Hepatitis B Virus Presentation PDF

HEPATITIS B VIRUS A Presentation By Dr R.Venkatajothi, MSc., MPhil, PhD, FIAAM, FAVRS Lecturer, Department of Microbiology MCS School of Medicine The Copperbelt University Date: 22-11-2024 ...

HEPATITIS B VIRUS A Presentation By Dr R.Venkatajothi, MSc., MPhil, PhD, FIAAM, FAVRS Lecturer, Department of Microbiology MCS School of Medicine The Copperbelt University Date: 22-11-2024  OBJECTIVES The objectives of this lecture are to  Discuss the morphology, classification, clinical features, laboratory diagnosis, treatment, prevention and control of Hepatitis B virus.  INTRODUCTION  Hepatitis B virus belongs to the Hepadnaviridae family.  The term ‘viral hepatitis’ is used to describe infections caused by a diverse group of hepatitis viruses. Viral hepatitis is a systemic disease that primarily infects the liver.  Six heterogeneous groups of viruses have been recognized, and named Hepatitis A, B, C, D, E and G.  Hepatitis B virus is a dsDNA virus and a species of the genus Orthohepadnavirus.  Hepatitis B Virus  Hepatitis B virus (HBV) is a widespread and important viral disease.  The Hepatitis B virus is mainly spread through sexual activity and contact with contaminated blood.  A high-risk group includes babies, young children and immunocompromised patients. Hepatitis B causes a more severe disease than hepatitis A. Asymptomatic HBV infections occur frequently.  Continued……  HBV causes serious liver diseases, including chronic hepatitis, cirrhosis and hepatocellular carcinoma.  Hepatocellular carcinoma is preventable by hepatitis B vaccine.  The epidemic of viral hepatitis B and C affects 325 million people globally and is 10 times larger than the global HIV epidemic. Every day, more than 3600 people die of viral hepatitis-related liver disease, liver failure and liver cancer.  Prevalence of HBV in Africa  Dying from viral hepatitis in Africa is becoming a bigger threat than dying from HIV/AIDS, malaria or tuberculosis.  In Africa, chronic viral hepatitis affects over 70 million Africans (60 million with hepatitis B and 10 million with hepatitis C).  Hepatitis B infection is preventable and treatable. The hepatitis C virus infection (HCV) is now curable.  Continued……  The availability of diagnostic tools and effective treatment, over 90% of people living with hepatitis B and C in Africa lack much-needed care.  The result is at least 200, 000 deaths a year in Africa, often among the adult population.  Morphology  The hepatitis B virus virion measures around 42 nm in size and contains a circular dsDNA genome.  It is also known as the “Dane particle.” The hepatitis B virus is an enveloped virus.  The virion encloses the viral genome and a DNA polymerase, all of which are surrounded by the hepatitis B core antigen (HBcAg) and an envelope containing the glycoprotein hepatitis B surface antigen (HBsAg).  Continued…… Morphology of Hepatitis B virus  Types of Hepatitis particles  An electronic microscope shows three types of particles in the sera of hepatitis B patients.  The most abundant form is spherical (20 nm in diameter).  The second type of particle is tubular, with a diameter of 20 nm and varying length.  These two types of particles represent the Australian antigen.  Continued……  The third type of particle, far fewer in number, is a double-walled spherical structure, 42 nm in diameter.  It was first described by Dane in 1970 and is also called Dane’s particle.  This Dane particle is the complete hepatitis B virus.  Continued…… Types of Hepatitis particles Dane particle  Antigenic structure of HBV  Antigens of HBV are: 1. HBsAg - surface antigen 2. HBcAg - core antigen 3. HBeAg - secreted protein  HBs Ag: It is a hepatitis B surface antigen occurring in 20 nm filamentous or tubular structures of varying length.  It’s found on the outer envelope of the Dane particle and is also called the Australia antigen.  Continued……  HBc Ag: The antigen expressed on the core is called the hepatitis B core antigen (HBcAg).  HBeAg: It’s a soluble, non-particulate nucleocapsid protein. It’s smaller than HBs Ag and exists in Dane’s particles in cryptic (invisible) form.  Pathogenesis  Mode of viral transmission:  Infection is transmitted through contaminated blood, blood transfusions, sexual intercourse, sharing of needles and razors, close personal contact, which occurs in families and body fluids such as saliva, breast milk, semen, vaginal excretions, and the carrier mother to her baby.  Continued……  Symptoms of Hepatitis B virus:  Hepatitis viruses produce acute inflammation of the liver, resulting in a clinical illness characterized by jaundice, headache, fever, joint pain, abdomen pain, gastrointestinal symptoms such as diarrhoea, nausea, and vomiting etc.,  Continued…… Symptoms of Hepatitis B virus  Continued……  HBV can cause acute or chronic, symptomatic or asymptomatic disease.  The most efficient way to acquire HBV is through injection of the virus into the bloodstream.  The virus replicates within hepatocytes.  