7 – How do Viruses Cause Disease? Flashcards

1
Q

How do viruses evade host defences?

A
  • Noncytocidal infections
  • Cell to cell spread (membrane fusion)
  • Infection of non-permissive, resting or undifferentiated cells
  • Infection with restricted gene expression=latency
  • Destruction of immune effector cells and macrophages
  • Down-regulation of MHC molecule expression
  • Induction of non-neutralizing antibody
  • Induction of immunologic tolerance
  • Sequestration in immunological privileged tissues (brain)
  • Integration of viral genome into host cell genome
  • Genetic/antigenic drift
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2
Q

Noncytocidal infections

A
  • Chronic infections w/o killing cells in where replication occurs
  • Ex. hantavirus (in the mouse)
    o Mice don’t get sick, can be fatal in humans
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3
Q

Cell to cell spread (membrane fusion)

A
  • Hides from hosts immune mediators
  • Ex. morbilliviruses (CDV< measles)
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4
Q

Infection of non-permissive, resting or undifferentiated cells

A
  • Virus undergoes productive infection in one cell type but NONproductive infection in another
  • Ex. papillomavirus (basal cells vs. keratinocytes)
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5
Q

Infection with restricted gene expression=latency

A
  • Ex. herpesviruses
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6
Q

Destruction of immune effector cells and macrophages

A
  • Ex. lentiviruses (immunodeficiency viurses)
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7
Q

Down-regulation of MHC molecular expression

A
  • Leads to reduced ability to be killed by CD8+ T-cells
  • Ex. adenovirus
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8
Q

Induction of non- neutralizing antibody

A
  • May enhance uptake
  • Ex. Aleutian disease
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9
Q

Induction of immunologic tolerance

A
  • Ex. BVDV
    o If 1st trimester=recognize as self
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10
Q

Sequestration in immunologically privileged tissues (brain)

A
  • Ex. rabies
  • Ex. herpesviruses
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11
Q

Integration of viral genome into host cell genome

A
  • Ex. retroviruses
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12
Q

Genetic/antigenic drift

A
  • Ex. lentiviruses
  • Ex. influenza
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13
Q

Many viruses that are non-cytopathic in vitro produce LETHAL disease in vivo

A
  • Often associated with “out-of-control” innate immune response
    o Cytokine storm
    o Response= the disease
  • Ex. BVDV
  • *depending on organ, cell and tissue, damage can occur w/o clinical signs (ex. in the liver)
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14
Q

Direct tissue and organ damage systemically (viruses at tissue/organ level)

A
  • Not a good thing in vital organs
  • Ex. Ebola virus
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15
Q

Damage to epithelium in the respiratory tract (viruses at tissue/organ level)

A
  • Compromise gas exchange
  • Damage mucociliary escalator->secondary infections
    o Ex. BRSV
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16
Q

Damage to epithelium in GI tract (viruses at tissue/organ level)

A
  • Disrupted fluid absorption
  • Fluid loss=dehydration
  • Ex. coronavirus
  • Ex. rotavirus
17
Q

Damage to CNS (viruses at tissue/organ level)

A
  • Direct neuronal damage
    o Ex. West Nile virus
  • Ischemic injury: due to endothelial cell infection
    o Ex. EHV-1
18
Q

How does virus infection damage the immune system? (primary lymphoid organs: thymus and bursa)

A
  • Deplete T and B cells
  • Ex. BVDV
19
Q

How does virus infection damage the immune system? (secondary lymphoid organs)

A
  • Immunosuppression
  • Very common and IMPORTANT
  • Ex. FeLV, FIV, BVDV, CDV
20
Q

How does virus infection damage the immune system? (hypersensitivity Type III)

A
  • Type III (immune complex) most important
  • Ex. Aleutian disease (parvovirus)
  • Ex. FeLv
  • Ex. FIP
21
Q

Inflammation is a ‘double-edged’ sword

A
  • Blessing and a curse!
  • *disease is often the result of HOST RESPONSE (inflammation)
22
Q

(certain) RNA viruses can cause cancer by somehow manipulating

A
  • Cellular oncogenes
23
Q

(certain) DNA viruses can cause cancer by encoding for

A
  • Oncogenic proteins
24
Q

Oncogenes

A
  • Genes that are cellular or viral in origin
  • Associated with oncogenic transformation of cells
  • *cellular ones=normal
    o If altered in expression or amplification will cause inappropriate expression leading to cell TRANSFORMATION
25
Q

Viral oncogenes

A
  • Derived from cellular oncogenes, but often CONTAIN MUTATIONS that effect the host cells ability to control the viral oncogene expression
26
Q

What do oncogenes influence or act as to effect cell growth control?

A
  • Growth factors
  • Receptors
  • Intracellular transducers
  • Intranuclear factors
27
Q

Tumor suppressor genes

A
  • Produce proteins that are involved in negative control of cell growth
  • Ex. p53 associated with a wide-variety of cancers
  • *viruses only implicated in a minority of tumors with alterations to tumor suppressor genes
    o Certain viruses produce viral products that alter effect or regulation of these genes