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158 Cards in this Set
- Front
- Back
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What are the main differences between viruses and other unicellular organisms?
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Viruses are no bigger than 300nm (some exceptions)
Do not grow on non-living media Do not undergo binary fusion Contain EITHER DNA or RNA Possess Infectious nucleic acids Do not possess ribosomes Do not maintain their own metabolism/have the mechanisms to do so Insensitive to antibiotics |
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What species do viroids and virusoids typically infect?
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Plants!
Only known mammalian viroid is heptatitis D in humans |
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What is the difference between viroids and virusoids in where they replicate?
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Viroids replicate in nucleus
Virusoids replicate in cytoplasm |
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What are the primary differences between viruses and prions?
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Prions do NOT contain nucleic acid
Prions do NOT induce an immune response Prions do NOT promote production of IFN Prions do NOT produce an inflammatory response |
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What are some modalities that can be used to visualize viruses?
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EM
Negative staining Computer enhanced imaging X-ray diffraction of crystals NMR |
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What are some examples of DNA virus families?
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Paroviridae
Papvaviridae Adenoviridae Herpesviridae Hepadnaviridae Poxviridae |
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What are some examples of RNA virus families?
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Togaviridae
Flaviviridae Picornaviridae Reoviridae Bunyaviridae Coronaviridae Paramyxoviridae Orthomyxoviridae Arenaviridae Rhabdoviridae Retroviridae |
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What are the most basic building blocks of viruses?
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Protein subunit
Structure unit Assembly unit Capsomer Capsid (coat/shell) Nucelocapsid |
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What structural differences are there between enveloped and non-enveloped viruses?
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Enveloped viruses possess: peplomer, spike, matrix proteins and lipids all associated with the viral envelope
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Where does the envelope come from for enveloped viruses?
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From host cell lipid bilyaer. Thus lipids and other components of viral envelope are IDENTICAL to host cell membrane
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What significance in there in the Spike or peplomer glycoproteins present on the nuclear envelope?
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Determine tissue topism
Determine virus attachment proficiency Determines host specificity |
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What is the characteristic epidemiology of enveloped viruses?
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Short survival
Labile (lipid molecules easy to destroy, & thus destroy viral attachment ability) Transfer of host/viral proteins Elimination of virus influences by envelope Typically cause seasonal diseases |
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What is the pathogenesis associated with most enveloped viruses?
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Reproduce via budding -> less lilely to destroy host cell
Typically cause chronic, persistent infections/diseases |
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What type of immunological response is/are typical in an enveloped virus?
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Glycoproteins associated with envelope act as immunologically "active" particles
Cell-mediated immunity Natural immunity Vaccine immunity |
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How does the lack of an envelop affect the characteristics of the non-enveloped viruses?
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Increases resistance -> Increased survival, greater chances for transmission, can produce disease year-round (NOT seasonal), more difficult to eliminate
Reproduction usually involves bursting cell Typically cause acute/less chronic disease |
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What types of structural proteins may be found in most viruses?
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Capsid/nucleocapsid
Envelope proteins = spike proteins, matrix proteins, etc. Ligands (VAPs) for cellular receptors |
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What are types of nonstructural proteins commonly found in viruses?
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Polymerases/transcriptases
Reverse transcriptases Integrases |
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What are the functions of the Structural proteins (specifically)?
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Capsid-types = protect genome
Envelope protein = protect virion particles & attachment Ligands = cellular attachment |
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What are the functions of the Non-structural proteins (specifically)?
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Polymerases = dsDNA/RNA converted to mRNA
Reverse transcriptases = Used in retroviruses to convert RNA to DNA Integrases = integrate proviral DNA of retroviruses into host genome |
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What is the chemical composition of most viruses?
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Nucleic acids
Proteins Carbohydrates -> Glycoproteins Lipids |
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What is a general pattern in the size difference between enveloped and non-enveloped viruses?
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Enveloped viruses are larger than non-enveloped. Typically.
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What 2 shapes do viral nucleocapsid most often take?
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Icosahedral/Cubical composed of 12 vertices, 30 edges and 20 triangles.
Helical. |
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All animal helical viruses are: enveloped or non-enveloped?
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Enveloped!
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How are viral genomes structured/organized?
