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HEPATITIS B VIRUS (HBV)

HEPATITIS B VIRUS (HBV)

HBV causes serum hepatitis. It is a DNA virus classified as a “Hepadna” virus. There morphologic forms are known.

1- 22nm spherical particles. These are the commonest.

2- 22nm tubular particles that are over 200 nm long.

The two are made up of hepatitis B surface antigen (HB_sAg)

3- A large 42 nm spherical pratical ( dane partical).

These are the complete virions of HBV and consist of an outer envelope (HBsAg) which surrounds an inner core of nucleocapsid protein( HBcAg) which surrounded the viral DNA and DNA Polymerase. (HBeAg) is also apart of the inner core.

• mode of transmission :
  1. parenteral by blood and plasma transfusion   or by the prick of contaminated needles. Risk groups include, drug abusers, medical  personnel , renal dialysis patients and those receiving transfusion repeatedly.
  2. sexual contact as the virus is found in semen and vaginal secretion.
  3. perinatal transmission from mothers with hepatitis B to the new born during birth or breast feeding

*pathogenesis :

After enteing the blood , the virus infects hepatocytes causing necrosis and inflammation. Immune attack against viral antigens an infected  hepatocytes is  mediated by cytotoxic T cell casing hepatocellular cell mediated tissue injury .this is most probably the main cause of damage , since HBV does not cause acytopathic effect. The chronic sequelae are most probably due to autoimmune reactions to liver membrane antigens induced by the virus.

• clinical findings  and outcome of infection :

many of HBV infection  are asymptomatic and are detected only by the presence of antibodies to HBsAg. After exposure there is along incubation period 2-6 months which is much longer than that of Hepatitis A. The symptoms are more severe in hepatitis B than in HAV. And can lead to life threatening complication. Unlike hepatitis A. about 10% of hepatitis B patient become chronic carriers with persistent HBV antigenaemia, which is due to persistent infection of hepatocytes.

The virus is present in the blood and other body fluids e.g. semen, saliva, vaginal secretions and milk. Most carriers active hepatitis , which can lead to cirrhosis, fulminate hepatitis and death.

A high rate of hepatocellular carcinoma (HCC) ,occurs in chronic carriers. During virus replication, it is found that some copies of viral DNA are intergratd into cell DNA which may explain the malignant predisposition  of such infection. recovery is associated with life long immunity mediated by antibodies to HBsAg.

*laboratory diagnosis :

1- increased level of liver enzymes.

2-detection of hepatitis markers i.e . antigens and antibodies in blood by ELISA.

* Antigens :

– HBsAg : is detected during the incubation period and during active disease ,it may remain for months  or years in carriers.

–HBcAg : is not detectable in serum. But can be found in the nuclei of liver cells .

–HBeAg : is present during the I.P., in the acute stage of the disease and in some chronic carriers. Its presence indicates that the serum contains high concentration of infective HBV and is highly contagious.

* Antibodies:

– HBs Ab: appears after disappearance of HBsAg and its presence indicates immunity.

– HBc Ab :appears with the onset of clinical disease and remains after recovery. It is also present in chronic disease.

-Anti – HBc IgM: detection confirms the diagnosis of recent infection.

There is a period of several weeks when HBs Ag has disappeared but HBsAb is not yet detectable. This is the window phase.

At this time, the HBcAb is always positive and can be used to make the diagnosis.

– HBe Ab: appears as HBe Ag disappears and it indicates recovery.

3- Detection of viral DNA by PCR.

4- Detection of viral DNA polymerase.

* Prophylaxis:

Pre – exposure prophylaxis by active vaccination of those at high risk. It is recommended for all newborns as part of their immunization schedule.

• plasma derived vaccine ( Hepta vax B ): This is prepares by purifying HBsAg from pooled plasma from healthy HBs Ag positive carries. The virus is inactivated. It is safe and effective in preventing HBV infection.
• Recombinant hepatitis B vaccine ( Recombivax ) is amore recent vaccine and has replaced the Heptavax B in several parts of the world. It contains HBsAg produced in yeast cells by the recombinant DNA technique. The vaccine is given in 3 intramuscular injections in the deltoid region at 1,2 and 6 months.

* Post – exposure prophylaxis: persons exposed by prick of contaminated needle or other wise or infants born to HBsAg positive mothers should immediately receive both hepatitis B specific immunoglobulin ( HBIG ) and hepatitis B vaccine, given simultaneously at different sites.

Other control measures include:

• proper choice of blood donor i.e. free of HBsAg.
• Use of plastic disposable syringes.

Treatment:  Alpha interferon is used in treatment of chronic hepatitis B.

HEPATITIS B VIRUS (HBV)

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