Virus Quantification

Question 1

virus quantification

Answer 1

counts the number of viruses in a specific volume to determine the virus concentration

Question 2

virus titer

Answer 2

lowest concentration of virus that still infects cells. Number of infectious units per ml of the sample/solution

Question 3

biological quantification tests

Answer 3

depends on a virus particle initiating a successful replication cycle
plaque assay
pock assay
various endpoint titration methods

Question 4

physical quantification tests

Answer 4

do not depend on any biological activity of the virus particle
electron microscopic particle counts
hemagglutination
immunological assay, ELISA
quantitative PCR assay
flow cytometry

Question 5

direct particle count by transmission electron microscope (TEM)
why is it not generally performed

Answer 5

expensive, required trained staff, changes of error are high

Question 6

virus counter 2100

Answer 6

specialized flow cytometry, each sample is stained with two different fluorescent dyes, one for nucleic acid, and the other for protein. The particles are analyzed as they flow through a laser beam

Question 7

hemagglutination assay

Answer 7

if antibodies are present, they stick to RBCs and cause mat formation. if antibodies are not present, the RBCs settle to the bottle forming a button

Question 8

HA titer

Answer 8

the inverse of the greatest dilution that completely agglutinates the RBCs

Question 9

high performance liquid chromatrophy (HPLC)

Answer 9

the concentrations of specific viral antigens may be quantified through UV analysis of fractions generated during this test. Gives indirect idea of virus concentration

Question 10

single radial immunodiffusion (SRID)

Answer 10

radial diffusion of purified viral antigens (standards) and viral particles through agarose gel seeded with polyclonal antisera against a viral antigen

Question 11

plaque

Answer 11

a circular zone of necrotic cells surrounded by viable cells in a biological assay

Question 12

monolayer plaque assay

Answer 12

it is a functional measurement, and has no relation to the actual number of viruses. Units= PFU

Question 13

virus replication cycle (10 steps)

Answer 13

attachment, penetration, uncoating, translation of early mRNA, translation of early proteins, replication of viral DNA, transcription of late mRNA, translation of late proteins, assembly of virions, release

Question 14

determining titer (equation)

Answer 14

average plaque count x reciprocal of dilution selected

Question 15

pock

Answer 15

necrotic region. Unit= pock forming units

Question 16

transformation assay

Answer 16

quantitative determination of titers of oncogenic viruses. transformed cells lose contact inhibition and become heaped upon one another

Question 17

quantal assay

Answer 17

measures presence of absence of infection

Question 18

endpoint

Answer 18

virus dilution that affects 50% of the test subjects

Question 19

tissue culture infectivity dose 50

Answer 19

dose in which 50% of the tissue dies

Question 20

lethal dose 50

Answer 20

the dose that kills 50% of the subjects

Question 21

embryo lethal dose 50

Answer 21

dose in which 50% of the embryos die

Question 22

paralytic dose 50

Answer 22

dose that causes paralysis in 50% of the subjects

Question 23

TCID50

Answer 23

the tissue culture infectious dose which will infect 50% of the cell monolayers challenged with the defined inoculum

Question 24

multiplicity of infection (MOI)

Answer 24

the average number of virus particles infecting each cell

Question 25

equation for TCID50

Answer 25

[(%infected above 50%) - (50%)] / [(%infected above 50%) - (%infected below 50%)]