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Single or Double Stranded
Monopartite or Multipartite (aka the genome is in 1 whole part or is in multiple parts) |
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What is the primary nucleocapsid structure for DNA viruses?
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Icosahedral
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For RNA viruses, what structure are the nucleocapsids for enveloped viruses?
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Helical
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How are glycoproteins incorporated into the viral membrane?
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Oligosaccharides are added to proteins in ER
Proteins move to Golgi complex then the cell membrane Viral membrane becomes part of the virus via budding |
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What function do viral glycoproteins have?
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Act as ligands for attachment
Function as enzymes Act as antigens for host immune cells |
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Match the suffix to the classification level:
Order -viridae Family -virales Genera -Strain Species -virus |
Order = -virales
Family = -viridae Genus = -virus Species = Strain |
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What types of structural, physio-chemical & genetic parameters are used to classify viruses?
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Virion properties = size, shape +/- envelope
Genome properties = DNA or RNA, strand, linear/circular Protein properties = Number, size, function Replication = transcription, translation, processing Physical properties = pH, cations, solvent, stability Biological properties = Antigenic relationship, host range, pathogenicity, tissue tropism |
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How are viruses categorized based on epidemiologic parameters?
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Based on clinical characteristics:
Enteric viruses Respiratory viruses Arboviruses Oncogenic viruses |
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What modalities are utilized to name viruses?
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Describe virus characteristics
Describe members of viral family Describe sites where virus was isolated Describe type of disease caused Describe places where virus was first found |
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Define Host Range
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Range of animals/tissues/cells that virus can infect (Host specificity)
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Define susceptibility
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Ability of host cells to become infected
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Define permissivity
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Ability to replicate and produce progeny viruses
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Define Portal of Entry
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Location of first infected cells
Usually not the site of disease signs |
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What are the types of infections that viruses produce?
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Productive
Abortive Restrictive Latent Recrudescent |
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What makes a viral infection productive?
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Results in production of infectious viral progeny
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What are the primary characteristics of an abortive viral infection?
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Replication was initiated but not completed
Limited gene expression Defective interfering viruses |
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What type of viral infection is characterized by transient permissivity with few virions released?
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Restrictive infection
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How are latent and recrudescent viral infections related?
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Latent infections are characterized by integration of the viral genome into the cellular genome without expression or production of viral progeny. Recrudescent infections are basically active latent infections where viral progeny are produced.
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What are the steps of viral replication?
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1. Attachment
2. Penetration 3. Uncoating 4. Transcription of early mRNA 5. Translation of early proteins 6. Replication of viral DNA 7. Transcription of late DNA 8. Translation of late proteins 9. Assembly of virions 10. Release of viral particles |
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What conditions are required for viral attachment?
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Complex but Rapid and Highly Specific process
No energy or temperature requirements for attachment HAHA Trick question! |
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What 3 methods of penetration are utilized by viruses?
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Translocation
Endocytosis Fusion |
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What are the major differences in methods of penetration between enveloped & non-enveloped viruses?
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Non-enveloped viruses typically use translocation
Enveloped viruses utilize endocytosis and fusion (some) |
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What viral replication process is essential for ALL viruses?
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Translation of viral mRNA to proteins
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Give some examples of structural proteins encoded for by viral mRNA.
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Capsid proteins
Envelope proteins Matrix proteins |
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What 3 main categories make up the non-structural proteins encoded for in viral mRNA?
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Viron-associated enzymes
Regulatory proteins Proteins influencing virulence, host range, topism, etc. |
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Proteins responsible for viral transcription, replication of viral nucleic acid and cleavage of other viral proteins all fall under what category of viral proteins?
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Non-structural, virion-associated enzymes
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What type of viral proteins control the temporal sequence of viral genome expression?
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Regulatory proteins
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Viral proteins influencing virulence, host range, tissue tropism, etc. are known as what?
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Virokines
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What are the ways in which virokines function?
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Modulate infection in an uninfected cell by:
Negating the effects of INF, TNF, etc. Reducing inflammatory response & complement activation |
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Oncogenic viruses would likely have a high concentration of what type of viral proteins?
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Non-structural regulatory proteins that up-regulate cellular genes.
