Medical Virology For Dentistry Prof. Dr. Asem Shehabi Faculty of Medicine

1. i Medical Virology For Dentistry Prof. Dr. AsemShehabi Faculty of Medicine The Jordan University

2. Introduction • Virusesare electron-microscopic particles (size:10-300 nm) .. obligate intracellular.. Replicate only in Living host cells/Tissue culture ..Widely spread in Nature..About 100 Major human pathogenic groups • Viruses cause diseases in Human, Animals, Plants, Insects .. Transmitted by various routes. • VirusesGenome .. either single or double RNA / DNA.. Depending on the type of virus..It an be associated with Protein coat/Capsid or Envelop . • Most DNA viruses are double-stranded. • RNA virus with single positive stranded RNA . acts directly as m-RNA for transcript.. Negative stranded RNA first produces mRNA from the genome RNA.

3. Virus Morphology • Nucleocapsid: Genome surrounded by proteincoat / Capsid..Composed of numerous repeating similar subunits.. Capsomeres .. Each composed 1-3 polypeptides. • Capsid is the outer part of the virus.. Mostly contain spike-like structures.. called surface Glycoproteins.. act as receptor-binding protein attached to specific host cells..These surface Glycoproteins are like keys and Locks .. enter and exit the cell during infection. • Virion is Free viral infected particle..consisting of nucleocapsid or nucleocapsid plus Envelope. • Envelope:Glycoprotein +Lipid bilayer.. host cell membrane.. Protect virus in nature outside host cells.

4. Figure-1 Virus Structure

5. Virus Structure Components-1 • Viral Symmetry: Three main types.. Different sizes • Cubic / Icosahedral Symmetry.. Icosahedron has 20 equal lateral triangles, 30 faces.. HIV , Adenoviruses • Helical symmetry: Cylinder /Coil-like structure .. composed of single type capsomer ..Hollow tubes.. Tobacco plant virus . • Complex symmetry : No regular symmetry .. Poxvirus. • A virus’s genome includes up to 300 genes. • Few genes start to make all essential proteins for Virus structures.. virus production..using the host cells components to provide all necessary energy and metabolites for virus synthesis.

6. Icosahedral / Cupic - Helical SymmetryViruses

7. Main Structures of Viruses Cubic / Icosahedral & Helical Symmetry

8. Viriods & Prions • Viroids are the smallest known agents of infectious agents, circular, single-stranded molecules of infectious RNA.. Without a protein coat ..common as infectious virus in plants. • Prions are infectious protein particles causing transmissible and inherited neurodegenerative diseases (Transmissible Spongiform- Encephalo- pathy ) destroying CNS and causing brain damage ..Can be transmitted by eating contaminated animal meat with Prions . • Creutzfeldt-Jakob disease in humans , Scrapiein sheep and goats...Mad Cow Disease, 1986, England.

9. Virus Infection of Host-1 • Process of infection: Attachment.. Adsorption-Penetration.. Fusion / Endocytosis .. Uncoating.. Synthesis viral components.. Assembly and release by cell lysis or budding.. Death of infected cells. • Productive Infection: Virus successfully completes replication cycle and produces progeny virions..up to 100,000 new virus particles per infected host cell..Incubation period few hours-few days/weeks. • Abortive Infection: Virus enters the host-cell but cannot successfully complete replication.. This can result from a non-permissive host-cell/ immunity or because the virus is defective. - Abortive virus associated with Asymptomatic Infection.. can become persistent in host but without clinical symptoms.. Poliovirus.. Enteroviruses

10. Types of Viral Infection -2 • Latent Infection: Some viruses remain inactive within specific cell nucleus .. Virus-DNA/RNA.. Replicate later under certain conditions.. HSVs, HIV. • Human Virus pathogenesis: The vast majority of virus infections cause sub-clinical/ asymptomatic.. Few % are associated with clinical disease. • Pathogenesis of viruses : There are a number of critical stages during virus replication which determine the nature of the disease. • Site of entrycan influence the disease symptoms .. Respiratory tract, Skin , urinary tract.. etc. • Generally,Viruses shed from primary site of multiplication.. except from Central Nerve System

