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Animal Viruses Powerpoint
 

Animal Viruses Powerpoint

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    Animal Viruses Powerpoint Animal Viruses Powerpoint Presentation Transcript

    • Animal Viruses
    • Properties of Obligate Intracellular Parasites DNA or RNA, not usually both DNA/RNA DNA/RNA Nucleic acids in mature particle Host cell synthesis Fission Fission Mode of replication - + + Antibiotic susceptibility Variable + + Rigid cell envelope - + + Independent protein synthesis - - + Generation of metabolic energy Viruses Chlamydiae Rickettsiae Property
    • Definitions of Terms for Viruses and Viral Infections
      • Virion – mature infectious virus particle
      • Capsid – protein shell that encloses and protects the viral nucleic acid
      • Capsomer – polymers of polypeptide chains which are the morphological units of icosahedral capsids
      • Core – internal part of a virus partciel, which consists of the nucleic acid and closely associated proteins
      • Nucleocapsid – structure composed of the capsid containing the nucleic acid or core
    • Definitions continued
      • Envelope – viral membrane, consisting of a lipid bilayer, proteins and glycoproteins
      • Peplomers (spike proteins)– viral proteins or glycoproteins that project from the envolope
    • Definitions continued
      • +ssRNA – single stranded RNA of the same polarity as messenger RNA
      • -ssRNA – single stranded RNA complementary to messenger RNA
      • vRNA – RNA of an intact ssRNA virus particle
      • cRNA – RNA that is complementary to the RNA of an intact ssRNA virus particle
      • cDNA – complementary DNA made from a viral RNA by recombinant procedures
    • Definitions continued
      • DNA dependent DNA polymerase (DNA polymerase) – an enzyme that uses DNA as a template for producing DNA
      • DNA dependent RNA polymerase (RNA polymerase) – an enzyme that uses DNA as a template for producing RNA
      • RNA dependent RNA polymerase (reverse transcriptase) – an enzyme that uses RNA as a template for producing DNA
    • Definitions continued
      • Transfection – in infection of mammalian or bacterial cells by vare viral nucleic acid
      • Transformation – stable hereitable change in the genetic makeup and phenotype of a cell resulting from the infection of that cell by a virus
      • Permissive cells – cells that support the complete virus life cycle, with production of infectious virus particles
    • Definitions continued:
      • Nonpermissive cells – cell which permit only part of the virus life cycle, usually transformed by viruses, especially DNA viruses
      • Productive infection – infection that results in th eproduction of infectious virus
      • Nonproductive infection – infection that has no infectious virus, cells may be transformed
      • Defective virus – virus that is not capable of going through its entire replicative cycle unless the cell is infected with a complete virus particle as well.
      • Cytopathic effect – observable damage to a cell resulting from virus infection
    • Structure of Animal Viruses
      • Size – not seen under the microscope
      • Nucleic Acid – varies
        • 12 codons -numerous codons
        • Segmented genomes
        • Either DNA or RNA, not both
      • Capside
        • Capsomeres protect nucleic acid
      • Baltimore’s Classification
        • Class I – ds DNA
        • Class II – ss DNA
        • Class III – ds RNA
        • Class IV – ss+ RNA
        • Class V – ss- RNA
        • Class VI – RNA tumor viruses (retroviruses)
    • Baltimore’s Classification System
        • Class I – ds DNA
        • Class II – ss DNA
        • Class III – ds RNA
        • Class IV – ss+ RNA
        • Class V – ss- RNA
        • Class VI – RNA tumor viruses (retroviruses)
      • Capside
        • Capsomeres protect nucleic acid
          • Complex – found in pox viruses
          • Isometric/Icosahedral
            • 20 facets with 12 vertices
            • Each hexomer has six neighbors
            • Number of capsomeres per capsid is used to classify icosahedral animal viruses
          • Helical
            • Naked helical viruses are all resistent
            • No naked human helical viruses
      • Viral envelopes
        • Surrounded by nucleocapsid
        • Formed by modified host cellular membrane
        • Contain host derived phosphlipid bilayer
        • Contains virus derived proteins and glycoproteins
          • Some are enzymes
          • Some provide attachment to cells
        • Envelopes are more fragile than naked viruses and are often inactivated by lipid solvents
    • Viral envelopes
      • Characteristics
        • Surrounded by nucleocapsid
        • Formed by modified host cellular membrane
        • Contain host derived phospholipid bilayer
        • Contains virus derived proteins and glycoproteins
          • Some are enzymes
          • Some provide attachment to cells
        • Envelopes are more fragile than naked viruses and are often inactivated by lipid solvents
          • Ether sensitive – have membranes
          • Ether resistent – have no membranes
    • Viral Proteins
      • Matrix proteins – M proteins
        • Found associated with the inner layer of the envelope, seem to make the envelope more rigid and help with organization of the virus particle
      • Fusion proteins – F proteins
        • Found on the envelope surface in some virus groups, cause viruses and virus-infected cells to fuse with uninfected cells
      • Nonstructural viral proteins
        • Enzymes found in the core of the virions of some virus types
