Jenny,
I haven't heard back from my specialty vet yet. Something tells me they don't have a definitive answer, probably no one does. It was so kind of you to break down what they are saying on the website I found. You've got me thinking, if Sally tests neg on her second test, it is not worth taking any chances, no matter what. If Sally really is negative, she as a kitten, is too vulnerable to this insidious disease. It's just not worth exposing her if she can find a loving home in a negative environment. I don't know which test the rescue is planning to use for the re-test. I will strongly recommend an IFA vs another ELISA. I have no real influence here, but I'll throw my two cents in and pray for the highest good.
Thank you again,
Nina

Mon, 04 Oct 2010 10:43:01 -0700

Nina,

I haven't done a recent search on the persistence of felv but judging from
the quote you had in your email, I can tell you what it sounds like they
think.

PCR is a very senstive test for DNA or RNA.  Basically you have a probe that
attaches to the DNA or RNA of interest.  You then amplify this region over
and over again until you can detect it.  Molecular (genetic) tests are
somewhat new and so their interpretation is not always understood.  By
having a positive PCR test, the only thing that you can say is that the
portion of DNA you put in a probe for is present in your sample.  This DNA
does not mean there is a virus present in your blood (by virus I mean a
particle that has DNA or RNA that is surrounded by a capsule - this particle
is infectious).  It only means that the DNA is present.  Viral DNA implants
itself into your cat's DNA - when it is sitting there, it is not doing any
damage.  When it starts to proliferate, it uses your cats own cells to make
more of it's particles (DNA surrounded by a capsule).  It makes thousands of
viral particles that then rupture the cat's cells and they go on to infect
other cells.

What I am trying to say is that if you can detect felv DNA or RNA -  it can
either be active viral particles or it can be the single strand of DNA in
your cat's cells just doing nothing.  felv is a retrovirus, however, so when
in it's particle form it  should have RNA rather than DNA.  They change the
RNA to DNA and then implant in your cat's cells DNA.  They could potentially
use this difference as a way to differentiate between viral particles and
latent viral DNA in your cat's cells.  I don't know if this has been looked
at yet.

When they talk about antigen negative, that is basically a negative snap
test or IFA.  Both of these tests are looking for specific antigens on the
felv capsule.  If it comes up positive, that mean that the test is detecting
presence of the viral capsule - this means the viral particles are present.

I really hope this makes sense.

If it were me and the second test came back negative (are you doing a repeat
snap (ELISA) or IFA - I would be more inclined to believe an IFA)  my guess
would be that you had an initial false positive.  If this were the case, I
would not mix the kitten with a felv positive until she was a year and a
half and had been vaccinated (then I would consider it).  Kittens are the
ones that have the most difficulty  with this disease and die early.   To be
honest, if you believe the first test, now would be the time to try and
treat the cat as you may be able to clear the virus at this point - that is
a very debatable statement).  Kittens have an immature immune system and it
has been found that felv positive kittens have thymic hypoplasia (very small
thymus - thymus is responsible for making T-cells, a very important part of
the immune response in this virus).  It appears that the virus can actually
inhibit the activity of the thymus.  LTCI injections appear to attempt to
halt and reverse this process.
Hope this helps and good luck.  God bless.

Jenny

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