Hepatitis B
Hepatitis B is one of the major diseases of mankind and is a serious global public health
problem .It is caused by hepatitis B virus (HBV). HBV has a diameter of 42nm. It is a
double-shelled deoxyribonucleic acid virus of the class Hepadnaviridae .The outer surface
membrane contains hepatitis B surface antigen (HBsAg), which also circulates in blood as
22-nm spherical and tubular particles. The inner core of the virus contains hepatitis B core
antigen (HBcAg), hepatitis Be antigen (HBeAg), a single molecule of partially doublestranded DNA, and DNA-dependent DNA polymerase.
How HBV infect the liver
Most damage from hepatitis B virus is caused by the body's response to the infection. The
body's immune response against the infected liver cells (hepatocytes) damages the cells,
causing liver inflammation (hepatitis). As a result, liver enzymes (transaminases) leak out
of the liver into the blood, causing transaminase blood levels to be elevated. The virus
impairs the liver's ability to produce the clotting factor prothrombin, increasing the time
required for blood clot formation (prothrombin time).
Liver damage also impairs the body's ability to rid itself of bilirubin (a breakdown product
of old red blood cells), causing jaundice (yellow discoloration of the eyes and body) and
dark urine.
Transmission
HBV is present in the body fluid of the patient mainly in blood, semen and vaginal
secretion .It is also present in the milk, saliva, urine and tear in trace quantity and usually
not infectious.
Hepatitis B spreads by contact with an infected person's blood, semen, or other body fluid.
Getting hepatitis B by having sex with an infected person without using condom.
Also sharing and using injecting, contaminated and personal instruments, like drug needles
and toothbrush, can transmit HBV.
An infected woman can give hepatitis B to her baby or through her breast milk.
Blood transfusion can also be the way to transmit HBV. However, the Red Cross has been
screening all blood samples for HBsAg since 1978 to ensure the quality of blood.
Do not get hepatitis B by shaking hands, hanging and sitting next to an infected person.
Disease and consequence
Hepatitis B virus cause acute and chronic hepatitis.
The signs and symptoms may include jaundice, fatigue, abdominal pain, loss of appetite,
nausea, vomiting, joint pain and dark yellow urine.
The incubation period (to the onset of symptoms) varies usually between 45 and 120 days,
with an average of 60 to 90 days. The variation is related to the amount of virus in the
inoculums, the mode of transmission and host factors.
A short infection, which most people become infected with hepatitis B can get rid of the
virus within 6 months, is now known as "acute" case of hepatitis B.
Generally, during acute hepatitis, there is an increase in serum transaminase
(aminotransferase) activity, especially ALT (alanine aminotransferase, an enzyme that
interconverts L-alanine and D-alanine. It is a highly sensitive indicator of hepatocellular
damage. When such damage occurs, ALT is released from the liver cells into the
bloodstream, resulting in abnormally high serum levels), and AST (aspartate
aminotransferase, the enzyme that catalyzes the reaction of aspartate with 2-oxoglutarate
to give glutamate and oxaloacetate. Its concentration in blood may be raised in liver and
heart diseases that are associated with damage to those tissues) activities. They are
increased to a level which ranging from 10 to 50 times above the upper limit of the normal
range.
Also, jaundice usually becomes apparent clinically during acute hepatitis, as bilirubin level
is generally high during acute infection. (Jaundice becomes apparent clinically when the
total bilirubin level exceeds 20 to 40 mg/l)
Normally, the serum transaminase activity and bilirubin level during acute hepatitis are
higher than that during chronic hepatitis. After several months, about 90%to 95% of
infected adults will develop antibodies against the disease and get rid of the virus.
The risk of becoming chronically infected depends on the age at the time of infection.
Many chronic carriers do not have any symptoms although hepatitis B virus is still in their
bodies. They will never develop antibodies to the virus.
About 5-10 percent of adults who are infected with HBV will develop chronic hepatitis B.
Over 90% of infected neonates and 50% of infected young children will become
chronically infected.
Chronic carriers will usually have on going inflammation of the liver and may eventually
develop cirrhosis and liver cancer. Fortunately, there are also some healthy carriers will
never develop complications.
