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Feline Immunodeficiency Virus (view source)
Revision as of 13:33, 27 August 2010
, 13:33, 27 August 2010→Laboratory Tests
===Laboratory Tests===
===Laboratory Tests===
**False positives occur, particularly in the presence of maternal Ab
The standard in-practice diagnostic tests detect serum
*Positives can be confirmed by lab work (Western blotting)
antibodies to FIV using a variety of commercially
available laboratory kits. Some test kits detect antibody
to the core protein p24, whereas others detect antibody
to the envelope protein gp4l. Non-haemolysed
plasma or serum is most reliable for use in these tests.
The use of whole anticoagulated blood is discouraged
since this can make the interpretation of colour changes
difficult and hence increase the risk of false positive
results.
INTERPRETING A POSITIVE RESULT
A positive test result is found in three situations:
* PERSISTENTLY INFECTED CATS. FIV antibodies are
associated with lifelong infection with this virus.
* KITTENS BORN TO AN FIV-POSITIVE QUEEN. Passive
transfer of antibodies occurs via the milk, with the
result that maternally derived antibodies may be
detected when kittens are blood tested for FIV antibodies.
Although all of the kittens born to a queen infected
with FIV may be antibody positive, the virus itself is
usually only passed on to a maximum of one-third of the
kittens in a litter. Maternally derived antibodies may persist
for up to four months and it may be a further two
months before infected kittens seroconvert. It is therefore
recommended that kittens born to FIV-infected
queens are not antibody tested until they are at least six
months old.
* FALSE POSITIVE RESULT. No test is 100 per cent accurate
and so the clinical signs and background of the cat
should be taken into account when assessing test results.
Generally, a specificity of around 98 per cent is recognised
with practice test kits.
Weak positive test results are usually seen when there
is non-specific binding causing a partial colour change.
These should be interpreted as equivocal results and the
cat should be retested using a different test.
INTERPRETING A NEGATIVE RESULT
Negative results indicate one of three possibilities:
* THE CAT IS NOT INFECTED WITH FIV.
* THE CAT IS FIV INFECTED BUT HAS ANTIBODIES NOT
DETECTABLE BY THE TEST USED.
* THE CAT IS FIV INFECTED BUT THERE ARE NO ANTIBODIES
PRESENT. This may be the case in the early stages
of infection (less than two months post-infection). If the
cat is known to have recently been at risk, for example
recently bitten by an FIV-positive cat, it should be retested
six to eight weeks later. In some cats, there is a failure
to mount an antibody response to the virus, meaning that
these animals never seroconvert and so are not identifiable
by these tests. Up to 15 per cent of FIV-infected
cats may be seronegative.
===Pathology===
===Pathology===