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FUN FACT The 3 most valuable brand names on earth: Apple, Microsoft, and Coca-Cola. Virology DEFINITION – the study of viruses and virus-like agents. Structure Classification and evolution Methods of multiplication Diseases Techniques to isolate/culture Use in research and therapy Virology VIRUS (from the latin virus meaning toxin or poison) is a microscopic infectious agent that is an obligatory intracellular parasite. VIRUSES infect all types of organisms from animals and plants to bacteria Viruses lack organelles Virology AVIAN INFLUENZA Each virus contains a nucleic acid, capsid protein, enzymes, and sometimes a surrounding envelope. Each virus particle is the same size and does not grow or differentiate. Virus particles are seen under the electron microscope. VIROLOGY - Classification of Viruses Host range Very specific Enveloped or non-enveloped Type of nucleic acid in the virion (DNA or RNA) Shape ( symmetry of the viral capsid) Dimensions of the virion and capsid VIROLOGY - Viral Size 20 nm - 1000 nm VIROLOGY - Viral Structure VIROLOGY – NUCLEIC ACIDS RNA or DNA Double or singlestranded Segmented or nonsegmented ds DNA ss RNA non-segmented ss DNA ds RNA segmented VIROLOGY - Capsids Composed of protein subunits called capsomeres. Functions Protective nucleic acid Recognition/attachment to host cells Introduction of nucleic acid into host cell VIROLOGY - Envelopes Composition: lipids, proteins and glycoproteins Lipids from host cell membrane more pleomorphic and fragile than the capsid Easily lysed by detergents, disinfectants or damaged by the outside environment. Function Camouflage? Recognition/attachment to host cell Helps introduce nucleic acid into host cell Protects nucleic acid Viral Shape Helical (ex: rabies, ebola) PolyhedraI/icosohedral (ex: adenovirus, poliovirus) Viral Shape Complex (ex: bacteriophage) Animal RNA Viruses Retro: FeLV, FIV (lenti – slow) Paramyxo: Canine distemper, measles rinderpest Corona: FIP Rhabdo: Rabies Animal DNA viruses VIROLOGY – Multiplication of Animal Viruses Transmission: Attachment/Penetration: aerosols, break in skin, fluids (blood, saliva, sexual contact) bind to specific surface receptors Entry: fuse with or engulfed by the plasma membrane Release: lyse cells or bud through (plasma) membrane Several hundred in one cell during one replication cycle of several hours. Viral Life Cycle – 5 steps Entry into host cell Uncoating Replication of nucleic acids & production of proteins Maturation/assembly Release of virus Multiplication Cycle: Entry I 1. Entry – Engulfment (Endocytosis) Multiplication Cycle: Entry II 1. Entry (Fusion of cell membrane with viral envelope via spikes) Multiplication Cycle 2. Uncoating Nucleic acid is released from nucleocapsid VIROLOGY -Multiplication Cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Viral proteins 3. Replication of Nucleic Acids & Proteins A. DNA enters nucleus. B. DNA is transcribed. C. RNA is exported to cytoplasm & translated. D. DNA is replicated in nucleus. E. Viral DNA inserted into host genome. Cytoplasm Viral DNA A C Nuclear pore B Viral mRNA D Nucleus Replicated viral DNA E Mature virus Host DNA VIROLOGY -Multiplication Cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Viral proteins Cytoplasm Viral DNA Nuclear pore 4. Maturation/Assembly New nucleocapsids selfassemble Viral mRNA Nucleus 5 Replicated viral DNA Mature virus Host DNA Multiplication Cycle 5. Release of virus ATTACHMENT Click after each step to view process PENETRATION HOST FUNCTIONS UNCOATING Transcription Translation REPLICATION VIRAL LIFE CYCLE ASSEMBLY (MATURATION) RELEASE 23 MULTIPLICATION Transmission of Viruses Between Hosts ANIMAL VIRUSES AEROSOLS (airborne) OR INGESTION (water- or foodborne) FLUIDS (direct contact) PARENT TO OFFSPRING VECTORS MOST Picorna (FMD) Orthomyxo (Influenza) Corona (FIP) Reo FEW Hepadna Retro (FeLV, FIV) Herpes Papilloma FEW Retro Herpes Arena MANY Toga Flavi Bunya Rhabdo VIROLOGY - Outcomes of Animal Virus Infections Acute Infection Latent Infections Virus has a short duration and often not fatal, and disappears when the disease process ends. ( ex: parvovirus, measles in people) Virus can remain in equilibrium with the host and not actually produce disease for a long period, often many years. ( ex: human herpes simplex, Feline Herpes) Persistent/Chronic Infections Virus is often fatal and occurs gradually over a long period. ( ex: HIV/AIDS, FeLV, FIV (Feline immuodeficiency virus) Methods of diagnosis for viral diseases I. Serology ELISA Antibody titers Virus isolation II. Cytology or Histology Serology Look for viral antigens or anti-viral antibodies A four fold or greater rise in antibody titer between two serum specimens provides a positive diagnosis. Paired sera, the first taken as early as possible in the illness and the second 10 to 14 days after the onset of symptoms. Serology Methods ELISA (enzyme-linked immunosorbent assay) Most common test FeLV/FIV/Heartworm Histology and cytology Inclusion bodies - nuclear or cytoplasmic aggregates, usually proteins They usually represent sites of viral multiplication Negri bodies - a particular type of cytoplasmic inclusion VIROLOGY – INCLUSION BODIES A.Lung lesion in an African wild dog B. Inclusion bodies Negri bodies can be seen with a light microscope. A section through a Purkinje cell with Negri body in the cytoplasm Negri body PREVENTION Isolation of animals to keep them free from infection. Vaccination against likely infections. Notification of reportable diseases References http://www.pitt.edu/~super1/lecture/lec3331 /004.htm http://www.idexx.com/view/xhtml/en_us/s mallanimal/in-house-diagnostics.jsf