Only a small numbers, about one percent, develop life-threatening acute fulminant
hepatitis from the virus. They can be fatal if not treated immediately.
Prevention
To prevent infecting HBV, people should observe personal hygiene, for example, they
should wear glove to handle blood and body fluids contaminated area and instruments, and
should not share personal, injecting and contaminated instruments like razor, toothbrush,
drug needles or nail-cutter. They should also avoid unprotected sex.
The most effective way to prevent HBV is injecting HBV vaccine. HBV vaccine contains
HBsAg, which is injected into the human body to stimulate the production of protective
antibody against HBV infection. The full course is composed of three dose injected
separately in 0,1st,and 6th month. About 90-95% of recipients can produce long-term
immunity. The vaccine is only useful to those people who have no past exposure to HBV.
Diagnosis
To test for HBV, liver biopsy and blood test are available.
Having blood test, people can know whether or not having antigens of HBV and
antibodies against HBV.
Anti-HBs +: Indicates individual has been vaccinated, has received immune
globulin, is immune, or is an infant who has received antibodies from its
mother.
Anti-HBc +: Indicates past or present infection and lasts indefinitely. Also
may be detected in someone who has received immune
globulin or an infant who has received antibodies from its
IgM anti-HBc +: Indicates recent infection with HBV, usually within 4-6 months.
HBeAg +: Indicates active viral replication and high infectivity.
HBsAg +: Indicates acute or chronic HBV. Persistence for 6 months after
acute infection indicates progression to chronic HBV
Liver biopsy is a simple test .The doctor removes a tiny piece of your liver through a
needle .The doctor checks the piece of liver for signs of hepatitis B and liver damage.
Treatment
There are no specific treatments for acute hepatitis B. Infected person may rest, be
abstinent from alcohol, and avoid liver toxic drug.
However, there are two approved treatments for chronic hepatitis B -interferon alfa -2b
and lamivudine. Only patient with active HBV replication are suitable. Both drugs should
not be given together.
Interferon alfa-2b acts to inhibit viral replication and enhance the activity of the host
immune system. Interferon alfa-2b is injected below the skin three times a week for 4
months. However, it has many side effects including flu-like symptoms, fatigue, headache,
nausea and vomiting, loss of appetite, depression and hair thinning.
Overseas studies show that about 10% of the patients receiving treatment can eliminate the
virus successfully.
Since interferon may depress the bone marrow, blood tests are needed to monitor white
blood cells, platelets.
Lamivudine is to suppress the replication of virus DNA. It is taken orally once daily. It is
given for at least one year, may be somewhat lower. Comparing with interferon alfa-2b, it
has less side -effects. It is very well tolerated but viral resistance to treatment may occur.
If hepatitis B virus damage your liver seriously, liver transplant is necessary.
Epidemidogy
It is estimated that 350 million of people are carriers of HBV in the world. Three
quarters of them are Asian. Male to female ratio is 6 to 1.
In Hong Kong, the HBV carrier rate has been declining to 8-10% in the past 20 years.
About 40% of the adults have been infected with HBV.
Infection is less common in Western Europe and North America, where less than 1% is
chronically infected.
Highly endemic area is in Africa and Far East, where 10%-15% carry HBV.
The countries, which are highly endemic, may be because of their poverty. The
government cannot afford the money paying for hepatitis B vaccine, as the vaccine is so
expensive. Therefore, they infect HBV more easily. Another reason may be they do not
know hepatitis B well. They do not know how will transmit HBV and prevent it. Also,
they may not attach importance to hygiene, for example, they may be contact with blood
without wearing glove.
Therefore, if wanting to reduce the rate of hepatitis B carrier of these countries, publicity
of hepatitis B is needed. The government in these areas must publicize hepatitis B and tell
people how to prevent it. Also, the government must tell people attach importance to
hygiene, especially, they must avoid contact directly with blood and unprotected sex .In
these highly endemic areas, hepatitis B vaccine must be used. Because of their financial
problem, some organizations can help them, for example, Global Alliance for Vaccines
and Immunization and the Global Fund for Children's Vaccines.