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Match the process with the outcome:
Assembly Virions exit the cell Maturation Virions are produced Release Virions align with the cell membrane |
Assembly = Virions are produced
Maturation = Virions align with the cell membrane Release = Virions exit (are released) from the cell |
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What function doe the viral matrix proteins have in the assembly of a virion?
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Pull nucleocapsid toward the center of the membrane, helping to form a capsule within which the viral genome may be housed.
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What are 4 important characteristics of RNA virus replication?
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RNA is labile & transient (therefore it must be replicated quickly)
Most RNA viral genomes replicate in the CYTOPLASM RNA viruses must encode +ss RNA or carry an RNA Dependent RNA polymerase molecule with them in order to replicate in the host cell RNA viruses are prone to mutation due to the lack of proof-reading ability in RNA polymerase |
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What are the steps involved in +ss RNA viral genome replication?
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+ss RNA (basically the same as mRNA) enters cell cytoplasm
Ribosomes translate & synthesize viral proteins RNA polymerases produce (-)ss RNA = Stage 1 RNA polymerases use the (-)ss RNA to produce more progeny +ss RNA = Stage 2 |
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What are the steps involved in (-)ss RNA viral genome replication?
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Parental (-)ss RNA enters cytoplasm
Viral RNA polymerase produces +ss RNA (aka viral mRNA) = Stage 1 SIMULTANEOUSLY: Ribosomes translate & synthesize proteins from the +ssRNA WHILE RNA polymerase produces more progeny (-)ssRNA |
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What effect does the longevity of DNA have on the types of infections it causes?
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Many DNA viruses establish persistent infections
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Where do DNA viruses replicate? What is the 1 exception?
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Replicate in host cell nucleus
Exception is pox virus |
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What is the general trend in the types & timing of proteins encoded for by DNA viruses?
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Early genes encode for non-structural binding proteins, such as DNA-binding proteins, enzymes, etc.
Later genes encode for structural proteins |
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What is the relationship between viral size & replication in DNA viruses?
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The smaller the DNA virus, the more dependent the virus is on host cellular mechanisms for transcription/translation/replication
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dsDNA virus replication is characterized by what factors? Give some examples of these types of viruses.
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Directly utilize cellular enzymes to transcribe viral RNA & translate viral proteins within the nucleus
Naked viral DNA genomes are infectious by themselves in susceptible/permissible cells Early transcription/translation produces regulatory viral proteins Late transcription/translation produces structural proteins. Papovaviridae, Adenoviridae, Herpesviridae |
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What are the unique characteristics associated with pox virus replication?
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Poxviruses are the largest viruses & carry all the components necessary for replication/transcription/translation within the virion
Host transcriptional factors are NOT needed so FULL replication can take place in the Cytoplasm Initial transcription & translation occur within the virion core! |
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ssDNA virus replication is characterized by what factors? Give some examples of these types of viruses.
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Replication depends on the HOST cells much more than larger viruses
Autonomous parvoviruses replicate efficiently ONLY in the nucleus of rapidly-dividing cells (hence the disease it causes) Adeno-associated parvoviruses replicate only in cells CO-infected with adenoviruses Replication involves the synthesis of complementary DNA to the parental DNA in the Nucleus with subsequent transcription of the viral DNA genome. |
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What inherent factors in viral genetics/replication contribute to their mutation ability?
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Poor fidelity of viral polymerase
Rapid rate of genome replication RNA viruses especially lack proof-reading mechanisms |
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Match the term with its definition:
Wild-type Newly isolated virus types from the host Field isolates Different wild-types of the same virus Strains Original virus Variant virus strains new virus strains derived from spontaneous mutation that are different from the parental wild-type |
Wild-type = Original Virus
Field Isolates = Newly isolated virus from the host Strains = Different wild-types of the same virus Variant Virus Strains = New Virus strains derived from spontaneous mutation that re different from the parental wild-type |
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What are all the different "-types" that a virus can be classified by?
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Serotype
Genotype Biotype Pathotype |
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What are the 2 main types of mutations that may occur in viruses (and in any biological system, really)?
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Spontaneous mutation
Induced mutation |
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What is the spontaneous mutation rate of DNA viruses versus RNA viruses?
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DNA = 10-8 to 10-11
RNA = 10-3 to 10-4 |
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What are 7 important types of mutations that viruses may undergo?
