for the hepatitis B
surface antigen confers a 20% risk of passing the infection to her offspring at the time of
birth. This risk is as high as 90% if the mother is also positive for the hepatitis B e antigen.
HBV can also be transmitted between family members within households, possibly by contact of
nonintact skin or mucous membrane with secretions or saliva containing HBV.
The primary method of transmission reflects the prevalence of chronic HBV infection in a given
area. In low prevalence areas such as the continental United States and Western Europe, where
less than 2% of the population is chronically infected, injection drug abuse and unprotected sex
are the primary methods, although other factors may be important. In moderate prevalence areas,
which include Eastern Europe, Russia, and Japan, where 2-7% of the population is chronically
infected, the disease is predominantly spread among children. In high prevalence areas such as
China and South East Asia, transmission during childbirth is most common, although in other areas
of high endemicity such as Africa, transmission during childhood is also a significant factor.
The prevalence of chronic HBV infection in areas of high endemicity is at least 8%.
Roughly 16-40% of unimmunized[citation needed] sexual partners of individuals with hepatitis B
will be infected through sexual contact. The risk of transmission is closely related to the rate
of viral replication in the infected individual at the time of exposure.
Diagnosis
The original assays for detection of hepatitis B virus infection involve serum or blood tests
that detect either viral antigens (proteins produced by the virus) or antibodies produced by the
host. Interpretation of these assays is complex. The table below is organized chronologically,
from top to bottom:
Prevention
While abstinence is the only guaranteed way of preventing sexual transmission of hepatitis B.,
latex condoms, if used properly, greatly reduce the chances of transmission.
posted by healthedu @ 7:31 AM
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