Viral Pathogenesis Flashcards

1
Q

What are the stages of viral pathogenesis and infection?

A
  • Animal vs Cell
  • Entry into the host - Absorption
  • Primary replication - Penetration
  • Spread through the host - Uncoating
  • Cell and tissue tropism - transcription
  • Host immune responses - Translation
  • Secondary replication - Replication
  • Cell injury - Assembly
  • Persistence - Release
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2
Q

What is the Cytopathic effect?

A
  • Can be seen in cell culture as:
    • Cytoskeletal disruption
    • Inclusions
    • Syncytia
    • Necrosis
    • Apoptosis
    • Lysis
  • CPE caused by virus infection is not an unintended consequence of virus infection on the host cell
  • Normally part of the virus infection/replication process
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3
Q

What is an Inclusion body?

A
  • Viral replication complexes in the nucleus or in the cytoplasm
    • Cells may stay intact, but form “inclusion bodies”
    • Inclusions are assembled in the nucleus or cytoplasm for synthesis of viral nucleic acids and assembly of virions
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4
Q

What is a Syncytium?

A
  • Fusion of cells into a single multinucleated cell
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5
Q

Why study infection of cells?

A
  • Diagnostic tool
  • Obtain a pure virus culture
  • Understand basic biological process related to pathogenesis
  • Develop and test antivirals and vaccines
  • Replace the use of live animals
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6
Q

How do viruses cause disease?

A
  • Virus enters the host
  • Primary replication of the virus
  • Spread in the host
  • Fate of the virus infection
    • cleared
    • persistent
    • Acute
    • Benign
  • Transmission to another host
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7
Q

What do viruses need for a successful infection?

A
  • Enough virus to infect
  • Susceptible and permissive cells
  • Host defenses must be compromised or not effective
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8
Q

How many virions are enough to cause infection?

A
  • Varies a lot with the host and the virus
    • Health of host - immune compromised
    • Age of Host - young or old
    • Behavior of host - outside a lot for vector-borne viruses
    • Virulence of the virus
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9
Q

How do viruses survive outside a host?

A
  • Some don’t
  • Some stay in body fluids or fecal-oral
  • Some survive the environment
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10
Q

How can a Virus enter the host?

A
  • Something needs to compromise the barrier for the virus to infect
  • Virus get through the skin or mucosal membranes:
    • Skin - puncture
    • Eye - conjunctiva infected
      • blinking is a host defense
    • Alimentary tract - abrasions
    • Urogenital tract - abrasions
    • Mucosal Membranes of the Respiratory tract
      • does have host defenses such as mucus, cilia, macrophage
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11
Q

Why is the skin a good barrier to viruses?

A
  • low pH 5.5
  • other microorganisms
  • also desiccates the virus
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12
Q

Which viruses enter through the skin?

A
  • Poxviruses - mouse, cow, rabbit infect through breaks in the skin
  • Papillomavirus - sexual contact
  • Rhabdovirus - Animal bite
  • Arboviruses - via the bite of an infected arthropod
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13
Q

How do viruses enter through the respiratory tract?

A
  • Barriers:
    • Mucus, cilia
    • Humoral and cellular immunity
  • Viruses enter through droplets of saliva
  • Environmental factors are important to stability of aerosolized virions
    • Temperature
    • humidity
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14
Q

What viruses enter through the respiratory tract?

A
  • Upper:
    • Arenaviruses, coronaviruses, respiratory syncytial virus (RSV), coxsackievirus
  • :Lower
    • RSV, Influenza
  • Entry to respiratory tract leading to systemic spread:
    • Hantavirus, poxvirus, arenaviruses
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15
Q

How is the GIT susceptible to infection?

A
  • Small intestine is a selectively permeable barrier
  • There is direct contact with the outside
  • Contains polarized epithelial cells
  • Localized Infections:
    • stay in the epithelial cells next to the intestinal lumen
      • Coronavirus, rotaviruses
  • Systemic infections:
    • spread within the host
      • enterovirus, reovirus, adenovirus
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16
Q

How is the Urogenital Tract susceptible to viral infections

A
  • Compromised epithelium can allow virus entry
  • Localized:
    • papillomavirus
  • Systemic:
    • Hepatitis B
    • herpes simplex virus
    • HIV
17
Q

How is the Conjuctiva susceptible to viral infections?

A
  • Normally a localized infection of the eye
    • adenovirus
  • Systemic infections can occur in the virus disseminates
    • Herpes simplex virus
    • enterovirus
18
Q

What are the types of infections?

A
  • Acute
  • Latent
  • Progressive
  • Chronic or persistent
  • Failure to clear all evidence of infection
19
Q

What are the steps in a viral infection?

A
  • Entry into host and primary virus replication
  • Local or general spread in the host with secondary virus replication
  • Shedding from host
  • Clearance from the host
20
Q

What is the difference between localized and systemic infections?

A
  • Localized:
    • virus stays close to the site of entry to replicate and spreads within the epithelium
    • virus is restricted to where it first infected
  • Systemic:
    • Virus disseminates to infect other organs
21
Q

How do viruses spread within a host?

A
  • Viruses pass through the basement membrane can get to blood vessels and lymphatic vessels
  • Spreads to other tissues
22
Q

What is the Viremia Curve?

A
  • Virus in the blood
  • Infected animals will have this general curve
    • Passive viremia - burst of virus upon inoculation
    • Primary viremia - virus replicates
    • Secondary viremia - virus multiplies in other organs so the viremia is amplified
23
Q

What is Tropism?

A
  • The ability of viruses to infect a specific tissue or type of cell
    • Viremia - blood
    • Hepatotropic - virus can replicate in the liver
    • Enteric - virus can replicate in GI
    • Neurotropic - virus can replicate in nerve tissues
      • Neurovirulent - causes disease in nervous tissue
      • Neuroinvasive - virus can enter the CNS