The virus starts to replicate in the liver within 3 days of its entry.  Continued……  But the symptoms may not be observed for 45 days or longer.  It depends on the infectious dose, the route of infection, and the person’s immunity.  Sometimes HBV may not cause hapatitis, but may lead to the carrier state.  Infants & Immunodeficient people are more likely to become asymptomatic carriers following infections.  Continued……  Cell-mediated immunity is mainly responsible for causing the symptoms.  An insufficient T-lymphocyte cell response to the infection generally results in the occurrence of mild symptoms.  An inability of the T- cell response leads to the development of chronic hepatitis.  Antibodies can protect against initial infection by preventing the delivery of the virus to the liver.  Clinical features  The incubation period ranges from 2 to 5 months.  Primary virus replication takes place in the liver.  Virus particles and viral surface proteins are shed in the blood stream.  When a virus is present in the bloodstream, the condition is called viremia.  Continued……  Prolonged viremia can occur and the patient’s blood is highly infectious.  HBV causes inflammation of the liver (hepatitis), jaundice, severely damages the liver and leads to cirrhosis (chronic liver damage), hepatomegaly and hepatocellular carcinoma.  Hepatitis B carriers  A carrier form may be defined when there is persistence of the HBs antigen in circulation for more than 6 months. Carriers may be of the following types;  Super carriers: These are highly infectious, having a high titer of HBsAg, along with HBeAg, DNA polymerase and HBV, they remain present in the blood.  Hence, a very minute amount of serum or blood from carriers may transmit the infection.  Continued……  Simple carriers: Here, HBs antigen is found in the blood at a low titer. However, HBe antigen and DNA polymerase are absent in blood.  Transmission of infection is possible when large amounts of blood are transferred, e.g. during a blood transfusion.  By the way, simple carriers are more common.  Laboratory diagnosis  Specimen: Blood.  HBV does not grow in any conventional culture system.  The serological tests are immunodiffusion, counter immune electrophoresis, complement fixation, indirect hemagglutination inhibition, hemagglutination, radioimmunoassay and ELISA.  Continued……  Viral antigen detection:  Surface antigen (HBsAg) is secreted in excess into the blood. Its presence in the serum indicates that virus replication is occurring in the liver.  The HBs antigen can be identified by an ELISA test.  Core antigen (HBcAg), a core protein, is not found in the blood.  Continued……  ‘e’ antigen (HBeAg), a secreted protein, is shed in small amounts into the blood. Its presence in the serum indicates that a high level of viral replication is occurring in the liver.  Antibody response:  Surface antibodies (anti-HBs), ‘e’ antibodies (anti- HBe) and core IgM and core IgG antibodies are useful for the identification of HBV infections and carriers.  Continued……  These antibodies are identified by using ELISA and Immunochromotography test etc.  Molecular diagnosis: The PCR test is useful for virus isolation.  Treatment  No specific antiviral treatment is available for acute HBV infection. Interferon alpha, alone or in combination with other antiviral agents such as entecavir, tenofovir and famcyclovir has been beneficial in some cases of chronic hepatitis.  The hepatitis B vaccine gives protection against HBV.  The Hepatitis B vaccine is usually given in three doses for adults. It is also recommended that health care workers be vaccinated.  Prevention and Control  Prophylaxis of Hepatitis B Infections: Hepatitis B virus infection may be checked by observing the followings:  Screening of blood donors.  Use of sterile disposable syringes or needles.  Reduction in the number of sexual partners.  Use of condoms.  Blood spills should be cleaned with 0.5% sodium hypochlorite.  Continued……  Vaccination is recommended for infants, children, and especially people in high-risk groups.  The vaccine must be given in a series of three injections, with the second and third given 2 and 6 months after the first.  Although no treatment is available for acute infection, hepatitis B immune globulin may be administered within a week of exposure and to newborn infants of HBsAg-positive mothers to prevent the disease.  LEARNING OUTCOMES At the end of the lecture, students should be able to: \  Discuss the morphology, classification, clinical features, laboratory diagnosis, treatment, prevention and control of Hepatitis B virus.  REFERENCE BOOKS  David Greenwood et al (2007), Medical Microbiology (7th edition). Churchill Livingstone Elsevier.  J. C. Pommerville (2004), Alcamo’s Fundamentals of Microbiology (7th Edition). Jones and Bartlett Publishers.  Mims et al, (2008) Medical Microbiology (4th Edition). Mosby Elsevier.  Patrick. R. Murray (2009), Medical Microbiology (6th Edition), Mosby Elsevier.