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Host range mutation
Drug Resistance mutation Antibody escape mutation Revertants Lethal mutations Deletion Mutations Temperature-sensitive mutations |
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What type of mutation would result in a cross-species infection?
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Host range mutation
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What type of mutation would result in failure of chemotherapeutic treatment of a virus?
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Drug resistance mutation
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What type of mutation would help a virus avoid the host's immune system?
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Antibody escape mutation
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What type of mutation could result in the iatrogenic infection of an animal with a deadly viral infection?
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Revertant mutation
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What type of viral mutation would most benefit the host?
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Lethal mutation
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What mutation would be helpful in vaccine development for reduction in virulence?
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Deletion mutation
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What mutation would be helpful for isolating a virus within a particular biological zone?
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Temperature-sensitive mutation
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What occurs during phenotypic mixing?
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The viral genome from 1 virus is enclosed in the capsid/envelope of another virus during a mixed viral infection
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What is the process known as when the total yield of virions produced in an infection remains constant by the number of Infectious virions diminishes?
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Interference.
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Activation of cellular Oncogenes & the development of tumors & cancers occurs due to what genetic interaction process?
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Integration, where the viral genome integrates into the cellular genome
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What is "Persistence" in relation to viral genetic interactions?
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A change in either the virus or the cell in which the virus is able to replicate within the cell without the cell being killed/lysed.
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What is the process of intramolecular genetic exchanges between viruses resulting in new viruses or variants?
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Recombination
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What is reassortment?
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The exchange of genetic material between viruses resulting in a new hybrid virus
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What is the primary different in viral genomes between recombination & reassortment?
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Recombination occurs in NON-segmented viral genomes where Reassortment occurs in Segmented viral genomes
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What is CPE & why is it important?
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CPE = Cytopathic Effect
Refers to the morphological changes viral infected cells undergo Changes include rounding, lysis, detachment, syncytia, inclusion bodies |
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What causes CPE?
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Direct pathological injury of the infected cell
Side effects of altered metabolism due to virus replication |
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What structures are considered VAPs in enveloped vs non-enveloped viruses?
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Enveloped = spike or peplomer glycoproteins present on the envelope
Non-enveloped = proteins extending from the capsid/part of the capsid |
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What significance do cell receptors have on viral infectivity?
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Receptors on host cells determine host range, tissue tropism, etc.
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What is the chemical composition of host cell receptors?
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Proteins
Carbohydrates on glycoproteins Glycolipids |
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What are the general processes/effects of Penetration & uncoating?
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1. Fusion/Endocytosis/Translocation
2. Nucleocapsid is disintegrated 3. Viral genome is freed in cytoplasm 4. Capsid proteins disintegrate in cytoplasm 5. After uncoating, synthesis of viral proteins via cellular metabolism occurs |
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What RNA viruses are the exception to the rule of all RNA viruses undergoing replication in the cytoplasm?
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Orthomyxovirus
Coronavirus Retrovirus |
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What effects do viruses have on host cell metabolism?
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Inhibition of cellular transcription mechanisms (i.e. cells do not transcript their own material?)
Inhibition of RNA processing pathways Inhibition of Cellular translation Inhibition of Host Cell DNA synthesis |
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What effects do viruses have on host cell structures?
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Membrane fusion between neighboring cells
Chaning the permeability of the cell plasma membrane Disruption of cytoskeletal fiber system, microfilaments and microtubules (rounding of cell) Cytoskeletal components incorporated into infected cell structures as inclusion bodies |
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Define "enzootic"
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Multiple, continuous transmissions of disease and disease presence in a defined population/region/time
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Define "epizootic"
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peaks in incidence of disease exceeding the endemic baseline. The nature & degree of damage defines whethter it is considered Epizootic or Enzootic
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Define "panzootic"
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Worldwide spread of disease
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Rate of disease in a population is defined as what?
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Number of cases/total number in population.
Different diseases have different rates |
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The number of cases over the number of subjects exposed for a period of time is known as the what?
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Incidence or Attack Rate
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Incidence/Attack Rate is typically a measurement used for what types of diseases? Why?
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Acute, short duration diseases?
Because there is a time component in the denominator, thus it is inherently more difficult to measure incidence/attack rate over long periods of time (i.e. chronic disease) |
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TRUE/FALSE: Prevalence only measures the number of cases in a define number of subjects and is therefore more useful when measuring chronic, long duration diseases.
