Diagnosis FIV and FeLV

Question 1

What do nearly all diagnostic tests test for?

Answer 1

Ab

occasionally cell mediated e.g. TB

Question 2

What to remember about FIV and FeLV diagnostic tests?

Answer 2

1. There is a lot of choice of tests but none are perfect
2. So if get positive animal, must think test could be wrong
3. The diagnostic tests wither detect immune response or a part of an organism

Question 3

List examples of FIV/ FeLV diagnostic tests

Answer 3

• In house immunodiffusion / immunochromatography (lateral flow)
• IF
• IFAT
• Isolation
• Western blot
• PCR (looking for DNA, i.e provirus)
• RT-PCR (viral RNA genome NOT provirus)

Question 4

With in house FeLV and FIV what are the tests testing for?

Answer 4

FeLV antigen

FIV antibody

Question 5

With in house FeLV what are the tests testing for?

AND whyyyy

Answer 5

FeLV antigen
FIV antibody

FeLV - antigen tested as ONLY persistently infected animals have Ab not latently
Those immune recovered/ latent infection have cleared protein
Vaccination - lot of cats are vaccinated = would detect Ab
Ab levels can fluctuate and could lead to false positives

Question 6

With in house FIV what are the tests testing for?

AND whyyyy

Answer 6

FeLV antigen
FIV antibody

FIV Ab as….. virus isolation is slow and expensive
Virus levels fluctuate in early infection, then v low after short time
No vaccine to interfere with test like with FeLV
Ab levels remain high for most of the infection.
Cats can’t clear infections so Ab equate to infection and virus

Question 7

Where is FIV virus prodominantly shed

Answer 7

saliva

Question 8

How does lateral flow device work: FeLV

Answer 8

1. test measures Antigen (called p27, a viral protein heavily present in blood of infected cats)
2. Plate - particles with a laboratory Ab bound
3. add sample (usually blood) to a well
4. If p27 antigen present then will bind to Ab on plate
5. Liquid diffuses across to TEST RESULT WINDOW where another Ab for p27 is.
6. forms bridge - Ab - P27 antigen - ab
7. concentrates here and forms line/ dot
8. CONTROL WINDOW further along ensures we know If diffusion has or hasn’t worked

Question 9

Broadly what are 2 methods to test for virus?

Answer 9

principle 2 ways of looking for viruses - immune response or looking for organism itself

Question 10

Lateral flow for FIV

Answer 10

same principle as for FeLV just ANTIGEN on plate and Ab in blood

1. Test is Ab in blood if Ab binds to Ag in TEST WINDOW, forming bridge
2. CONTROL window to ensure diffusion occured

Question 11

Define sensitivity

Answer 11

Proportion of true positives picked up by the test

Question 12

DEfine Specificity

Answer 12

Proportion of true negatives picked up by the test

Question 13

Define Positive Predictive value

Answer 13

proportion of true positive results

Question 14

Define negative predictive value

Answer 14

Proportion of true negative results

Question 15

Take home message with FIV adn FeLV testing

Answer 15

• Take home message - in low prevalence populations (typical) ALL POSITIVE IN-HOUSE TESTS MUST BE REPEATED BY AN INDEPENDENT TEST