11. Virus-Host Reaction • Viruses have reactive sites on their surface in forms glycoproteins which interact with specific receptors on suitable host cells..form Binding sites. • The specificity of the reaction between viral protein and host receptor defines and limits the host species as well as the type of host cell that is infected. • Damage binding sites by disinfectants or heat or blocking by specific antibodies (neutralizing antibodies) converts viruses into non-infectious virions • Viruses Stability: Differ in their resistant to heat and disinfection according to their shell structure & composition.. Most viruses stable at 4 oC , pH 5-9 .. inactivated at 60 oC..100 oCkill most pathogenic viruses. Formaldehyde destroy infectivity but preserve genome..UV-light may kill naked DNA viruses

12. Virus Replication-1 1.Virus adsorption (direct attachment) or coat of enveloped viruses may fuse by presence F-protein with the host cell membrane and release the virus nucleocapsid into the host cytoplasm.. or by a process endocytosis which involves forming vesicle inside cell membrane & cell cytoplasm. 2. Uncoating : Refers to the release of the viral genome from its protective capsid to enable the nucleic acid to be transported within the cell, followed by transcription and translation 0f virus genetic code to form new progeny virions.

14. Virus Replication-2 3. Genome activation: In general, DNA viruses replicate mainly in the nucleus and RNA viruses mainly in the cytoplasm, but there are exceptions.. Pox DNA viruses replicate in the cytoplasm of the host cell. 4. Assembly: Viral nucleocapsids may enter the nucleus of infected cell ( Herpes virus, Adenovirus), Polio virus infect cytoplasm .. Accumulation of virions at sites of assembly may form Inclusions filled with viruses.. these are visible in stained infected cells . 5. Release: Formed virus particles by budding , cell lysis or disintegration.. Result in repeat infection cycles of new cells until developing body response

15. Virus Entry Into The Host-1 • Physical barriers: • Skin: Dead cells can’t support virus replication.. Most viruses which infect via the skin require Miner cuts or abrasions in the skin integrity..Humanpapiloma viruses & Herpesviruses.. Afew other viruses transmitted by insects.. ticks, mosquitos overcome the skin barrier, Example: Arboviruses cause Yellow fever , Hepatitis & Encephalitis • Respiratory tract: Viruses gain entry into mucosa Respiratory Tract by first binding to specific receptors on mucosal cells.. • All mucosal surfaces possess sophisticated immune defence mechanisms… IgA Antibodies.. Cell-mediated immunity..less important IgG, IgM

16. Virus Entry Into The Host-2 • Gastrointestinal tract : The low pH of gastric secretions inactivate most viruses.. Some viruses can survive.. gastric acid, bile salts.. Enteroviruses • Genitourinary tract : Relatively few viruses enter through mucosa of genital tract.. Cytomegalovirus, HBV, Herpesviruses • Conjunctiva : Many viruses infect eye mucosa.. Adenoviruses, Enteroviruses , Herpesviruses • Blood: All viruses reach bloodstream through other body sites or direct inoculation by Arthropod vectors, Blood transfusion: I.V route, surgery.. HBV, HCV, HIV, Cytomegalovirus and others.

17. Spread of Viral infection • Susceptible Host cells & Host Immune Response determine whether the infection will remain localized at the site of entry or cause systemic infection.. • Primary viraemia : Initial spread of virus into the blood stream directly or following spread from the first site of infection & multiplication ..Measles, Rubella. • Secondary viraemia: Occurs when primary viremia has resulted in infection of other organ tissues via bloodstream such as skin & later returned back to the blood stream. Example: Rabies virus ..Muscle tissues-Blood-Central Nerve System & return to blood.

18. Immune Responses to Viruses-1 • The immune response to viruses varies with the phase & route of the infection.. Divided into Specific and Non-specific defenses. • Viruses that infect via the Respiratory /GI tracts are exposed first to IgA, IgGand complement in the mucosal secretions. .First /second time viral infection • The virus must either attached or penetrate the Epithelial layer of the skin, Respiratory or GI tracts Mucosa to establish a clinical infection.. Later replicates in infected cells or spread to its target, tissue via the blood Viremic/lymph system phase. * Host try to stop virus dissemination by both the T-Cell mediated and Humoral responses.

