MM0 Flashcards
Viruses were first described as?
Filterable agents
Mimivirus genome is how large?
1.2 million base pairs
What virus suggested that viruses may represent the fourth domain of life?
Mimivirus
Why did mimivirus suggest viruses may represent the fourth domain of life?
- 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
What is pathogenesis?
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
What is virulence?
It is quantitative and relative (non-scalar)
It is the extent of disease caused
How can virulence be measured?
Morbidity
Mortality
Temperature during fever etc…
Before the advent of tissue culture how were viruses studied?
In vivo passage
In ovo passage
How can the number of infectious particles present be measured?
Plaque assays
End point assays
Which assay was used first?
End-point essay
What is the end point?
The dilution at which 50% of cells/animals are infected
Why are end-point assays still used today?
For viruses that do not produce plaques
Describe how a plaque assay works?
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
What is the pfu?
Plaque forming unit
How can the titre of the original virus stock be calculated?
Using the number of plaque forming units obtained
What is the particle/pfu ratio?
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
What does MOI stand for?
Multiplicity of infection
What is moi?
The number of viral particles to cells present
MOI of 1?
There is one viral particle per cell present
What is virulence?
Virulence is non-scalar (relative). It is a quantitative measure of the extent of disease.
How can virulence be measured?
Virulence can be measured by:
- Mortality
- Morbidity
- Temperature change (fever)
- Weightloss
What is pathogenicity?
Pathogenicity is a qualitative description of the ability of a pathogen to cause disease. Includes the biological mechanisms by which the pathogen causes disease
What were the two strains of smallpox?
Variola major and variola minor
Which strain of smallpox was more virulent?
Variola major was more virulent as it had a fatality rate of 20%, variola minor only had a fatality rate of around 1-2%
Describe viruses which result in acute infection?
Influenza
Ebola
Smallpox
Describe viruses which have a latent lifestyle?
Herpes virus
Describe viruses which have a chronic lifestyle:
HBV
HCV
HIV
Example of a localised infection caused by a virus?
HPV infection is restricted to the genitals
Example of a virus capable of systemic infection and their route of spread?
Rabies spreads via the nerves
HSV can spread via the nerves
Polio can spread via the blood
HIV can spread via the blood
What can determine the tropism of a virus?
Viral tropism can be determined by the cell receptors- the receptors by which it gains cell entry
What determines the tropism of HIV?
The presence of the chemokine receptors
Only present on white blood cells which is why it infects these
What determines the tropism of HCV?
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
