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Virology > Lecture 12 - Pathogenesis of Viral Infections I > Flashcards

Lecture 12 - Pathogenesis of Viral Infections I Flashcards

1
Q

Proportion of the population infected with a herpesvirus

A

98%

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2
Q

Why does most contact with viruses not result in symptoms?
1)
2)
3)

A

1) Particles don’t find a cell to infect
2) Particles are destroyed or inactivated as they enter the host
3) Infections don’t progress beyond one or two host cells

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3
Q

How can viral sensitivity to heat, drying or sunlight (UV) be overcome?

A

Produce a large number of viral particles

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4
Q

How can viruses avoid contact with the outside environment?

A 
Insect vectors (arboviruses)
Transfer via body fluids.  Not outside host for long
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5
Q

What must a virus do to cause infection?
1)
2)
3)

A

1) Gain entry to body
2) Multiply and spread
3) Target appropriate organ

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6
Q

How can a virus be maintained in nature?
1)
2)
3)

A

1) Shed into the environment
2) Taken up by an arthropod vector or needle
3) Passed congenially (mother to foetus transmission)

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7
Q

Example of a systemic infection

A

Polio.

Enters via faecal/oral route, spreads to CNS

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8
Q

Example of a local infection

A

Influenza.

Enters, replicates, is transmitted from respiratory tract

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9
Q

What determines the length of infection?

A

Immune response of the host

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10
Q

Tropism of a virus

A

Anatomical localisation of a virus

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11
Q

Does the human body present many ways for a virus to enter?

A

No. A limited spectrum of entry sites is provided

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12
Q 
Viruses transmitted to the skin via mechanical trauma
1)
2)
3)
4)
5)
A

1) HPV
2) HIV
3) HSV
4) HBV
5) Poxvirus

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13
Q

Viruses transmitted by injection

A

HBV, HIV

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14
Q

Virus transmitted by bite of an infected animal

A

Rabiesvirus

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15
Q

General behaviour of viruses that infect via the skin

A

Don’t multiply locally, but migrate to other tissues.

EG: HBV, arboviruses enter bloodstream. Rabiesvirus migrates along nerves

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16
Q

Most important site of viral entry

A

Respiratory tract

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17
Q

How do viruses enter the respiratory tract

A

Via aerosol inhalation or mechanical transmission of infected nasal secretions

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18
Q

Sites of virus deposition by droplet size
1)
2)
3)

A

1) Over 10 micrometers - Lodge in nose
2) Between 5-10 micrometers - Lodge in airways
3) Under 5 micrometers - Enter alveoli

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19
Q 
Barriers to infection of the respiratory tract
1)
2)
3)
4)
5)
A

1) Mucus
2) Cilia
3) Alveolar macrophages
4) Temperature gradient
5) IgA

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20
Q

How do viruses infect the respiratory tract?

A

Bind to receptors on epithelial cells

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21
Q

Amount of mucus produced per day by a healthy person

A

20-200mL per day in nose and lungs

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22
Q

How fast does the muco-ciliary elevator move liquid from lungs to oesophagus?

A

~1cm/minute

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23
Q 
Viruses that can infect the LRT
1)
2)
3)
4)
A

1) Parainfluenza virus
2) Respiratory syncitial virus
3) Influenza virus
4) Adenovirus

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24
Q 
Viruses that can infect the URT
1)
2)
3)
4)
5)
6)
7)
A

1) Rhinovirus
2) Parainfluenzavirus
3) Respiratory syncitial virus
4) Influenza virus
5) Adenovirus
6) Herpes simplex virus
7) EBV

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25
Q

Hepatitis that can be sexually transmitted

A

HBV

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26
Q

Viruses that cause local GIT infection

A

Rotavirus, coronavirus, adenovirus

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27
Q

Viruses that enter via the GIT to cause systemic infection

A

Enteroviruses, hepatits A

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28
Q

Virus survival requirements if infecting the GIT

A

Acid stability
Resistance to bile salts (basic)
Resistance to inactivation by proteolytic enzymes (in the case of reoviruses, proteolytic cleavage is necessary)

29
Q

Cell often used by viruses to infect the small intestine

A

M cells

30
Q

Only enveloped viruses that can infect the GIT

A

Coronaviruses.

Can be protected from acid by association with milk products

31
Q

How can a virus infect GIT if it lacks receptors for epithelial cells?

A

HIV, Hep B can infect anal route via abrasions in epithelium

32
Q

Viral spread beyond site of infection

A

Disseminated

33
Q

Viral spread beyond site of infection, affecting multiple organs

A

Systemic

34
Q

Examples of local respiratory viruses

A

Influenza, rhinoviruses, respiratory syncitia virus

35
Q

Example of local dermatological virus

A

HPV

36
Q

Example of local GIT virus

A

Rotavirus

37
Q

How can viruses target whether to become local or systemic?

A

Target viral budding to apical or basal surface of host cell.
This might occur via viral glycoproteins.

