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Virus Transmission History Iwanowski (1892) Discovered viruses Beijerinck (1898) Demonstrated potency of viruses Walter Reed (1901) Twort & d’Herrelle (1915) Frosh & Loefller (1898) Foot & mouth disease Yellow fever Discovered bacteriophage Viral Size 10 nm - 500 nm Viral Structure Capsids Composed of protein subunits called capsomeres. Functions Protective Recognition/attachment to host cells Introduction of nucleic acid into host cell Envelopes Composition Lipids from host cell membrane Proteins Glycoproteins Function Camouflage? Recognition/attachment to host cell Genome RNA or DNA Double or singlestranded Segmented or nonsegmented ds DNA ss RNA nonsegmented ss DNA ds RNA segmented Viral Shape Helical Isometric (cubic) Viral Shape Complex Classification of Viruses Host range Very specific Enveloped or nonenveloped Type of nucleic acid Shape Bacteriophage Viruses that infect bacteria. Types of Bacteriophage Virulent Lytic multiplication cycle Temperate Lysogenic multiplication cycle E. coli host bacillus Bacteriophage Adsorption Lytic Cycle E. coli host bacillus Bacteriophage Bacterial Viral DNA DNA Penetration Adsorption Lytic Cycle E. coli host bacillus Bacteriophage Bacterial Viral DNA DNA Penetration Lytic phase Duplication of phage components; replication of virus genetic material Adsorption Lytic Cycle E. coli host bacillus Bacteriophage Bacterial Viral DNA DNA Adsorption Penetration Lytic phase Ec lip se ph as e Duplication of phage components; replication of virus genetic material Assembly of new virions Lytic Cycle E. coli host bacillus Bacteriophage Bacterial Viral DNA DNA Lytic Cycle Adsorption Penetration Lytic phase Ec lip se ph as e Duplication of phage components; Maturation replication of virus genetic material Assembly of new virions Lytic Cycle E. coli host bacillus Bacteriophage Release of viruses Bacterial Viral DNA DNA Adsorption Vi rio n ph as e Lysis of weakened cell Penetration Lytic phase Ec lip se ph as e Duplication of phage components; Maturation replication of virus genetic material Assembly of new virions Lysis Burst size http://www.oranim.ac.il/courses/microbiology/phagelab.htm Lytic Multiplication Cycle Lysogenic Cycle lysogen Lysogenic State Prophage Lysogenic Conversion Bacterium Disease Phage encoded property Corynebacterium diphtheriae Diphtheria Diphtheria toxin Clostridium botulinum Botulism Botulinum toxin Streptococcus pyogenes Scarlet fever Erythrogenic toxin Propagation of Bacteriophage Infect bacteria Mix with molten soft agar plaque Plate Determining φ Titer http://www.slic2.wsu.edu:82/hurlbert/micro101/pages/Chap9.html Animal Viruses Orfvirus Ebola virus Vaccinia virus Animal Viruses 3 orders (-virales) 21 families (-viridae) 14 RNA virus families 7 DNA virus families Families divided into genera (-virus) Multiplication Cycle of An Animal Virus 1. Attachment Glycoprotein spikes bind to receptors on host cell surface Attachment QuickTime™ and a Sorenson Video decompressor are needed to see this picture. Multiplication Cycle: Entry I 2. Entry (Endocytosis) Multiplication Cycle: Entry II 2. Entry (Fusion of cell membrane with viral envelope) Multiplication Cycle 3. Uncoating Nucleic acid is released from nucleocapsid Multiplication Cycle 4. Replication of Nucleic Acids & Proteins Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Viral proteins A. DNA enters nucleus. Cytoplasm Viral DNA A B. DNA is transcribed. C Nuclear pore B C. RNA is exported to cytoplasm & translated. Viral mRNA D Nucleus D. DNA is replicated in nucleus. Replicated viral DNA E. Viral DNA inserted into host genome. E Mature virus Host DNA Multiplication Cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Viral proteins Cytoplasm Viral DNA Nuclear pore 5. Maturation/Assembly New nucleocapsids self-assemble Viral mRNA Nucleus 5 Replicated viral DNA Mature virus Host DNA Multiplication Cycle 6. Release of virus Life Cycle of Retrovirus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Virus A. Penetration & uncoating of viral RNA. A (+) Viral RNA (+) B (+) B. Translation of + RNA. C. Synthesis of - RNA to serve as template for synthesis of new + RNA. D. Synthesis of + RNA. E. Assembly of new virus particles. (–) C Viral proteins D (+) (+) (+) (+) E Capsid Cytoplasm Nucleus Damage to Host Cytopathic effects Syncytia Inclusion bodies Outcomes of Animal Virus Infections Acute Infection Persistent Infection Late complications following an acute infection Latent infection Chronic infection Slow infection Cell Transformation Acute Infections Short duration Host normally develops long-lasting immunity Nester et al (2007) Microbiology: A Human Perspective, 5th ed., McGraw-Hill, New York, NY, p. 342 Persistent Infections Nester et al (2007) Microbiology: A Human Perspective, 5th ed., McGraw-Hill, New York, NY, p. 348 Persistent Infections Nester et al (2007) Microbiology: A Human Perspective, 5th ed., McGraw-Hill, New York, NY, p. 348 Transformation of Host Cells Viral Host Range Usually very narrow Can be broadened Phenotypic mixing Genetic Reassortment Phenotypic Mixing Viruses switch protein coats. Genetic Reassortment Occurs in viruses with segmented genomes. Leads to antigenic shift. Propagation of Animal Viruses Must have living cells Cell/tissue culture Embryonated chicken eggs Live animals Cell/Tissue Culture Primary culture Tissue prepared directly from animal. “normal” cells Tumor cell lines Immortal cell lines Embryonated Chicken Eggs Signs of viral propagation Death of embryo Pocks on membranes Quantitation of Animal Viruses Nester et al (2007) Microbiology: A Human Perspective, 5th ed., McGraw-Hill, New York, NY, p. 357 Plaque assay Microscopic assay ID50 or LD50 assay Dilution at which 50% of inoculated host cells are infected or killed. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Hemagglutination assay http://homepage.usask.ca/~vim458/virology/stud2006/k9flu/ hemagglutination_assay.jpg + hemagglutination - hemagglutination Useful for titering flu virus Plant Viruses Wheat mosaic virus Tobacco mosaic virus Spread of Plant Viruses Enter via wound or insect bite. Spread from cell to cell through plasmodesmata. Copyright © Mayang Murni Adnin, 2001-2005. Prions Discovered by Stanly Prusiner in 1982 1997 Nobel Prize in Medicine Infectious proteins that attack animals. Causes transmissible spongiform encephalopathies (TSE). Spongiform Encephalopathies Humans Sheep QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Scrapie Cows Kuru Creutzfeldt-Jakob Gerstmann-Sträussler Mad cow disease Deer and Elk Chronic wasting disease http://pathy.fujita-hu.ac.jp/~tsutsumi/photo/photo112-3.htm Viroids Infectious RNA that attacks plants. http://www.dpvweb.net/dpv/showfig.php?dpvno=362&figno=02 Catalyze hydrolysis of RNA. http://www.kcom.edu/faculty/chamberlain/Website/Lects/Prions.htm