Changes

Once a cat acquires FIV infection, the antibodies created persist for life. This means that an ELISA test at any stage after infection should give a positive result. However, the test has a sensitivity of 98%, and so false positives do occur. Because of this, animals that test positive to an in-house ELISA, should be re-tested using a different test. Laboratories offer an immunoblot (Western blot) to confirm the diagnosis in cats that test ELISA-positive. The problem of using a test that detects anitbodies becomes apparent when it is neccessart to test kittens that are born to an FIV-positive queen. Antibodies against FIV are passively acquired via the milk, and can be detected when an ELISA test is used. This makes it imposible to distinguish animals that have been transplacentally infected with virus and are producing their own antibodies from those which have merely acquired pre-formed anitbodies from their mother. Maternally derived anitbodies can persist for up to 6 months², and so animals testing positive before this age should be restested at 8-12 months old⁵.

Once a cat acquires FIV infection, the antibodies created persist for life. This means that an ELISA test at any stage after infection should give a positive result. However, the test has a sensitivity of 98%, and so false positives do occur. Because of this, animals that test positive to an in-house ELISA, should be re-tested using a different test. Laboratories offer an immunoblot (Western blot) to confirm the diagnosis in cats that test ELISA-positive. The problem of using a test that detects anitbodies becomes apparent when it is neccessart to test kittens that are born to an FIV-positive queen. Antibodies against FIV are passively acquired via the milk, and can be detected when an ELISA test is used. This makes it imposible to distinguish animals that have been transplacentally infected with virus and are producing their own antibodies from those which have merely acquired pre-formed anitbodies from their mother. Maternally derived anitbodies can persist for up to 6 months², and so animals testing positive before this age should be restested at 8-12 months old⁵.

   

   

Negative results can be true negatives. Alternatively, they may arise when the cat is infected with FIV but the antibodies produced are not detectable by the test used. Conversely, the cat may be infected but antibodies are not present, for example in the first two months of infection². Therefore, if clinical signs give a strong suspicion of FIV infection, or the cat is known to be at risk (for example, recently bitten by and infected cat), animals should be retested 6-8 weeks later and use of an immunoblot should be considered. Up to 15% of cats completely fail to ever mount an antibody response against FIV infection. Virus isolation and RT-PCR tests exist that can detect virus rather than antibody, but these are not widely available outside the context of research, and RT-PCR in particular may be unreliable⁵.

Negative results can be true negatives. Alternatively, they may arise when the cat is infected with FIV but the antibodies produced are not detectable by the test used. Conversely, the cat may be infected but antibodies are not present, for example in the first two months of infection². Therefore, if clinical signs give a strong suspicion of FIV infection, or the cat is known to be at risk (for example, recently bitten by and infected cat), animals should be retested 6-8 weeks later and use of an immunoblot should be considered. Up to 15% of cats completely fail to ever mount an antibody response against FIV infection. Virus isolation and RT-PCR tests exist that can detect virus rather than antibody, but these are not widely available outside the context of research, and RT-PCR in particular may be unreliable^{4, 5}.

===Pathology===

===Pathology===