    • Physiochemical Classification
      • 6 DNA and 13 RNA virus families, with one unclassified virus, classification is based on:
        • Chemical nature of the nucleic acid
        • Symmetry of the nucleocapsid
        • Presence or absence of the envelope
        • Number of capsomeres for isometric virions
        • Diameter of the nucleocapsids for helical viruses
      • Icosahedral viruses may be either DNA or RNA, enveloped or not
      • Helical viruses are all RNA, enveloped
    • Replication cycle, Productive Cycle
      • Attachment
      • Penetration
      • Uncoating
      • Transcription/translation of early mRNA
      • Replication of viral nucleic acid
      • Transcription/translation of late mRNA
      • Assembly of virions
      • Release
    • Replication cycle; Productive Infection
      • Attachment to specific receptor sites on the host cell membrane
        • Presence of specific receptor sites on the cell is the most important determinant of host specificity
        • Specie, tissue and physiological state of the cells determine the type of receptors present
        • Viruses tend to be host specific
    • Replication cycle; Productive Infection
      • Penetration by one of several methods:
        • Nonenveloped
          • Naked viruses may have rearrangement of the capsid protein after binding to cells, virus slips through by direct penetration of the membrane
          • Most are engulfed by receptor mediated endocytosis, with partial breakup of the capsid in the vacoule, followed by migration into the cyctplasm
        • Enveloped
          • Engulfement of virions by receptor mediated endocytosis via coated pits to coated vesicles which then fuse with lysosomes to form phagosomes
          • Fusion of the viral envelope and cell membrane, leaves the nucleocapsid inside the cell
    • Replication cycle; Productive Infection
      • Uncoating the viral nucleic acid
        • Attachment seems to lead to a conformation change in the capsid
        • Sometimes
          • cellular enzymes uncoat the viral nucleic acid
          • Synthesis of virus products may take place without completely uncoating the viral nucleic acid
    • Replication cycle; Productive Infection
      • Synthesis (Eclipse)
        • Use host cell enzymes in replcation
        • Synthesis of virus encoded macromolecules proceeds synthesis of:
          • early proteins
          • Viral genome proteins
          • Late proteins
        • Requires viral RNA and host machinery
    • Replication cycle; Productive Infection
      • Assembly
      • Release
        • Disintegration of infected cell (burst), especially for naked nucleocapsids
        • Slow release, with aquision of the envolope as the nucleocapsid buds through a virus-modified cellular membrane
        • Reverse phagocytosis
    • Mixed Virally Infected Cells
      • Mixed Viruses
        • Interference with replication of second virus
        • Complementation as some viruses are incomplete and can replicate only in the presence of another virus
      • Multiple Same Viruses
        • Recombination due to crossing over
        • Reassortment in viruses with segmented genomes
        • Reactivation can lead to rescue of a marker on an inactivated particle by superinfection of a live viris particle or virus particle inactivated by a different region
        • Interference at a large multpilicity of infection, may have defective particles produced
    • Cultivation of Viruses
      • Cell systems
        • Intact animals – very expensive
        • Embryonated egg
        • Tissue culture
          • Primary cell lines edrived directly from animals
          • Diploid cell strains from embryonic tissues, such as from a chick embryo can grow for 40-50 generations
          • Permament (cancerous) cell lines that may divide indefinately, such as Hela cells
    • Consequences of a Viral Infection
      • As seen in tissue culture
        • Cell death and lysis  CPE
        • Proliferation of host cell  masses of cells piled on each other
        • Fusion of membranes of adjacent cells leading to a multinucleate giant cell, thereby forming a syncytia
        • Transformation into malignant cancer cells
          • Viral nucleic acid integrated into host DNA
          • Viral nucleid acid arranged in circular duplex (similar to a nucleosome)
        • Silent infection (latency) with no morphologogical change in the cell
        • Steady-state persistent infection – infected cells produce and release virus
    • Measurement of Animal Viruses
      • Infectious units
      • Enumeration of total number of particles
      • Observation of viruses & products as antigens
      • DNA probes
      • PCR
    • Measurement of Animal Viruses
      • Infectious units
        • Plaque formation in tissue culture
        • Pock formation on chorioallantoic membrane in chick embryo
        • Focus formation if virus causes proliferation of cells
        • Serial dilution end point method
          • Cytopathic effects in tissue culture
          • Characteristic symptoms in experimental animals or eggs
      • Enumeration of total number of virus particles
        • Electron microscopy
        • hemagglutionation
    • Measurement of Animal Viruses
      • Observation of viruses and virus products as antigens
        • Complement fixation
        • Direct flourescent antibody
        • Gel immunodiffusion or immunoelectrophoresis
        • Radioimmunoassay
        • ELISA
    • Measurement of Animal Viruses
      • DNA Probes
        • Dot hybridization with autoradiography or ELISA readout
