Viruses 1

Introdution virology

1. VIRUSES - Dr. ANKUR KUMAR

2. Characteristics of Viruses Obligate intracellular Possess either DNA or RNA but never both. Filterable - They are smaller than bacteria, passed trough bacterial filters. Can not be grown on artificial cell free media Multiply by a complex method, not by binary fission as seen in bacteria. Do not have a proper cellular organization. Do not have cell wall or cell membrane or cellular organelles including ribosomes . Lack enzymes necessary for protein and nucleic acid synthesis. Not susceptible to antibiotics.

3. MORPHOLOGY OF VIRUS

4. MORPHOLOGY OF VIRUS Viruses possess a Nucleic acid- DNA or RNA single or double stranded, circular or linear, segmented or unsegmented surrounded by a protein coat called ----- Capsid composed of polypeptides called- capsomeres Have antigenic property and specific for each virus Specific arrangement of capsomeres called- Symmetry Icosahedral (cubical) symmetry Helical symmetry Complex symmetry Nucleic acid & capsid together k/s Nucleocapsid

5. MORPHOLOGY OF VIRUS Some viruses also have an outer envelope surrounding the nucleocapsid Lipoprorein in nature ( Lipid+Protein ) Lipid part- derived from the host cell membrane P rotein part - virus coded, made up of peplomers , which project as spikes on the surface of the envelope- (e.g . Influenza viruses have hemagglutinin & neuraminidase peplomers ) Peplomers are antigenic, bind to specific receptors on the host cells. Most Viruses are Enveloped Except DNA viruses- P arvovirus , Adenovirus & P apovavirus RNA viruses- P icornavirus , Hepatitis A virus & H epatitis E virus .

6. MORPHOLOGY OF VIRUS Size of the Viruses E xtremely small, vary from 20-400 nm in size. Smallest- Parvovirus (20 nm) Largest- Poxvirus (400nm).

7. MORPHOLOGY OF VIRUS Shapes of the Viruses Most are roughly spherical, Except ----- Rabies virus: Bullet shaped Rotavirus- wheel shaped Coronavirus -petal shaped peplomers Ebolavirus : Filamentous shaped Poxvirus : Brick shaped Adenovirus : Space vehicle shaped Astrovirus -star shaped peplomers

8. VIRAL REPLICATION Attachment Penetration Uncoating Biosynthesis Assembly Maturation Release

9. 1 1

10. • VIRAL REPLICATION Viruses invade cells and use the host cell's machinery to synthesize more of their own macromolecules. • Once inside the host virus will either go into a 1. Lytic Cycle- destroying the host cell during reproduction. or • It will go into a 2. Lysogenic Cycle – a parasitic type of partnership with the cell

11. 1 Virus injects its DNA Virus DNA commands host cell to make new viral parts New viral parts assembled Cell lyses (breaks apart) and new viruses are released Virus attaches to host cell. LYTIC CYCLE

12. 1 2 LYSOGENIC CYCLE

13. 1 3 Does not begin immediately Viral DNA ( called a prophage) attaches to the host cell’s chromosomes – lies dormant. The virus DNA integrates with the host DNA and the host’s cell helps create more virus DNA . LYSOGENIC CYCLE

14. Morphological Changes in the Host Cells Damage to host cell chromosomes: - with HSV or adenovirus infection- Formation of chromatin rings surrounding the nuclear membrane in host cells. Formation of inclusion body- aggregates o f virions or viral proteins and other products of viral replication. characteristic of specific viral infections. demonstrated in virus infected cells under the light microscope. have distinct size, shape, location and staining properties to the host cell. lntracytoplasmic indusion bodies: Acidophilic, seen as pink structures when stained with Giemsa or eosin methylene blue stains (e.g. most pox.viruses and rabies lntranuclear inclusion bodies : basophilic in nature. Cowdry (1934) had classfied them into ----- Cowdry type A inclusions : They are variable in size and have granular appearance. Cowdry type B inclusions : They a re more circumscribed and multiple .

15. Inclusion body

16. LABORATORY DIAGNOSIS Direct Demonstration of Virus Electron microscopy lmmunoelectron microscopy Fluorescent microscopy Light microscopy Histopathological staining: To demonstrate inclusion bodies lmmunoperoxidase staining Detection of viral antigens ELISA, direct IF, ICT, flow through assays. Detection of the Specific Antibodies Conventional techniques- HAI, neutralization test and CFT. Newer diagnostic formats- ELISA, ICT, flow through assays. Molecular Methods to Detect Viral Genes Nucleic acid probe-for detection of DNA or RNA by hybridization PCR- for DNA detection by amplification RT-PCR- for RNA detection Real time PCR- for DNA quantification Real time RT-PCR- for RNA quantification Isolation of Virus by Animal inoculation Embryonated egg inoculation Tissue cultures: Organ c ulture , explant culture, cell line culture ( primar y, secondary and continuous cell lines).

17. Embryonated egg

18. Cell tropism o f human viruses

19. Bacteriophages Bacteriophages are viruses that infect bacteria Morphology of bacteriophage

20. Life cycle of bacteriophage Lytic cycle Lysogenic cycles

21. Bacteriophages Phages play an important role in the transmission of genetic information between bacteria by the process of transduction . They can carry antibiotic resistance genes or virulence genes. Bacteria can be typed by phage typing methods for epidemiological purposes

22. DNA VIRUSES

23. Herpesviruses capsid is icosahedral linear double-stranded DNA genome The envelope carries surface spikes

24. Classification of human herpesviruses

25. HERPES SIMPLEX VIRUS (HSV)

26. VARICELLA – ZOSTER Varicella = Chicken pox (Primary infection) Herpes zoster = Shingles (Reactivation of latent infection)

27. EPSTEIN - BARR VIRUS Causative agent of Heterophile (+) ve infectious mononucleosis Associated with : Nasopharyngeal Ca Burkitt's lymphoma Hodgkin's disease (mixed cellularity type) B cell lymphoma in patients with immunoficiency CNS lymphoma in AIDS patient Increase risk of Thymoma , tonsillar and gastric carcinoma.

28. HH V – 6 cause exanthem subitum / roseola infantum or sixth disease. HHV-8 is associated with AIDS / Non AIDS Kaposi sarcoma.

29. ADENOVIRUS Space vehicle (Hexagonal shape) shaped, non enveloped virus containing ds DNA.

30. Common syndromes associated with adenovirus infection

31. Poxviruses Large, being 250-300 nm by 300-350 nm in size, and just visible under a light microscope Genus Orthopoxvirus includes the viruses causing cowpox, vaccinia and variola The variola virus causes smallpox, eradicated now. Poxvirus causing molluscum contagiosum .

32. Long question Laboratory diagnosis of viral infections. Short notes ----- Replication of viruses Methods of detecting viral growth in cell cultures Inclusion bodies

33. MCQ 1. Which of the following viruses is/are enveloped? a . Poliovirus b . Adenovirus c . Herpesvirus d . Parvovirus 8 19 2. All of the following are RNA viruses except : a . Human adenoviruses b . Enterovirus c . Coxsackievirus d . Hepatitis A virus 3. All of the following viruses are transmitted by respiratory route except: a . Influenza virus b. Rotavirus c . Respiratory syncytial virus d. Rhinovirus

34. MCQ 4. All of the following are intracytoplasmIC inclusion bodies except a. Negri bodies b. Molluscum bodies c. Cowdry type A inclusions d. Guarnieri bodies 5. Which of the following vaccine is a killed vaccine ? a. Mumps vaccine b. Measles vaccine c. Rubella vaccine d. Semple vaccine

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