38
Q

Viremia

A

Presence of viral particles in the blood

39
Q

Types of viremia

A

Passive viremia - Viral particles introduced to blood without viral replication at the site of entry (EG: injection, animal bite)

Active viremia - Presence of newly-synthesised virions in blood

40
Q

Where can viruses be during viremia?

A

Free in blood, or within infected cells in blood

41
Q

Primary and secondary viremia

A

Primary - Released from infected cells at the site of entry. Lower viral titres.

Secondary - Virus has infected a different target organ to the site of entry (often the spleen or liver). Larger viral titres, more prolonged viremia.

42
Q

How is viremia in plasma neutralised?

A

Neutralised by antibodies, removed by macrophages

43
Q

How long does it take for the body to control viremia free in the plasma?

A

1-2 weeks for a neutralising antibody response

44
Q

Examples of viruses causing cell-associated viremia

A

Measles
HIV
Measles and HIV spread in monocytes. HIV spread in CD4+ T cells

45
Q

Days after infection that primary viremia can occur

A

~2 days

46
Q

Days after infection that secondary viremia can occur

A

~4-14 days

47
Q

Stages of viremia in mousepox

A

Primary viremia after two days, replication occurs in skin, regional lymph nodes

Secondary viremia after five days. Replication in spleen and liver.

48
Q

Haematogenous spread

A

Epithelium at body surface drains into lymphatic capillary.
This drains to lymph node, which drains to venous system

49
Q 
Different strategies of tissue invasion from the blood
1)
2)
3)
4)
A

1) Some viruses can infect endothelial cells in blood vessels, infect tissues from the blood
2) Transport across endothelial cells via transcytosis
3) Virus can infect monocytes or lymphocytes, which can cross from blood into tissues
4) Some tissues aren’t joined via tight junctions. EG: mumps moves between cells of chorioid plexus from blood into the brain

50
Q 
How do viruses spread neurally?
1)
2)
3)
4)
5)
A

1) Via peripheral nerves (EG: HSV, varicella, rabies)
2) Uncoated nucleocapsid is carried passively along axons or dendrites
3) Virus multiplies in nerve body. Progeny can cross synaptic junction, infect CNS
4) Protected from CD8+ attack, as neurons lack MHCI
5) Some viruses enter directly from blood

51
Q 
Rabiesvirus neural spread
1)
2)
3)
4)
5)
A

1) Replicates at site of infection (often myocytes) until enough viral particles come into contact with sensory or motor nerve cells
2) Virus enters axons where they aren’t myelinated
3) Move to neuron nucleus via retrograde axoplasmic flow
4) Rabies reaches spinal cord. Clinical rabies occurs when neuronal dysfunction begins.
5) Virus travels along peripheral nerves via anteretrograde axoplasmic flow to salivary glands.

52
Q

How quickly does rabies virus travel along axons?

A

Slowly.

~10-20mm/day

53
Q

Virus that travels from a reservoir to epithelium via anteretrograde transport

A

Herpesvirus

54
Q

Spread of varicella zoster (herpesviridae)

A

Day 0) Infection of conjunctiva and URT
- Viral replication in local lymph nodes
Day 4-6) Primary viremia in bloodstream
-Further replication in liver and spleen. Secondary viremia/
Day 10) Infection of skin, vesicular rash

55
Q

Virus that uses both viremia and neural spread

A

Variacella zoster.
Viremia from replication in lymph nodes, spleen, liver.
Dormancy in dorsal root ganglia

56
Q

Viruses that kill foetuses

A

Cytocidal viruses

57
Q

Viruses that result in abnormalities of foetuses

A

Non-cytocidal viruses

58
Q

Viruses that can infect a baby at birth

A

1) HSV, varicella, CMV (infected birth canal)

2) Coxsackie B (faecal contamination)

59
Q

Spread of viruses that cause acute respiratory disease

A

High titres shed for a short period (~1 week). Influenza, rhinovirus

60
Q

Time of peak infectiousness of measles

A

Prior to onset of rash

61
Q

Places from which viruses can be excreted in faeces

A

From epithelial cells lining intestinal tract (rotavirus)

From the liver via the bile duct (Hep A)

62
Q

How is HPV spread?

A

Only from the top layer of infected skin. Transmitted via mechanical contact. Blood from wart has very high viral titre.

63
Q

How is varicella spread?

A

Shed from virus-filled vesicles.

Can be spread from respiratory tract (aerosolised)

64
Q

Is the measles rash infectious?

A

No

65
Q

Which viruses are normally spread via blood?

A

Viruses that result in persistent viremia

66
Q

Why does direct human-human or human-arthropod-human transmission not often occur with arboviruses?

A

Levels of virus in the blood are too low

67
Q

How is CMV secreted?

A

Urine, saliva, tears, breast milk, semen, cervical secretions

68
Q

How is EBV spread?

A

Saliva

69
Q

How is HIV transmitted?

A

Milk, semen, cervical secretions, blood

Virology (29 decks)

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