Hepatitis B Virus (HBV) - Morphology, Clinical features, Laboratory diagno..

HEPATITIS B VIRUS (HBV) – MORPHOLOGY, TRANSMISSION, CLINICAL FEATURES & LABORATORY DIAGNOSIS

INTRODUCTION TO HEPATITIS B VIRUS (HBV)

⇒ HBV was first observed in 1965 & named as Australia antigen. Later, in 1968, it was found to be associated with serum hepatitis & the name has been changed to Hepatitis B Virus (HBV).

⇒ HBV causes Type B hepatitis, the most widespread and the most important type of viral hepatitis.

⇒ HBV is the only hepatitis virus that contains DNA as genetic material.

MORPHOLOGY OF HEPATITIS B VIRUS (HBV)

 HBV is a complex 42 nm double-shelled particle consist of an outer envelope & an inner core.

⇒ HBV is assigned to a separate family Hepadnaviridae.

⇒ The outer surface or envelope of virus contains hepatitis B surface antigen (HBsAg).

⇒ The core of the virus consists of an icosahedral 27nm nucleocapsid, which contains Hepatitis B core antigen (HBcAg).

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⇒ Inside the core is the genome, a circular dsDNA & a DNA polymerase.

⇒ HBV, antigenically, have been divided into 3 types of particles as:-

  • HBsAg – Hepatitis B Surface Antigen a.k.a. Australia antigen.
  • HBcAg – Hepatitis B core Antigen a.k.a. Core antigen.
  • HBeAg – Hepatitis B early Antigen a.k.a. Early antigen.

TRANSMISSION ROUTE OF HEPATITIS B VIRUS (HBV)

⇒ HBV is a blood-borne virus and the infection is transmitted by Parenteral, Sexual & Perinatal route.

⇒ Parenteral Route – Blood, Saliva, Breast Milk, Semen, Vaginal Secretions, Urine, Bile & Feces.

⇒ Sexual Route – the risk increases with no. of partners & sexual relationships, HBV infection has occurred after artificial insemination- semen donor screening is obligatory.

⇒ Perinatal Route – Congenital or vertical transmission is quite common from carrier mothers. Infection is usually acquired during birth by contact of maternal blood with the skin & mucosa of the fetus.



RESISTANCE SHOWN BY HEPATITIS B VIRUS (HBV)

⇒ HBV is a relatively Heat Stable Virus than other hepatitis viruses.

⇒ Viable at room temperature for longer periods.

⇒ Heat at 60oC for 10 hours reduces infectivity by 100-1000 folds.

⇒ Exposure to hypochlorite or 2% glutaraldehyde inactivates infectivity but HBsAg may not be destroyed by such treatment.

CLINICAL FEATURES OF TYPE B HEPATITIS

⇒ The incubation period is long, about 1 – 6 months.

⇒ The clinical features HBV are similar to that of the HAV.

⇒ These include – Malaise, Anorexia, Nausea, Vomiting, hepatomegaly, splenomegaly & Jaundice.

⇒ In Severe cases – Liver cirrhosis, hepatocellular carcinoma & chronic hepatitis are common.

LABORATORY DIAGNOSIS OF HEPATITIS B VIRUS (HBV)

⇒ Lab diagnosis of HBV infection can be carried out by detection of Hepatitis B Antigens & antibodies which can be detected by sensitive tests like ELISA & RIA.

⇒ HBcAg is not detectable in the serum but can be demonstrated in liver cells by immunofluorescence.

⇒ The DNA levels of HBV can also be detected in serum by PCR.

PROPHYLAXIS OF HEPATITIS B VIRUS (HBV) INFECTION

⇒ General preventive measures include avoiding the use of unsterile needles, syringes & other materials, avoid risky promiscuous sex, Health education, screening for HBsAg & HBeAg in blood donors.

⇒ Immunization includes- Both active & passive immunization is available. Intramuscular administration of the Hepatitis B Immunoglobulin (HBIG) as soon as possible after any accidental exposure to HBV infection, three doses of Hepatitis B vaccine at 0, 1 & 6 months are administered intramuscularly provides immunity against HBV for many years.

TREATMENT OF HEPATITIS B VIRUS (HBV)

⇒ No specific antiviral treatment is available.

⇒ Interferon-alpha alone or in combination with other antiviral agents, e.g. famcyclovir, has been beneficial in some cases of chronic hepatitis.



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