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2a- Microbiology > Viruses as causes of disease > Flashcards

Viruses as causes of disease Flashcards

1
Q

What is a virus?

A
  • An infectious, obligate, intracellular parasite
  • Comprising genetic material (DNA or RNA) surrounded by a protein coat and/or a membrane
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2
Q

How do viruses replicate?

A

Viruses can only replicate by exploiting the energy and reproductive machinery of cells of higher organisms

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3
Q

What are all the characteristics of viruses?

A

● Non-cellular structure – do not have membranes or any cell organelles
● Consist of an outer protein coat and a strand of nucleic acid, either DNA or RNA
● Come in a variety of shapes
● Do not carry out metabolic reactions on their own – require the organelles and
enzymes of a host to carry out such reactions

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4
Q

Do viruses or bacteria have a cell wall?

A

Bacteria

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5
Q

Do viruses or bacteria have organelles?

A

Bacteria

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6
Q

Do viruses or bacteria have DNA AND RNA?

A

Bacteria (viruses have 1 or the other)

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7
Q

Are viruses or bacteria dependent on host cell?

A

Virus

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8
Q

Are viruses or bacteria alive?

A

Bacteria

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9
Q

Give an example of a non-enveloped virus

A

adenovirus, parvovirus

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10
Q

Give an example of an enveloped virus

A

influenza, HIV

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11
Q

What is a virus envelope made of?

A

Coat of lipid

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12
Q

Describe the steps of virus replication

A
  1. Attachment: virion (virus outside cell), attaches to viral and cell receptors with surface proteins e.g. HIV
  2. Cell entry: uncoating of virion within cell
    - loss of surface proteinsonly
    central viral core carrying the nucleic acid and some associated
    proteins enter host cell
  3. Interaction with host cells: genetic material migrates to cell nucleus to genome of host cell, use cell materials (enzymes, amino acids, nucleotides) for
    their replication
  4. Replication: may localize in nucleus, cytoplasm or both
  5. Assembly: occurs in nucleus, in cytoplasm or at cell membrane
  6. Release: bursting open of cell, or by leaking from the cell over a period of time via budding/exocytosis
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13
Q

What products are made by viral mRNA in translation?

A
  • Structural proteins
  • Viral genome
  • Non-structural proteins eg. enzymes
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14
Q

How do viruses cause disease?

A
  • Direct destruction of host cells
  • Modification of host cell
  • Over-reactivity of immune system
  • Damage through cell proliferation
  • Evasion of host defences
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15
Q

What is an example of a virus that directly destroys host cells?

A
  • poliovirus → host cell lysis and death after viral replication period of 4 hours
    • Neurone cells → paralysis
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16
Q

What is an example of a virus that modifies host cells?

A
  • rotavirus → atrophies villi and flattens epithelial cells
    • Rotavirus causes diarrhoea in young children
      • decreases small intestine SA
      • nutrients including sugar not absorbed
      • hyperosmotic state
      • profuse diarrhoea
17
Q

What is an example of a virus that triggers an over reaction of the immune system?

A
  • hepatitis B
    • infects liver cells by binding to MHC class 1 receptor which triggers cytotoxic T lymphocytes to kill hepatocyte
      • Jaundice
      • Pale stool
      • Dark urine
      • RUQ pain
      • Fever + malaise
      • Itching
18
Q

What is an example of a virus that damages through cell proliferation?

A

human papillomavirus → cervical cancer
- causes dysplasia and neoplasia → metastatic and local spread

19
Q

What are 2 categories of evasion of host defences?

A

Cellular level
Molecular level

20
Q

What are cellular level evasion mechanisms?

A

Latency
Cell-cell spread

21
Q

What is latency?

A

virus able to lie dormant in certain host cells and react in the future

22
Q

What is varicella zoster virus’ primary and secondary infection?

A

Chickenpox
Shingles (herpes zoster)

23
Q

Where do HSV (herpes simplex virus) 1+2 and VZV (varicella zoster virus) lay dormant?

A

In nerve root ganglion

24
Q

Where do EBV and HHV-8 (human herpes virus) lay dormant?

A

Lymphoid cells

25
Q

Where do HHV-6, HHV-7 (human herpes virus) and CMV (Cytomegalovirus) lay dormant?

A

Myeloid cells

26
Q

Give an example of a virus that spreads cell-cell

A

measles, HIV

27
Q

What are molecular level evasion mechanisms?

A
  • Antigenic variability/drift
  • Prevention of host cell apoptosis
  • Downregulation of interferon and other intracellular host defence proteins
  • Interference with host cell antigen processing pathways
28
Q

What does antigenic variability mean?

A

Virus changes structure eg. Flu virus changes every year

29
Q

Give an example of a virus that prevents host cell apoptosis

A

eg. hepesviridae, EBV
EBV can infect lymphoid cells and stop lymphoid cells to die → lymphoma

30
Q

What does downregulation of interferon and other intracellular host defence proteins lead to?

A

Neighbouring cells become susceptible to infection

31
Q

What does Interference with host cell antigen processing pathways lead to?

A

Can’t present abnormal antigen to immune system
eg. herpesviridae, measles, HIV

2a- Microbiology (14 decks)

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