HEPATITIS B :
This article describes about the following factors:
1. Introduction of Hepatitis B virus .
2. Types of Hepatitis B Virus .
3. Morphology , Diagnosis, prevention and treatment of Hepatitis B virus.
Introduction :
Hepatitis
B virus belongs to the family Hepadnaviridiae, under the genus ortho
hepadnavirus. It was discovered by Blumberg in 1965. It is a double
stranded DNA virus and is causing infection also called serum hepatitis since
HBsAg, the serological marker appearing first in the patient serum during
infection. It is highly contagious and causes chronic hepatitis, fulminant
hepatitis, cirrhosis of liver liver cancer and immune complex disease. However
in many cases symptoms are not found during the initial period, later the
patent develops the symptom like vomiting, yellowish skin, tiredness, dark
urine and abdominal pain. Hepatitis is a major global health problem.
Prevalence of hepatitis B has been high in sub- Saharan Africa and East Asia.
Moreover high rates of this chronic infection are found in amazon and the southern
parts of central Europe. An estimated one third of the global population has
been infected with HBV Approximately 350-400 million people have lifelong
chronic infection worldwide. According to world health organization, an
estimated 600,000 people die every year due to this related infection.
Morphology: It is known to be a small virus; however
an electron microscope study reveals that the virus exists in the three forms,
namely spherical form, tubular form and complete from (Dane particles).
Spherical form: It is very minute form
appearing with the size of 22nm in diameter. It is made up of HBsAg antigen.
Tubular form: It is also seen with
the size of 22nm in diameter and 200nm long.
Dane particles: This
particles was discovered by Dane in 1970. It is very large and its size
measures about 42nm in diameter. It is spherical in shape. It is composed of
outer envelope, inner nuclear capsid. The envelope carries Hepatitis B surface
antigen whereas nuclear capsid carries
core antigen (HBcAg) and partially double stranded DNA.
Envelope: Envelope is formed with 7nm thickness.
It contains proteins (Glycoproteins) are involved in viral binding and
penetration of virus into host.
Nuclear Capsid: The nuclear capsid
encloses the viral DNA and DNA polymerase but the enzyme action seems to be
compatible with the activity of reverse transcriptase enzyme of retroviruses.
It consists of core antigens (HBcAg).
Resistance character: it
is eradicated by chlorine and heat at 600c for one hour.
Viral
antigen:
Hepatitis B surface
antigen (HBsAg)
Hepatitis B core
antigen (HBcAg)
Hepatitis B precore
antigen (HBeAg)
Hepatitis
B surface antigen (HBsAg): It is otherwise called as Australia
antigen as it was observed from serum of an Australian aborigine. It includes four
subtypes adw, ayw, and ayr.
Hepatitis
B core antigen (HBcAg) :Usually it forms the intra cellular
core protein. It does not secrete and circulated in blood.
Hepatitis
B precore antigen (HBeAg) : It is a soluble antigen
circulating in blood.
Pathogenesis:
Sources:- Infected
person
Carrier (super carrier,
simple carrier)
Mode of
transmission:-
Feco oral transfer
Person to person
contact
Parentral route
Sexual transmission
Congenital transmission
Blood transfusion
Feco oral
transfer: Food
handlers are receiving the infection virus by this method.
Person to
person contact: Due to poor sanitation and over crowd,
the virus is being transmitted
From one person to
another person.
Parenteral
route: Virus can be
transmitted by using unsterile needles, syringes and the hospital untensils.
Sexual
transmission: Illegal sexual contact with infected
person enables them to be transmitted from one to another. It mainly acquires
through both homo sexual and hetero sexual.
Congenitial
transmission: The virus is
transmitted from infected mother to fetus through placenta.
Blood
transmission: Prior to transfer the blood into patient
blood should be completely examined since the blood carries the hepatitis
virus. Blood and blood products enable the virus to be multiplied in host.
High risk
group:-
Surgeons
Hospital personals
Sex workers
Drug addicts
Reservoir :- Human being
Human being
Pathogenesis : life cycle of virus
Virus enters through
blood stream and attached on the host liver cell. The capsid is allowed to be
penetrated into cytoplasm of host cell by means of endocytosis then it moves
towards the host nucleus through microtubule. Core particle of the virus is
dissolved and releases the tightly coiled DNA along with viral polymerase in to
host nucleus.in the host cell nucleus, partially double stranded DNA of HBV
converted into circular double stranded DNA with the help of host enzyme.
Circular double stranded DNA undergoes
transcription into HBV m- RNA and pregenomic RNA however; the largest m RNA is
taken for next level processing.
These mRNA is further
brought into cytoplasm of host cell. From mRNA, protein factor DNA polymerase
is synthesized. As a result, many structural proteins are formed especially
viral components; core protein and HBcAg7 are formed these structural proteins,
DNA polymerase get inside further into nucleus. Inside the nucleus, DNA
polymerase is attached on pregenomic m RNA. Thus m RNA acts as temple, DNA
polymerase especially attached on Steam loop region of m RNA and from
RNA, DNA is formed. This is called RNA DNA Hybird. Synthesizing of
positive DNA strand using polymerase occurs.
Synthesis of DNA from
RNA is called reverse transcription. Then the ds DNA become circularized and
gets packaged using viral components, and core protein thereby forming progeny
virus.
Next the virus will
exit from host cell through Endoplasmic reticulum and Golgi apparatus and
affect fresh cell.
Symptoms: Most
people do not experience any symptoms during the acute infection phase.
Symptoms include: Tiredness, Mild fever. Headache . Loss of appetite
Nausea stomach pain
Tan-colored bowel movements (stools) are the major symptoms. Moreover, Dark
urine Yellowish eyes and skin (jaundice) are another symptoms. Jaundice usually
appears only after other symptoms have started to go away.
Most people with
chronic hepatitis B have no symptoms.
Diagnosis: A
number of blood tests are available to diagnose and monitor people with
hepatitis B. they can be used to distinguish acute and chronic infections.
Laboratory diagnosis of hepatitis B infection focuses on the detection of the
hepatitis B surface antigen HBsAg.
World health
organization recommends that the people willing for blood donations must be
tested whether they have any previous infections of hepatitis B or not in order
to avoid the risk of infection caused by virus.
Lab
diagnosis:-
ELISA: detection of anti-hepatitis B
antibodies
PCR: viral DNA can be
detected.
Serology: Several
serological techniques are performed to detect hepatitis B antigen and
antibody. HBsAg is recognized to be associated with this infection. It is
detected in circulation within a month. The HBcAg is not detected in serum.
Treatment : There is no specific treatment for acute hepatitis
B. therefore, care is aimed at maintaining comfort and adequate nutritional
balance, including replacement of fluids lost from vomiting and diarrhea.
Chronic hepatitis B infection can be treated with drug, including oral
antiviral agents. Treatment can slow the progression of cirrhosis, reduce
incidence of liver cancer and improve long term survival.
Tenofavir or entecavir
are the drugs for oral treatment. The treatment does not cure hepatitis B
infection, but only suppresses the replication of the virus. therefore, it is
being prescribed.
Prevention : The hepatitis B vaccine is the mainstay of hepatitis
B prevention. World health organization recommends that all infants receive the
hepatitis B vaccine as soon as possible after birth, preferably within 24hours.
The birth dose should be followed by 2 or 3 doses to complete the primary
series.
Vaccination can be
recommended for Dialysis patients, recipients of solid organ transplantations
and blood recipients. People interned in prisons, drug abusers, people who have
sex with multiple sex partner and health care workers.
In order to avoid its
transmission through vaccination, injection practice should be safe.
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