          • HPV 16,18 most common with cervical cancer
      • PCR gene amplification using small primer pairs of ssDNA
        • Nucleic Acid Amplification Testing (NAT) for calculation of viral load, such as HIV in blood
        • Other amplification methodologies, with HIV
    • Antibody Titer:Response to Animal Viruses
      • Types of tests
        • Neutralization of infectivity
        • Complement fixation
        • Hemagglutination-inhibition
        • Latex agglutination
        • Indirect ELISA
        • Indirect flourescent antibody
        • Radioimmunoassay
        • Western blot
    • Uses of Tests
      • Diagnosis
        • Need four-fold rise in titer
        • High concentrations on IgM
      • Surveys
      • Determine need for immunization
      • Lookback
    • Control of Virus Diseases
      • Prevention of transmission
        • Public health surveillance of the environment
        • Education
        • Isolation of cases of the disease
        • Passive immunization of contracts
        • Active immunization to creat an immune population
          • Vaccines may be either:
            • Live attentuated
            • Inactivated
            • Subunit vaccines
    • Live Attenuated vs Inactivated Vaccines No Rarely Reversion to Virulence No Occasionally Interference Poor Good Cell mediated response IgG only IgG, IgA Antibody response Usually less Many years Duration of Immunity Inactivated Attenuated Property
    • Treatment of Viral Disease
      • Symptomatic
      • Immune serum
      • Drugs
      • Interferons
        • Type 1 – α and β interferons
        • Type 2 – gamma interferons
    • Treatment of Viral Disease
      • Interferons
        • Type 1 – α and β interferons
          • Important cytokines for antiviral response
          • Synthesis induced by an infected cell with either a active or inactive virus, ds RNA or other compounds
          • Species – specific, not virus specific
          • Binds to recipient cell, activates a protein transcription factor
          • Have both a + and – effect on cells of the immune system, such as flu-like symptoms
            • α interferons used to treat hairy cell leukemia, Kaposi’s sarcoma, Hepatitis B, genital warts
            • β interferons used to treat multiple sclerosis
    • Treatment of Viral Disease
      • Interferons
        • Type 2 - gamma interferons
          • Important cytokines for antiviral response with activated T cells
            • gamma interferons used to treat chronic granulomatous disease
    • Patterns of Pathogenesis
      • Localized infections
      • Disseminated infections
      • Inapparent infections
      • Persistent infections
    • Patterns of Pathogenesis of Viral Infections
      • Localized infections – viral replication near site of entry
      • Disseminated Infections
        • local multiplication at site
        • extension through lymphatics
        • multiplication at second site
        • secondary viremia
        • Infectuon at target organ
    • Patterns of Pathogenesis of Viral Infections
      • Inapparent Infections
        • Very common, result from infection by attenuated virus
        • Considered to be very important since:
          • Represent an unrecognized source of dissemination of a virus
          • Confer immunity to the host
      • Persistent infections
        • Latent infections - Herpes
        • Chronic infections – Hepatitis B
    • Immunity to Virus Infectiuons
      • Interferons
      • Defective interference particle
      • Viral neutralization
      • Ig binding
      • Antibody complement mediated cylolysis
      • Antibody dependent cell mediated cytotoxicity
      • Lysis by natural killer cells
      • Cell mediated immunity
    • Immunity to Virus Infections
      • Interferons inhibit viral multiplication, temporary localized recurrences
      • Defective interference particles allow for temporary localized protection
      • Viral neutralization by antibody prevents viral infection from entering susceptable cells
      • Ig binding to virus can enhance defense host mechanisms by promoting phagocytosis
    • Immunity to Virus Infections
      • Antibody complement mediated cylolysis
      • Antibody dependent cell mediated cytotoxicity
      • Lysis by natural killer cells
      • Cell mediated immunity
        • Important for recovery from host viral infection, especially when host cells are not killed
    • Unusual immune reactions to viral diseases
      • Immunological tolerance
        • Examples of exposure in utero include:
          • Lymphocytic choriomeningitis (LCM)
          • Rubella
      • Diseases from virally-induced immunological response
        • Cell mediated response – hep B
        • Enhancing antibodies – flavovirus
        • Inactivated virus vaccine – respiratory syncytial virus
    • Dynamics of Parasitism
      • Transmissibilty
        • Mobility of the host, coupled with loss of virulence
        • Resistence to the effects of the parasite, so that the host lives long enough for viral transmission
        • Infects a variety of animals, although specific to species
        • If infect new species, tend to be more virulent
    • New virus diseases, zoonoses
      • Environmental changes increase human contact with vector
      • Genetic changes in virus
        • Point mutations
        • Intramolecular recombination
        • Genetic reassortment
    • How do we eliminate a virus from a population?
      • Limited antigenic types
      • Lifelong immunity
      • Limited subclinical cases
      • No carrier state
      • No animal reservoir
      • Good vaccine