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16 Cards in this Set
- Front
- Back
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What are the six levels of infection?
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Iceberg concept of infection
Death of an animal Severe disease Moderate disease Mild disease Subclinical disease Exposure without infection |
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Define virulence and pathogenicity?
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Virulence is used as a quantitative or relative measure of the pathogenicity of the infecting virus (pathogenic or nonpathogenic).
The terms pathogenicity is used to describe the capacity of a virus to cause disease in the host animal. |
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How do you assess viral virulence?
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The dose of the virus required to cause death in 50% of infected animals is called lethal dose 50 (LD50).
It is a valuable measure of the character of the virus. ID50: the dose of a particular strain of virus that causes infection in 50% of individuals. Viral virulence can also be measured in experimental animals by determining the ratio of the dose of ID50 to dose of LD50 (ID50/LD50) TCID50: It is the infectious dose that cause cytopathic effect (CPE) in 50% of the infected tissue cultures. |
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What is acute infection?
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It is a race between the capacity of the virus to replicate, spread in the body, and cause disease versus the capacity of the host to curtail and control these events.
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What are the viral genes that can maximize the yield of virions?
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Transcription regulators
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What are the viral genes essential for virus replication?
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virus entry
replication of viral genome production of viral protein assembly/release of new virions |
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What do virokines do? How do they do it? What cytokines do they inhibit and which do they mimic?
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It influences the pathogenesis of the infection in vivo by sabotaging the body’s innate resistance or immune response by function as:
-Inhibitors of T cell cytotoxicity by binding to nascent class I MHC in ER. -Inhibitors of cytokines: IL-1, IFN-g, TNF. -Inhibitors of antibody-mediated cytolysis. -Inhibitors of the complement cascade. -Cytokine mimics: IL10 to suppress host response. |
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What is resistance or susceptibility of individual animals within a susceptible population determined by?
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-Genetic constitution
-Immune response -Cell differentiation -Cellular receptor -Age -Hormonal factors -Fever -Multiple infection (shipping fever - where normal flora can turn bad) |
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How do genetic difference influence the resistance of individuals within susceptible populations?
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Host response to different virus is influenced by either a dozen genes or a few genes.
Common viral infections often tend to be less pathogenic in their natural host species than in exotic or introduced species. |
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How does immune responsiveness influence the resistance of individuals within susceptible populations?
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Immune responsiveness to particular viral infections differs greatly from one individual animal to another, being under control of specific immune response (Ir) genes.
MHC region Gene encodes interferons Macrophages Cellular receptors TNF-a (M, NK), TNF- b (T) and Interferons |
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How do cellular receptors influence the resistance of individuals within susceptible populations?
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Cellular receptor expression on target cells is a fundamental determinant of host resistance/susceptibility to the particular virus.
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How does cell differentiation influence the resistance of individuals within susceptible populations?
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1). Vesicular stomatitis and distemper viruses, which do not replicate in normal resting PBL, but do so when cells differentiated after activation by mitogen.
2). Maedi/visna infects monocytes abortively with low levels of transcription of viral RNA, but the infection becomes productive as the cells differentiate into macrophages 3). Papillomaviruses: productive infection is not seen in the deeper layers of the epidermal tumor, but occurs only when the cells become keratinized as they move to the surface layers of the skin. 4). Parvoviruses replicate only in cells that are in the late S phase of the cell cycle (therefore the rapidly dividing Bone marrow cells are most vulnerable, eg. FPV) |
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How does age influence the resistance of individuals within susceptible populations?
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New-borns and young ones are particularly vulnerable to infections with certain viruses!
Canine distemper virus Canine parvovirus Swine transmissible gastroenteristis virus Hog cholera virus Bovine viral diarrhea virus Enteropathogenic coronaviruses (many animals) Rotaviruses (many animals) Herpesvirus (many animals) |
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How do hormones and pregnancy (or stress) influence the resistance of individuals within susceptible populations?
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Stresses cause adrenocortical immunosuppression.
Immunosuppression with corticosteroids reduce inflammatory and immune response, dampen macrophage action, and depress interferon synthesis. Rift valley fever virus infection in pregnant dam Herpesvirus infection may be reactivated during pregnancy |
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How does fever influence the resistance of individuals within susceptible populations?
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Almost all viral infections are accompanies by fever.
Changes environment to make it less hospitable for pathogen. |
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How do multiple infections influence the resistance of individuals within susceptible populations?
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Viral infections of the respiratory tract often predispose animals to bacterial infection:
Sipping fever: often initiated by a variety of respiratory viruses and other stressors, but its serious consequences are due to secondary infection with pasteurella multocida or hemolytia. |
