HEPATITIS B :
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 centeral 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 (supper 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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