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MICR2209 > 12 - Viral Pathogenesis > Flashcards

12 - Viral Pathogenesis Flashcards

1
Q

Requirements for successful infection

A
  • Dose (enough virus)
  • Access to target cells (susceptible, permissive)
  • Absent or insufficient host immunity
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2
Q

Short incubation period

A
  • <1 week
  • Localised infections
  • Arboviruses (viruses transmitted by mozzies)
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3
Q

Medium incubation period

A
  • 7-12 days
  • Generalised infections
  • Measles
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4
Q

Long incubation periods

A
  • Weeks to months
  • Rabies
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5
Q

Very long incubation periods

A
  • Years
  • Usually fatal
  • Prion diseases
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6
Q

Latent

A

Persistence of viral genome in the host cell and periodic virus reactivation

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7
Q

Viral pathogenesis

A

complex interaction between virus and host that results in disease

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8
Q

Viral pathogenesis stages

A
  • Entry and primary replication
  • Viral spread and cell tropism
  • Cell injury and clinical illness
  • Recovery from infection
  • Virus shedding and transmission
  • Host immune response
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9
Q

Pathogenicity

A

the comparison of the severity of disease caused
by different microorganisms

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10
Q

Virulence

A

comparison of the severity of disease caused by
different strains of the same microorganism

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11
Q

Viruses endemic in rodents

A

Hemorrhagic disease viruses (e.g. Lassa, Junin, Sin Nombre)

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12
Q

dead end host

A

Effect host but not transmitted between hosts

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13
Q

Entry through the skin

A
  • Abrasions (HPV)
  • Inoculation with contaminated needles (HIV, Hep B and C)
  • Insect or animal bites (Dengue, rabies)
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14
Q

Entry through mucous membranes

A
  • Respiratory tract (Influenza)
  • Gastrointestinal tract (faecal-oral route, Poliovirus)
  • Conjunctiva (Adenoviruses,)
  • Genital tract (HSV, HIV)
  • Transplacental (congenital, vertical: HSV, Rubella)
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15
Q

Apical release

A

virus does not usually invade
underlying tissues

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16
Q

Basolateral release

A

virus has access to underlying tissues and this may allow systemic spread

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17
Q

Which release causes disseminated infection

A

Release from both apical and basal surfaces

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18
Q
A
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19
Q

Haematogenous spread

A
  • Viruses taken up by the local lymphatic vascular system, replicate in endothelial cells or
    inoculation by a vector bite.
  • Access almost every tissue in the host
20
Q

Viraemia

A

Presence of infectious virus particles in the blood

21
Q

Active viraemia

A

produced by virus replication

22
Q

Passive viraemia

A

virus particles are introduced into the blood without viral replication at the site of entry

23
Q

Secondary viraemia

A

subsequent disseminated
infections, appearance of a high concentration of
infectious virus in the blood

24
Q

Cellular factors of viral invasion of the host

A
  • Presence of appropriate receptors
  • Physical and molecular environment must enable initial replication cycle (temperature, pH)
25
Q

Lysis

A
  • Virus-encoded proteins may shut down synthesis of cell macromolecules
  • accumulation of viral proteins may inhibit host cell function.
  • Cell death is followed by lysis and release of viral particles
26
Q

Syncytium formation

A
  • fusion of an infected cells with neighbouring cells leading to the formation of multinucleate enlarged cells (syncytia)
  • allows viruses to pass from cell to cell, instead of being released via lysis
27
Q

Ananthem

A

Rash on mouth mucosa

28
Q

Vesicular eruptions

A

Viral replication in the skin (herpes)

29
Q

Maculopapular rash

A

destruction of infected cell by cytotoxic T lymphocytes (measles)

30
Q

Purpuric rash

A

Thrombocytopenia (Dengue)

31
Q

Haemorrhagic rash

A

result of disseminated intravascular coagulopathy

32
Q

Disseminated

A

Spread of virus beyond primary site

33
Q

Systemic

A

Infecting many different organs

34
Q

Important target organs of dissemination

A
  • Lungs
  • Liver
    -CNS
35
Q

Lungs

A
  • Most respiratory infections are localised
  • Some are generalised (measles)
36
Q

Liver

A
  • Target for hepatitis viruses
  • Infected during generalised infections (e.g. yellow fiver)
37
Q

CNS

A
  • Access from bloodstream during viraemia (e.g. Polio)
  • Via peripheral nerves (Herpes, Rabies)
38
Q

Dissemination pathway of herpes

A
  1. Virus inoculated
  2. Viral replication in muscle
  3. Virus binds to nicotinic acetylcholine receptors at neuromuscular junction
  4. Virus travels within axons in peripheral nerves (retrograde axonal transport)
  5. Replication in motor neurons of the spinal cord and local dorsal root ganglia and rapid ascent to brain
  6. Infection of brain neurons with neuronal dysfunction
  7. Centrifugal spread along nerves to salivary glands, skin, cornea
39
Q

Aseptic meningitis (not caused by pyogenic bacteria)

A
  • Inflammation of the meninges
  • Viral infection is the most common (enterovirus)
40
Q

Encephalitis

A
  • Inflammation of the brain
  • Headache, confusion, seizures, hallucinations
  • Can be fatal
  • Enterovirus, HSV, rabies, arboviruses
41
Q

Acute flaccid paralysis

A
  • acute onset of flaccid
    paralysis in one or more limbs
  • Caused by anterior horn cell infection with wild or vaccine polio virus
42
Q

What can primary HIV disease lead to

A
  • AIDS Dementia complex (brain)
  • Vacuolar Myelopathy (spinal cord)
  • Peripheral Neuropathy (nerve)
  • Meningitis (acute or chronic)
43
Q

Zika virus

A
  • Spread by mosquitos
  • Most cases asymptomatic, mild flu like symptoms
  • Increased risk of Guillain-Barré Syndrome
  • Vertical transmission causing microcephaly and other congenital brain abnormalities
  • Sexual transmission and blood-transfusion (WHO)
44
Q

Reproduction number (R0)

A
  • The average number of secondary cases generated
    by one primary case in a susceptible community
  • The higher the R0, more persons infected from one
    primary case
45
Q

Viral shedding

A
  • Viruses shed from an infected host can infect new susceptible hosts
  • May be shed from primary site of multiplication or from target organ
  • Healthy individuals may shed viruses continuously (e.g. HSV in saliva)
46
Q
A
47
Q
A

MICR2209 (26 decks)

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