Flashcards in Diagnosis FIV and FeLV Deck (15)
What do nearly all diagnostic tests test for?
occasionally cell mediated e.g. TB
What to remember about FIV and FeLV diagnostic tests?
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
List examples of FIV/ FeLV diagnostic tests
• In house immunodiffusion / immunochromatography (lateral flow)
• Western blot
• PCR (looking for DNA, i.e provirus)
• RT-PCR (viral RNA genome NOT provirus)
With in house FeLV and FIV what are the tests testing for?
With in house FeLV what are the tests testing for?
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
With in house FIV what are the tests testing for?
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
Where is FIV virus prodominantly shed
How does lateral flow device work: FeLV
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
Broadly what are 2 methods to test for virus?
principle 2 ways of looking for viruses - immune response or looking for organism itself
Lateral flow for FIV
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
Proportion of true positives picked up by the test
Proportion of true negatives picked up by the test
Define Positive Predictive value
proportion of true positive results
Define negative predictive value
Proportion of true negative results