6 – How do Viruses Infect and Spread Through the Body? Flashcards

1
Q

Many viruses enter through respiratory tract

A
  • Where they are deposited depends on SIZE
  • At each level, viruses may infect EPITHELIAL CELLS
    o Can lead to disruption of mucociliary escalatory and ‘secondary’ bacterial infections
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2
Q

Droplet vs airborne transmission

A
  • Droplet: Coughs and sneezes can spread droplets of saliva and mucus
  • Airborne: tiny particles are suspended in air for longer and travel further
    o **VERY IMPORTANT FOR VIRUSES (ex. dog kennels)
    o Ventilation is very important
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3
Q

Many viruses are ingested

A
  • Many that cause intestinal infection are acid and bile RESISTANT
  • Acid may increase infectivity by cleaving capsid
  • Peristalsis moves viruses along: provides contact with target cells
  • *virus can enter M cells (immune system): parvovirus reach epithelium through blood
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4
Q

Viruses enter via the skin

A
  • Skin is the longest organ
  • Intact keratinized skin=tough barrier, but
    o Cuts, injuries provide entry
    o Iatrogenic: dirty needles
    o ‘flying needles’ (mosquitoes) and other arthropods transmit ‘arboviruses
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5
Q

Mechanism of spread in body

A
  • Local spread on epithelial surface
  • Spread in respiratory tract enhanced by fluid layer
  • Spread in GI tract enhanced by fluid layer and peristalsis
  • Subepithelial invasion and lymphatic spread
  • Spread via blood stream=viremia
  • Interact with macrophages
  • Interact with endothelial cells
  • Multiple within the CNS
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6
Q

Local spread on epithelial surfaces

A
  • Many pox viruses (ex. myxoma virus, papilloma virus)
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7
Q

Spread in respiratory tract enhanced by fluid layer: example

A
  • Ex. BRSV
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8
Q

Spread in GIT enhanced by fluid layer and peristalsis: example

A
  • Ex. coronavirus
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9
Q

Subepithelial invasion and lymphatic spread

A
  • Facilitated by basolateral budding from epithelial cells
  • Ex. mouse hepatitis virus (coronavirus)
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10
Q

Spread via blood stream=Viremia

A
  • May be free in plasma or associated with cells
  • Play a central role in many viral infections, but NOT ALL
  • Often viruses with primary and secondary are more ‘susceptible’ to vaccination b/c of LONGER incubation period=gives time for memory response
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11
Q

Primary and secondary viremia

A
  • Primary: first entry may be subclinical
  • Secondary: following replication in target tissue higher sustained levels
  • *don’t cause disease right away
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12
Q

Viruses interaction with macrophages

A
  • Differences amongst isolates of same virus in their ability to infect macrophages
  • Ex. feline coronaviruses
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13
Q

Virus interactions with vascular endothelial cells

A
  • Route to parychymal organs from blood
  • Ex. bluetongue virus
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14
Q

There are multiple mechanisms of spread within the CNS

A
  • Peripheral nerves=one important route of infection for viruses in affect CNS (ex. rabies)
    o Don’t need to pass BBB
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15
Q

Mechanisms of virus shedding

A
  • Shed from respiratory tract
  • Shed from oropharynx and GI tract
  • From skin
  • Urinary tract
  • Genital tract
  • milk
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16
Q

Shedding from respiratory tract

A
  • Coughing, sneezing, eating, drinking
  • Ex. parainfluenza, BHV-1, BRSV
17
Q

Shedding from oropharynx and GI tract

A
  • Few in saliva: ex. rabies virus
  • Feces: ex. rota, corona
18
Q

Shedding from skin

A
  • Abrasions (ex. poxviruses, papilloma)
  • Form lesions (ex. FMDV)
  • Feather follicle (ex. Marek’s disease)
19
Q

Shedding from urinary tract

A
  • Results from replication in kidney
  • Ex. Hanta virus
  • Ex. canine hepatitis (adenovirus)
20
Q

Shedding from genital tract

A
  • STD
  • Viruses shed in seme (ex. equine viral arteritis)
21
Q

Shedding in milk

A
  • Usually cell-associated
  • Ex. small ruminant lentiviruses
  • Ex. CAE
  • Ex. M-V
22
Q

What is tropism?

A
  • Capacity of virus to selectively PERMISSIVELY infect cells in a particular organ
  • *depends on presence of receptors and intracellular environment