viral properties and disease

Question 1

basis for classification of viruses

Answer 1

type of genome (Baltimore classification): DNA (ss/ds) or RNA (+ve/-ve/ds), which cycle do they follow - e.g. retrovirus RNA genome but go through DNA intermediate to make more RNA

Question 2

2 types of virus morphology

Answer 2

enveloped, non-enveloped

Question 3

characteristics of non-enveloped viruses

Answer 3

protein capsid, more symmetrical

Question 4

examples of non-enveloped viruses

Answer 4

adeno, picorn, calici

Question 5

characteristics of enveloped viruses

Answer 5

lipid envelope derived from host membrane, pleiomorphic (various shapes e.g. measles or typical shape e.g. ebola)

Question 6

example of a virus which is a combination of capsid and envelope

Answer 6

herpes

Question 7

ways viruses are named

Answer 7

disease, discovered (name/place), part of body affected, mode of transmission

Question 8

3 consequences of RNA retroviruses

Answer 8

use own polymerase to replicate so high mutation rate as lack proof reading capacity; limited in size as RNA unstable; often complicated coding strategies to encode more proteins

Question 9

3 consequences of DNA viruses

Answer 9

can be large as more stable; space for accessory genes (e.g. to suppress immune system; can be lost in culture, producing vaccines); segmented genome allows opportunity to pick up new genes and evolve

Question 10

criteria for investigating viruses in labs

Answer 10

must be grown in host cell (which must previously have been grown in lab)

Question 11

investigating viruses in labs: how do cells die from virus

Answer 11

cytopathic effect: death of cell due to viral effect, normally through lysing by shutting down host protein synthesis or accumulation of viral proteins; hole in cell layer visible if stained

Question 12

investigating viruses in labs: what is a plaque

Answer 12

result of an individual virus infecting one cell then infecting others

Question 13

investigating viruses in labs: what does number of plaques correspond to

Answer 13

number of viruses, so used to find how much virus in patient using plaque assay

Question 14

investigating viruses in labs: what is a plaque assay

Answer 14

sample containing virus using serial 10 fold dilutions: known volume put on susceptible cells, then plaques counted and multiply back due to serial dilution

Question 15

investigating viruses in labs: what does a plaque assay determine

Answer 15

effectivity of antiviral drugs

Question 16

what can also occur instead of a plaque forming

Answer 16

big bundle of cells fused together - syncytia (e.g. HIV - glycoproteins interact with receptor on opposite cell)

Question 17

how are infected cells immunostained

Answer 17

sample inoculated onto cell and wait until produces virus-unique proteins, then use antibodies to detect

Question 18

3 phases of viral infection

Answer 18

eclipse phase (decreases), logarithmic phase (increases), cell death

Question 19

single step growth kinetics of virus graph

Answer 19

graph

Question 20

5 methods of viral diagnosis

Answer 20

viral genome (e.g. PCR), viral antigen (e.g. IFA, ELISA), viral particles (e.g. electron microscopy or haemagglutination assay), virus cytopathic effect in cultured cells, antibodies to virus after event (e.g. serology)

Question 21

what does choice of viral diagnosis method depend on

Answer 21

source of specimen, purpose, who and where, what stage disease is

Question 22

how are viruses propagated in a lab

Answer 22

passage viruses using permissive cells (continuous lines of transformed cell cultures)

Question 23

how does attenuation occur in propagating viruses and what was this used for

Answer 23

virus may mutate and adapt to new host, which was basis of past vaccines

Question 24

how can virus propagation be manipulated to create new viruses

Answer 24

small genomes can be synthesised, and new viruses can be produced by reverse genetics