Viral Properties

Question 1

define virus

what does the genome comprise of?

Answer 1

infectious obligate IC parasites

DNA or RNA

Question 2

what does Koch’s postulates say about proving a virus causes disease?

Answer 2

microorganism must be found in large numbers in diseased animals but nor healthy
microorganism must be isolated and grown outside the diseased animal in a pure cultures
when injected into healthy animals must cause same disease
suspected microorganism recovered from experimental host and found to be identical

Question 3

what is the average virus size?

Answer 3

100nm

Question 4

summarise virus morphology

give examples of each

Answer 4

non-enveloped
-protein capsid
-symmetrical
e.g. adenovirus, picornavirus, calicivirus
enveloped
-proteins around genome
-lipid enveloper derived from host membrane
-pleomorphic 
e.g. ebola virus 
combination of capsid and envelope
e.g. herpes

Question 5

how is a virus named?

Answer 5

the disease, person/place who/where discovered it, body part affected, way it spreads

Question 6

how are viruses classified?

Answer 6

genome type

Question 7

list the genome types of viruses

Answer 7

dsDNA, ssDNA
positive strand RNA
negative strand RNA
dsRNA

Question 8

explain +RNA and -RNA

Answer 8

+RNA is sense strand so immediately translated

-RNA is antisense strand so is transcribed back to sense using viral proteins and enzymes

Question 9

what are the consequences of viral genome type?

Answer 9

• RNA virus/retrovirus use self polymerase to replicate and lack proofreading = high mutation
• RNA viral genomes limited in size due to lack of stability and have complex coding strategies
• DNA viruses have large genomes so have accessory genes that modify the immune response
• segmented genome allow easy recombination

Question 10

how are viruses grown in the lab?

Answer 10

cells grown in lab and infected by cell

Question 11

what is the cytopathic effect?

Answer 11

death of a cell as a result of being infected by a virus

Question 12

what is CPE due to?

Answer 12

virus taking over genetic machinery so cell can’t produce proteins need to survive, apoptosis

Question 13

what do viruses do to cell monolayers? why?

Answer 13

form plaques

due to cell death

Question 14

what are plaques? what are the uses?

Answer 14

the result of an individual virus infecting one cell and then infecting other cells
-find out how much virus is in the patient using plaque assay

Question 15

summarise the plaque assay process

Answer 15

sample taken from infected patient
make serial 10 fold dilutions
known volume of dilutions taken and put into susceptible cells
plaques on susceptible cell show how may viruses are in dilution

Question 16

what is syncytia formation?

Answer 16

viruses that don’t make plaques have surface proteins that can fuse at neutral pH and often fuse cells together

Question 17

what is immunostaining infected cells?

Answer 17

inoculate their sample onto a cell and wait for the cell to start producing a protein unique to the virus
antibody added that detects protein

Question 18

what is single step growth kinetics of virus?

Answer 18

virus put on cells and sample collected and titrated at specific times
EARLY/ECLIPSE phase - no virus as entered cell
LOGARITHMIC phase - virus makes new copies that exit cells and become detectable
CELL DEATH phase - tails off as cells die

Question 19

list the viral diagnosis types

Answer 19

detecting:
viral genome - PCR
viral antigen - IFA, ELISA
viral particles - EM, HA
viral cytopathic effect in cultured cells - viral isolation
antibodies to virus - serology

Question 20

explain propagating viruses

Answer 20

viruses can be passaged in labs by providing permissive cells
viruses accumulate mutations that adapt them to new host
leads to attenuation snd is basis for vaccine generation

Question 21

define attenuation

Answer 21

changing an infectious agent so it is less virulent and harmful

Question 22

how are viruses manipulated?

Answer 22

genomes are small so can be synthesised
introduced to permissive cells they direct synthesis of their components
allows reverse genetics and creation of viruses with engineered mutations