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TRUE!!!
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What is the incubation Period?
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Time frame form the Moment of Infection to the Onset of Clinical Signs
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What is Generation Time?
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Time frame measured from the moment of infection to the first moment of shedding the virus.
Most Generation times are shorter than incubation periods |
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What is the period of infectivity?
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Time frame measured from the First day of viral shedding to the last day of shedding.
May or may not be longer than clinical disease |
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What are the primary modes of transmission of viral disease?
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Horizontal
Vertical Zoonotic Vector-borne Iatrogenic Nosocomial |
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What are some methods of Horizontal transmission?
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Direct contact
Indirect contact Common vehicle Airborne |
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Which method of horizontal transmission are enveloped viruses most likely to use? Non-enveloped?
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Enveloped = Direct contact
Non-enveloped = Indirect contact |
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What are the most common sources of vertical transmission of viruses?
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Placenta
Perinatal transmission (i.e. the birth canal) Colostrum Milk |
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What mode of transmission can have viruses pass from generation to generation, genetically speaking?
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Germline transmission
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What are the benefits of using a Biological vector over a mechanical vector for viral transmission?
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Biological vector = viruses are able to replicate & magnify within the vector for increased efficiency of transmission.
Mechanical vector = There is no replication of viruses |
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What are some examples of families of Arboviruses?
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Togaviridae
Flaviviridae Bunyaviridae Reoviridae Rhabdoviridae |
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How do you define Zoonotic transmission?
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Viral diseases that are transmitted under Natural conditions from vertebrate animals to humans
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What are the 2 most preventable modes of virus transmission?
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Iatrogenic & Nosocomial
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How does the skin function as a natural barrier to transmission?
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The epidermis, composed of dead, keratinized cells, provides a medium in which viruses cannot grow & spread
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What are some examples of viruses whose primary site of action/disease is the skin?
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Herpesvirus
Papillomavirus Poxvirus |
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What barriers are present in the Respiratory tract to prevent disease transmission?
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Mucus
Mucocilliary movement Neutrophils & Macrophages IgA & other cell-mediated immunity mechanisms Physical characteristics - Limited size of particles that can penetrate lungs; air currents, humidity, temperature (colder than core body temp) |
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What are some examples of viruses whose primary site of infection is the respiratory tract?
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Adenovirus
Coronavirus Herpesvirus Calicivirus Orthomyxovirus Paramyxovirus Picornavirus |
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What barriers exist in the GI tract to prevent disease transmission?
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Low pH
Proteases Bile salts Mucus IgA & Cell-mediated immunity factors Enzymatic enhancement |
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What are some examples of viruses whose primary site of infection is the GI tract?
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Adenovirus
Calicivirus *Coronavirus* Picornavirus Reoviridae Toroviridae ***Non-enveloped viruses -> more resistant*** |
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What barriers are present in the Urogenital tract to prevent disease transmission?
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Mucus
IgA Cell-Mediated Immunity |
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What are some examples of viruses whose primary site of infection is the Urogenital tract?
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Papillomavirus
Herpesvirus Togavirus |
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What barriers are present in the conjunctive that act to prevent disease transmission?
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TEARS!
IgA IgG |
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Though conjunctival transmission is not a major route of infection, what viruses may employ this route of transmission?
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Herpesviridae
Adenoviridae |
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What are the 3 major routes through which viruses may spread throughout multiple body systems?
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HEMATOGENOUS SPREAD!
Lymphatic spread Neural spread |
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Viruses are typically shed through body orifices. What effects might a local vs a systemic infection have on where viruses are shed from?
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Local infections = local shedding
Systemic infections = multiple points of shedding |
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What 2 factors primarily define the outcome of infection in relation to viral shedding?
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Amount of shedding
Timing of shedding |
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What are all of the most common routes of virus shedding?
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Skin/Dermal
Respiratory secretions Saliva Feces Genital secretions Urine Milk |
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Of the routes for virus shedding, which is the most important?
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Respiratory
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What are some examples of viruses shed through saliva?
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Rabies
FIV |
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What are some examples of viruses shed in the urine?
