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MM- Viruses > MM0 > Flashcards

MM0 Flashcards

1
Q

Viruses were first described as?

A

Filterable agents

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2
Q

Mimivirus genome is how large?

A

1.2 million base pairs

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3
Q

What virus suggested that viruses may represent the fourth domain of life?

A

Mimivirus

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4
Q

Why did mimivirus suggest viruses may represent the fourth domain of life?

A
  • Genome larger than some bacteria
  • Larger than Rickettsia bacterial species
  • Contained genes associated with translation
  • Genes encoding proteins for amino/nucleotide synthesis, does not rely on the host for these pathways
  • Can be infected by virophages including Sputnik
  • Although, does not encode a ribosome
  • Also undergoes assembly of progeny instead of division
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5
Q

What is pathogenesis?

A

Pathogenesis is a qualitative description of disease

It includes the biological mechanisms a pathogen uses to cause disease and the ability of a pathogen to cause disease

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6
Q

What is virulence?

A

It is quantitative and relative (non-scalar)

It is the extent of disease caused

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7
Q

How can virulence be measured?

A

Morbidity
Mortality
Temperature during fever etc…

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8
Q

Before the advent of tissue culture how were viruses studied?

A

In vivo passage

In ovo passage

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9
Q

How can the number of infectious particles present be measured?

A

Plaque assays

End point assays

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10
Q

Which assay was used first?

A

End-point essay

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11
Q

What is the end point?

A

The dilution at which 50% of cells/animals are infected

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12
Q

Why are end-point assays still used today?

A

For viruses that do not produce plaques

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13
Q

Describe how a plaque assay works?

A

10 fold dilutions
Inoculate a tissue monolayer with aliquots
Allow time for the viruses to attach
Place agar layer on top to restrict infection of viruses to neighbouring cells only
Use a dye to colour the cells, areas of cell death are represented by a colourless plaque

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14
Q

What is the pfu?

A

Plaque forming unit

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15
Q

How can the titre of the original virus stock be calculated?

A

Using the number of plaque forming units obtained

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16
Q

What is the particle/pfu ratio?

A

When using an electron microscope particles of viruses can be identified. If this is higher than the pfu it means that many of the virus particles assembled were non-infectious e.g. did not contain viral genome/ functioning viral genome

17
Q

What does MOI stand for?

A

Multiplicity of infection

18
Q

What is moi?

A

The number of viral particles to cells present

19
Q

MOI of 1?

A

There is one viral particle per cell present

20
Q

What is virulence?

A

Virulence is non-scalar (relative). It is a quantitative measure of the extent of disease.

21
Q

How can virulence be measured?

A

Virulence can be measured by:

  • Mortality
  • Morbidity
  • Temperature change (fever)
  • Weightloss
22
Q

What is pathogenicity?

A

Pathogenicity is a qualitative description of the ability of a pathogen to cause disease. Includes the biological mechanisms by which the pathogen causes disease

23
Q

What were the two strains of smallpox?

A

Variola major and variola minor

24
Q

Which strain of smallpox was more virulent?

A

Variola major was more virulent as it had a fatality rate of 20%, variola minor only had a fatality rate of around 1-2%

25
Q

Describe viruses which result in acute infection?

A

Influenza
Ebola
Smallpox

26
Q

Describe viruses which have a latent lifestyle?

A

Herpes virus

27
Q

Describe viruses which have a chronic lifestyle:

A

HBV
HCV
HIV

28
Q

Example of a localised infection caused by a virus?

A

HPV infection is restricted to the genitals

29
Q

Example of a virus capable of systemic infection and their route of spread?

A

Rabies spreads via the nerves
HSV can spread via the nerves
Polio can spread via the blood
HIV can spread via the blood

30
Q

What can determine the tropism of a virus?

A

Viral tropism can be determined by the cell receptors- the receptors by which it gains cell entry

31
Q

What determines the tropism of HIV?

A

The presence of the chemokine receptors

Only present on white blood cells which is why it infects these

32
Q

What determines the tropism of HCV?

A

A micro RNA
miRNA-122
This is produced in abundance in hepatocytes
It binds upstream of the IRES in the 5’ UTR and stabilises the genome allowing translation to begin

MM- Viruses (13 decks)

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