Unit 4 - Diagnostics

Question 1

What tests detect antibody?

Answer 1

ELISA, SN, IFA

Question 2

What tests detect agent?

Answer 2

PCR, sequencing, culture/VI, IFA, IHC

Question 3

What is diagnostic sensitivity?

Answer 3

The ability to correctly identify a positive from a group of known positives

Question 4

What is diagnostic specificity?

Answer 4

Ability to correctly identify a negative from a group of known negative samples

Question 5

What factors can affect testing?

Answer 5

Maternal protection, vaccination history (killed, MLV, date, dose), and sentinel animals

Question 6

How is the positive predictive value calculated?

Answer 6

True positives/ (True positives +false positives)

Question 7

How is the negative predictive value calculated?

Answer 7

True negatives / (True negative + false negatives)

Question 8

What does the positive predictive value assess?

Answer 8

The reliability of a positive test

Question 9

What does the negative predictive value assess?

Answer 9

The reliability of a negative test

Question 10

How is sensitivity calculated?

Answer 10

True positive/ (True positive + False negative)

Question 11

How is specificity calculated?

Answer 11

True negative / (True negative + false positive)

Question 12

Why/When is pooling of samples okay?

Answer 12

Decrease costs
Slight loss of analytical sensitivity
Real time PCR - amplification
1 Ct = 2 fold replication
PCR expect low Ct (high concentration)

Question 13

Why/When is pooling of samples not okay?

Answer 13

Concentration dependent
ELISAs
PCR expect high Ct (low concentration)

Question 14

T/F: Cutoff points are not black and white

Answer 14

True

Question 15

Timing of testing determines what you _______ find.

Answer 15

could

Question 16

What are the phases of the ‘antibody responses against antigen’ curve?

Answer 16

Lag phase
Log phase
Plateau phase
Decline phase

Question 17

T/F: Different assays have different advantages and disadvantages.

Answer 17

True

Question 18

What is needed in order to perform virus isolation properly?

Answer 18

You need to know the target virus for the growth medium

Question 19

What are the pros and cons to PCR?

Answer 19

Pros: quick, +/- quantify the amount of virus, defined window for success, can pool samples
Cons: Requires proper primers, moderate cost

Question 20

What are the pros and cons to sequencing?

Answer 20

Pros: Are there any…?
Cons: Takes time, not cheap, shows only part of the virus, difficult to interpret

Question 21

T/F: Necropsy is a diagnostic tool too.

Answer 21

True