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Rinderpest
FMD Canine hepatits Hantavirus |
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What are some examples of viruses that are NOT shed typically?
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Encephalitis viruses
Retroviruses |
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What are some host factors that contribute to the differences outcomes of viral infections?
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Age
Sex Reproductive status Immune status Nutritional status Genetics |
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Viral proteins & glycoproteins that induce a host immune response are known as what?
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Antigens!
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What are epitopes?
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AKA: Antigenic Determinants.
Discrete parts or components of viral proteins that elicit neutralizing antibodies |
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What are the 2 major types of T lymphocytes?
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Helper/Regulator T cells
Cytotoxic/Effector T cells |
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MHC-I and II proteins are found where?
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MHC-I = plasma membrane of MOST cells
MHC-II = present on Antigen Presenting Cells |
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What are cytokines & what is their function?
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Soluble proteins produced by T cells, macrophages & monocytes
Regulate, augment or suppress immune responses Inhibit or enhance viral gene expression |
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An anamnestic immune response occurs when and from what primary cell type?
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Occurs when an animal is exposed to an antigen for a second time.
Primary cell type involved = memory T cell |
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What are some primary characteristics of Natural Killer cells?
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Large granular lymphocytes that destroy virus-infected cells
No specificity in cells that they destroy No memory of antigens No dependence on MHC or antibody recognition |
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What are complement(s) and what is their function?
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Serum components (proteins) that complement the immune response
Enhance destruction of virus-infected cells, inflammation, opsonization and neutralization |
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What are the 2 different types of immunity that animals possess?
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Active immunity
Passive immunity |
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What processes are involved in active immunity?
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Destruction of infected cells
Neutralization of infectious viruses Production of INF |
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What processes are involved in passive immunity?
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Passive transfer of antibodies/activated T cells into the host
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What are the 4 mechanisms of Immune cytolysis of Virus-Infected Cells?
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Cytotoxic T cells release perforin to disrupt cell membrane integrity
Antibody-complement complex mediated cytotoxicity Antibody-dependent cell-mediated cytotoxicity (on leukemoid cells) Natural killer cells activate and non-specifically kill viral-infected cells |
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What are the 2 most common methods of viral neutralization?
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Neutralization at the attachment/entry stage by antibody-mediated blocking of receptor interaction
Neutralization by destruction via cellular enzymes triggered by antibody-virus complexes |
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What antibody is primarily involved in local, mucosal diseases?
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IgA
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What antibody is primarily involved in systemic infections?
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IgG
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Why should you be careful when vaccinating young animals (besides the obvious)?
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Passive immunity from maternal antibodies may prevent young animal from mounting proper immune response to vaccine
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What are the important characteristics of IgA?
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Secreted in respiratory and GI secretions
Important in localized infections Maternal/lactogenic immunity -> Are present in colostrum initially, but rapidly decline |
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What are the important characteristics of IgG?
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Capable of transplacental/translocation across GI
Provide systemic protection from disease & viremia Lose their activity upon digestion in GI tract Short duration/lifespan associated with Translocation Maternal IgG is rapidly destroyed in newborns |
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What are the primary considerations in human vaccination?
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Safety, efficacy are highly controlled and of top priority
Cost per dose is low priority Small number of vaccines available Worldwide campaign |
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What are the primary considerations in animal vaccinations?
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Cost is a top priority
Safety & efficacy are important, but not as highly regulated as human (?) Limited international efforts |
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What are the 4 main types of vaccines used in Veterinary Medicine?
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Modified live-attenuated
Killed Subunit Genetically engineered/recombinant |
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What is the most effective type of vaccine used in veterinary medicine?
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Modified live
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What routes of administration can be used with MLV?
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SC
IM orally Aerosol Water |
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What are the risks associated with use of MLV?
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Insufficient attenuation of pathogenic virus may cause disease we're trying to prevent
Contamination with adventitious live virus Reversion to virulence |
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What are the disadvantages of using a Killed vaccine?
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Incomplete activation of host immune system
Requires multiple injections Produces a lower level & shorter duration of immunity |
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What are adjuvants?
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Immune enhancers mixed with subunit, inactivated, synthetic vaccines to enhance immunogenicity
Act via prolonged retention & slow release, macrophage activation, & attraction of lymphocytes & lymphokine secretion |
