VIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptx

VIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptxVIROLOGY DPT.pptx

1. VIROLOGY Introduction And structure of virus

2. Virus Are smallest infectious agent containing only one kind of nucleic acid (DNA or RNA) as their genome, covered by a protective protein coat. Viruses are innert in extracellular environment,they replicate only in living cells. They can infect unicellular organisms like bacteria & algae and also higher plants and animals

3. Characteristic features of virus : Not cells Not capable of independent replication Can not synthesize own energy or own proteins (So can reproduce only within cells) Too small to be seen by light microscope Replicate in different manner ( i.e no binary fission or mitosis-one virus replicates to produce hundreds of progeny) Do not have nucleus cytoplasm mitochondria ribosomes

4. STRUCTURE OF VIRUSES Shapes - Variable spheres, rods, bullets or bricks Size range 20-300 nʍ

5. Four basic Components .Nucleic acid .Capsid .Viral proteins .Envelope (+/-)

6. Nucleic Acid (DNA or RNA): . Single stranded or double stranded . Classification

7. DNA viruses: Hepatitis B virus, Herpes simplex virus, Cytomegalovirus, Epstein-Barr virus Smallpox virus .RNA viruses: Polio virus, Hepatitis A virus, Rota virus Dengue virus, Hepatitis C virus, Rubella virus HIV, Measles virus, Mumps virus, Rabies virus, Hepatitis delta virus

8. Oncogenic viruses RNA tumor viruses Human T cell lymphotropic viruses cause leukemias and lymphomas Hepatitis C virus Causes hepatocellular carcinoma DNA tumor viruses Human papilloma virus causes benign warts which progress to malignant

9. Oncogenic viruses Epstein Barr virus causes Burkits lymphoma and Nasophayngeal carcinoma . Hepatitis B virus also causes Hepatocellular carcinoma

10. Viral Capsid: . A protein coat- Encloses nucleic acid . Made up of repeating subunits(Polypeptides) called capsomers .Nucleic acid + Capsid= Nucleocapsid .Capsid gives stability to virus particle as it is resistant to drying, heat, proteases etc.

11. .Capsid gives symmetry to virus particle .Icosahedral .Helical

12. Viral proteins: Capsid proteins Envelope proteins Enzyme proteins Matrix proteins

13. Viral Envelope: .Forms outermost covering for some viruses .Composed of host lipids and viral proteins .Surface proteins act as receptors .Confers instability to virus as it is sensitive to drying, heat and acids

14. Virus like agents Defective virus, Prions, viroids , pseudovirions Prions: Infectious particles composed of proteins only , lacking nucleic acid E.g. Creutzfeldt-jakob Defective virus: Nucleic acid + Proteins Can not repliicate without a Helper virus which provides its missing function E.g. HDV needs HBV

15. Classification of viruses Two major components of virus used in classification 1.Nucleic acid (DNA / RNA) 2. Capsid Size , symmetry, envelope present or not

16. Pathogenesis Changes at cellular level: Cell death Abnormal structures Inclusion bodies (Areas of viral proteins or viral particles E.g. Negri bodies-Rabies) Owls eye inclusions (CMV) Multinucleated giant cells by fusion of virus infected cells E.g Herpes virus infection

17. Malignant transformation Viral persistence may lead to malignant transformation E.g HCV, HPV etc No apparent change Virus persists but host cell continues to multiply and function

18. Clinical stages in the infected cell : .Virus transmission to host cell--- Skin, GIT, blood,respiratory tract etc. .Replication and cell damage---due to inhibition of cellular machinery .Immune response--- Cell mediated or antibody mediated .Persistence of infection--- can be true latency like HSV or persistence (virus continues to replicate and cause damage, also k/a chronic infection) like HIV, HBV

19. Factors responsible for persistence: .Antigenic variation .Immune tolerance .Down regulation of MHC class .Direct inhibition of mediators of immunity