1. Introduction to Virology

1. Introduction to Virology - Virology Virology Properties...

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Unformatted text preview: Virology Virology Properties of viruses Structure of viruses Classification Viral Replication Epidemiology Transmission Viruses Properties: smallest known infective agents (prions?) (prions?) distinct from other organisms: small size - 10 to 300 nm (bacteria - 1000 to 7500 nm) genome - either RNA or DNA metabolically inert - no metabolic activity outside host cell; unable to replicate in inanimate media Properties of Viruses, Bacteria, Chlamydiae Property Size (nm) Obligate intracellular parasite Nucleic acids Bacterial-like cell wall Binary fission Ribosomes Sensitive to antibiotics Viruses 22 - 300 + 1 ----- Bacteria 300 - 3,000 -2 + + + + Chlamydiae 300 - 400 + 2 + + + + Viruses - Properties Virus-host cell interaction may result in: Virusi) ii) ii) cell death - due to cytopathic effect (CPE) of virus; also results in clinical disease cell transformation - cell converted to malignant or cancerous cell latent infection - persistent infection in quiescent state which may reactivate anytime to produce disease Viruses - Structure consist of a core of nucleic acid surrounded by a protein coat components of virus particle include: i) nucleic acid - DNA or RNA - single - or double - stranded - intact / fragmented; linear / circular Viruses - Structure ii) capsid - protein coat made of capsomeres iii) envelope - found in some viruses; lipoprotein envelope containing viral and host cell components Virion - intact virus particle Viruses - Structure Virus particles exhibit 3 types of capsid symmetry: i) helical - tubular: most helical viruses possess an outer envelope (eg. measles) (eg. ii) icosahedral - isometric or cubic; may (eg. (eg. herpes) or may not (eg. adenovirus) possess an (eg. outer envelope iii) complex - does not conform to either of above (eg. vaccinia) eg. vaccinia) Classification of Some Common Viruses Viruses - Classification Based on: i) type and structure of nucleic acid and strategy used for replication ii) type of capsid symmetry (helical vs icosahedral) icosahedral) iii) presence or absence of an envelope Family Picornaviridae Type of Viruses Nucleic Acid Enteroviruses, ss (+) RNA polio, hep. A Caliciviridae Norwalk virus ss (+) RNA Togaviridae Rubella ss (+) RNA Rhabodoviridae Rabies ss (+) RNA Paramyxoviridae Parainfluenza, ss (-) RNA RSV, measles, mumps Orthomyxoviridae Influenza ss (-) RNA Retroviridae HIV 1,2, HTL I,II ss (+) RNA Hepadnaviridae Hepatitis B ds DNA Parvoviridae Parovirus B - 19 ss (+) or (-) DNA Adenoviridae Adenovirus ds DNA Herpesviridae HSV, CMV, EBV, VZV, HHV6 ds DNA Envelope No No Yes Yes Yes Yes Yes Yes No No Yes Capsid Symmetry I I I H H H I Unknown I I I I = icosahedral, H = helical Viruses - Replication adsorption (attachment) entry uncoating transcription synthesis of virus components assembly release Virus Replication i) Adsorption (attachment): Results from a random collision with the cell Is mediated by an interaction between specific proteins on viral surface and specific receptors on target cell membrane not all cells carrying a receptor for a particular virus can be productively infected by that virus Virus Replication i) Adsorption (attachment): (cont'ed) (cont'ed) Some viruses may use more than one host cell receptor Some viruses are able to infect a limited spectrum of cell types (host range) Most neutralizing antibodies are specific for virion attachment proteins ii) Virus Replication Entry (penetration): 2 mechanisms - endocytosis (viropexis) viropexis) - fusion of virus envelope with cell membrane Uncoating: Uncoating: release of viral genome cell enzymes (lysosomes) strip off the virus protein (lysosomes) coat iii) Virus Replication iv) Transcription: production of virus mRNA or replicative intermediates from the viral genome involves host cell or virus - specified enzyme (polymerases) Virus Replication v) Synthesis of virus components: protein synthesis structural non-structural (enzyme for replication) non nucleic acid synthesis new virus genome most often by a virus - coded polymerase or replicase; with some DNA viruses a cell replicase; enzyme carries this out Virus Replication vi) Assembly: may take place in cell nucleus, cytoplasm or (with most enveloped viruses) at the plasma membrane Release: sudden rupture of cell gradual extrusion (budding) of enveloped viruses through the cell membrane may occur together with assembly Viruses - Epidemiology Factors that determine who gets a virus: mode of transmission age gender ethnic background / country of origin travel history occupation season underlying medical condition(s) vii) Viruses - Transmission - respiratory tract (inhalation or direct contact) - fecal - oral (ingestion) - sexual contact - inoculation through skin Vertical - mother to offspring (transplacental or (transplacental post - natal) Blood / blood products Arthropod vector Person to person Viruses - Transmission consider all body fluids / materials as potentially infectious (blood, urine, saliva, feces, tissue, etc.) use appropriate precautions to protect yourself and your patients handwashing disinfectants - the best are hypochlorite solution (which is corrosive) and gluteraldehyde; most viruses are gluteraldehyde; relatively resistant to phenols Always Remember! If its moist, and its not yours, don't touch it! ...
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This note was uploaded on 05/09/2010 for the course LMP 232 taught by Professor Crandall during the Spring '10 term at University of Toronto.

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