19. Immune Responses to Viruses-2 • Presence of specific viral antibodies in the blood, tissue fluids, mucosa will allow them to bind to the viruses during subsequent infections .. inhibit their transit to their target cells.. Specific Antibodies bind to extracellular viral epitopes (surface antigenic determinant) • During the viremic phase antibodies and complements enhance opsonizing viruses by phagocytosis .. Prevent virus survive and replicate.. Some viruses are susceptible to direct lysis by complements. • Host immunodeficiency & Susceptibility to viral infection are always associated with decrease in level T cells response & specific antibodies production.

20. Interferons-1 • Interferons (IFNs) are the first lines of non-specific defense against pathogens because they are induced early after virus infection ..Before any other defense mechanisms appear .. They activate immune cells..Natural killing cells & Macrophages. • IFNs production amount vary from host to host & depending on the dose of virus and host response. • IFNs are cytokines.. specific glycoproteins which did not act directly on the virus, rather act on infected host cells to make them resistant to viral infection. • IFNs modify immune responses : Altering cell surface molecules by production & secretion of Antiviral Proteins.. These can inhibit many stages of Virus life cycle & some tumor cells .

21. Interferons-2 • Interferons are not specific against a particular virus • Three types of Interferons: • Alpha-IFN: Produced by blood mononuclear cells, epithelium.. 20 subtypes. • Beta- IFN: Produced by Fibroblasts cells • Gamma-IFN: Produced by T-Lymphocytes as natural killer cells in response to specific antigenic signal. • All IFNs help infected host cells functions to resist or recover from a viral infection & other invading organisms.

22. Growth of Viruses • Viruses can be detected in Laboratory by using: • Chick embryos, living animals, cell and tissue cultures. • Primary cell Lines/cultures are obtained directly from any normal organ.. Kidney, Liver. Semi-continuous cell lines can be subcultured up to 50 times.. Carry normal chromosomal count.. Epithelial-likecells.. • Continuous cell lines can be used indefinitely, originated from tumors or from normal cells which have become transformed during subculture.. have abnormal chromosomal count. • Cytopathic Effect (CPE) is observed when virus-induced cellular changes/ damages in tissue culture.

23. Cell Culture

24. Lab Diagnosis of viral infections-1 • Detection using cell culture: • The infective virus titer can be detected by counting plagues produced in cell monolayers • Cell culture changes include : lysis, swelling, rounding, transformation of cells, formation of multinucleated giant cells / Syncytia : Cytomegalovirus, Herpes. • Death of the cells: Measles &Mumps viruses • Production of cytoplasmic/ nuclear inclusions or both made visible by staining cell nucleus.. Herpes, Rabies. • Cytoplasm of the infected cell with viruses developed Basophilic or Eosinophilic inclusions .. Haemotoxylin -Eosin (H&E) staining is often used for staining tissues.

25. Diagnosis of viral infections-2 • Serological methods: Viral antigens/Antibodies can be detected by a wide range tests using polyclonal - monoclonal antibodies.. precipitation, agglutination, ELISA, immunofluorescence, complement fixation and radio immuno assays. • Molecular technology can diagnose rapidly most viral infections.. polymerase chain reaction (PCR).. amplify specific segments of viral nucleic acid.. Study virus Genotype & epidemiology of viral infection. • The ability to detect and sequence portions of a viral genome permits genetic markers of specific strains sub-strains to be identified.. Influenza virus. • Cell cultures are mostly used for vaccine production.

26. Vaccines • Live, attenuated vaccines contain a version of the living microbe that has been weakened in the lab so it can’t cause disease. • They induce strong cellular and antibody responses and often confer lifelong immunity with only one or two doses..immune competent persons. • Despite the advantages of viral live, attenuated vaccines, there are some problems: Viral mutation, Rarely cause actual clinical disease .. Side effects on CNS or other organs. • Most viral vaccines are more protective once given in children than adults.