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VIROLOGY > 8 – What factors contribute to viral virulence and host resistance? > Flashcards

8 – What factors contribute to viral virulence and host resistance? Flashcards

1
Q

Virulence

A
  • Quantitative measure of PATHOGENICITY
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2
Q

Pathogenicity and virulence refer to a disease-causing potential NOT

A
  • Infectiousness or transmissibility
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3
Q

Just b/c a virus is easily transmissible does NOT mean it will be

A
  • Virulent or even pathogenic
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4
Q

Determinants of viral virulence are usually

A
  • Multigenic
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5
Q

Determinants of host resistance/susceptibility are usually

A
  • Multifactorial (multigenic)
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6
Q

Virus strain differences may be quantitative or qualitative involving

A
  • Organ or tissue TROPISM
  • Efficacy of spread
  • Character of disease
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7
Q

Within a population, what does resistance/susceptibility of individuals vary with?

A
  • Genetic makeup
  • Age
  • Nutritional status
  • Level of stress
  • Hormonal factors
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8
Q

What are precise measures of virulence usually derived from?

A
  • Assays in inbred animals (mostly mice)
  • *limited by what viruses grow in mice
    o Need to be careful with too much extrapolation
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9
Q

LD50

A
  • Does required to cause death in 50% of animals
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10
Q

ID50

A
  • Dose required to infect 50% of animals
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11
Q

What are the determinants of viral virulence? (3)

A
  1. Tropism
  2. Viral enhancers, promoters, and transcription factors (non-structural proteins)
  3. Virokines
    *largely still a black box
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12
Q

Tropism

A
  • Broader tropism=generally more virulent
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13
Q

Viral enhancers, promoters and transcription factors (non-structural proteins)

A
  • Increases efficiency of viral replication
  • Higher viral load»>more virulent, but NOT always
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14
Q

Virokines

A
  • Found in large DNA viruses
  • Most mimic activity of soluble mediators of the immune reponse
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15
Q

How virulent does a virus ‘want’ to be?

A
  • Evolutionary trade-off between virulence and transmissibility
  • Difficult to know what will happen when it jumps to a new species
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16
Q

What can happen to virulence when a virus ‘jumps’ hosts? (3)

A
  • More virulent (ex. simian immunodeficiency virus to humans)
  • Less virulent (infectious hematopoietic necrosis virus to rainbow trout)
  • No change in virulence (equine influenza to dogs)
17
Q

What are determinants of host resistance/susceptibility?

A
  • Genetic differences (most obvious between species, ex. blue tongue virus)
  • Immune response genes
  • Inherited immunological nonresponsiveness
  • Cellular receptors
18
Q

Immune response genes (host resistance/susceptibility)

A
  • Polymorphism in MHC
  • Polymorphism in genes coding for interferon, interferon responsiveness and interferon inducible genes
19
Q

Inherited immunological nonresponsiveness (host resistance/susceptibility)

A
  • SCID foals: adenovirus
  • Selective IgA deficiency
  • Rottweilers and Dobermans: parvovirus?
20
Q

Cellular receptors (host resistance/susceptibility)

A
  • Species and individual differences
  • *Viruses evolve to use different receptors
  • Ex. species differences in AA composition of ACE-2 receptor determine host range of SARS-CoV-2
21
Q

What are the 3 layers of protection that prevent infectious agents from invading and colonizing?

A
  • Physical/physiological barriers
  • Innate immune responses
  • Acquired immune response
22
Q

What are the components of the ‘barrier’ in the bovine respiratory tract?

A
  • Mucins
  • Antimicrobial peptides
  • Oxidative defense system
  • *gut: non-specific functions too (ie. Microbiome)
23
Q

Innate immunity

A
  • Early recognition to non-self
  • Brings effector cells to site of invasion of microorganisms
  • Targets the invaders for destruction by effector mechanisms
  • *PAMPs
  • *PRRs
  • *many viruses encode non-structural proteins that INHIBIT INTERFERON PATHWAYS
24
Q

PAMPs

A
  • Pathogen associated molecular patterns
  • Recognized biochemical structures not found in vertebrae cells
  • Trigger innate immune reponses or inflammation
25
Q

Generally the (life) style of the pathogen determines the immunological response

A
    1. Cell mediated: Intracellular pathogens (viruses)
    1. Humoral (B-cell): extracellular pathogens (bacteria)
  • *why use killed vaccines for bacteria and live vaccines for viruses
26
Q

What do B-cells recognize?

A
  • Epitopes via IgM
27
Q

How do T-cells recognize the virus?

A
  • CD4: MHC II
  • CD9: MHC I
28
Q

IgG

A
  • Really good a virus NEUTRALIZATION
  • Pro-inflammatory
29
Q

IgA

A
  • Mucosal surfaces
  • Neutralizes microbes and toxins
30
Q

Passive immunity

A
  • Colostrum contains Abs and non-specific inhibitors
  • *need to vaccinate puppies 3 times as we don’t know when the puppy does NOT have maternal Abs blocking it
31
Q

Acquired immune response

A
  • Cell-mediated immunity
    o Involves BOTH CD8 and CD4 T cells
  • *enhanced by previous exposure or vaccination
32
Q

Somatic mutation (B lymphocytes)

A
  • B lymphocyte responses evolve over time in the SAME individual
  • *each time an animals ‘sees’ an antigen=develops a ‘better’ Ab response
    o Those that bind it good=go on
  • *BOOSTERS
33
Q

T-cells and improvement

A
  • NONE
  • Thought behind it: decreased chances for autoimmunity
34
Q

What physiological factors affect host resistance/susceptibility?

A
  • Age
  • Nutritional status
  • Hormones and pregnancy
  • Fever
  • Multiple infections
35
Q

Corticosteroid therapy (host resistance/susceptibility)

A
  • Decreases immune responses
  • *more concerned with chronic exposure
36
Q

Fever (host resistance/susceptibility)

A
  • IL-1 mediated
  • *protective response
  • If block fever=can increase severity of infection
37
Q

Multiple infections examples(host resistance/susceptibility)

A
  • Shipping fever
  • Kennel cough
  • PMWS

VIROLOGY (12 decks)

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