From:
Danee
Date: 2005-06-10 22:06:36 UTC
Subject: ADV Update - Part 4
To: "Ferret Health List" <ferrethealth@smartgroups.com>
Message-ID: <42AA0EEC.2080403@aol.com>
Permission to cross post the following information to other lists is
granted, as long as the post is taken in it entirety, with out any
changes or additions.
When the research team at UGA started out, they determined that the
tests that were currently available were not accurate enough and not
specific enough for their purposes. They needed to do more than verify
the presence of ADV. They needed tests that would qualitatively and
quantitatively describe going on with the virus and the animal=E2=80=99s bo=
dy.
And so, starting with the Counterimmuneoelectrophoresis (usually called
CEP or CIEP) test, and working from there, they have worked with and
developed several tests that will meet their needs. With the CEP test,
they started reporting results using titers, rather than just reporting
a positive or negative result. Titers give an idea of the concentration
of the antibodies in the animal=E2=80=99s blood stream.
Titers are accomplished by a series of dilutions of the test sample with
a non reactive substance, and testing until a negative result is
received. For example, they would start with one part of the blood
serum, and dilute it with 4 parts of saline, and test. If the result
was positive, they would then use a dilution of 16, then 64, 256, 1024,
etc. The amount of the dilution would increase in powers of 4. The
higher the dilution needed to achieve a negative result, the greater the
concentration of antibodies in the test sample.
With studies that were previously done on mink, there was a correlation
between the titer level and the health of the animal. Once the titer
reached a certain level, the mink usually died within a few weeks. In
both mink and ferrets, they consider dilutions of 4 and 16 to be low
titers, 64 and 256 to be moderate titers, and 1024 and above are
considered a high titer.
What they found was that with ferrets the titer level was not a good way
to judge the likelihood that the animal was nearing death from ADV.
Many ferrets with high antibody titers went on to live several years
with the titer remaining constant.
Even though using titers with the CEP gives additional information that
was not offered with commercial tests, it was still not enough. The CEP
test is an antibody test. It verifies that the body has been exposed to
the virus, and has created antibodies, but it does not prove that the
virus is still there. So, a test for the actual virus, or antigen, was
needed.
One of the first tests they worked with after the CEP was the PCR, or
polymerase chain reaction. The PCR test can be used to detect any kind
of viral DNA in a sample, and yields a simple positive or negative
result. The PCR is not used only for ADV, and in fact, there are now
PCR tests for AIDS that are commercially available.
The PCR test for ADV is usually run on a fluid sample. Initially, all
of the blood samples they received from us from ferrets that had tested
positive with United=E2=80=99s CEP test tested positive for antibodies, but=
were
negative for antigen. This did not mean that the ferrets that were
providing samples did not have the virus, just that it was not present
in their fluids.
With ADV, often the virus settles in the organs. When this happens, the
ferret is not in a contagious state, because unless his organs are eaten
by another animal, there is no way for the virus to move to another animal.=
But sometimes, in some ferrets, the virus moves into the bodily fluids,
and can then be transmitted through the fluids to other ferrets. When a
ferret=E2=80=99s blood, saliva, feces or urine tests positive with a PCR te=
st,
then that ferret can transmit ADV to other animals.
The PCR test could be very useful to ferret owners if it could be run in
their vet=E2=80=99s office, because it would let them know if a ferret that=
was
ADV+ was contagious at that moment in time. Unfortunately, it is
unlikely this will happen in the near future. To run it requires very
expensive equipment, and a highly trained technician who is familiar
with the procedure. Some of the commercial labs may decide to offer the
test, but since there would be a lag time in getting the results, it may
lose some of its meaning. The test would only tell you what was
occurring at the time the sample was taken, and while it is unlikely the
status changes rapidly (like overnight), it is possible. So, the PCR
test is something that is more useful from just the research standpoint.
It is important to remember that a negative PCR test does not mean a
ferret does not have ADV, just that the virus is not present in the
fluids at that time. A positive result is a conclusive proof that the
ferret has ADV, though
One test that the U of GA developed, and has made commercially available
is the DNA in situ hybridization test. This is a test run on tissue
samples taken either during necropsy or biopsy of organs, and is
extremely accurate. Again, this test can be set up to find a number of
different viruses. But, UGA has modified it to use in identifying ADV
viral particles.
This test is very valuable to the research team, because it highlights
where the virus is in the tissue samples, making it easier for them to
study. From a diagnostic standpoint (or from the ferret owner=E2=80=99s po=
int
of view), it is an extremely accurate test that will let them know for
certain whether or not a ferret has ADV. However, because it requires a
tissue sample, it is not a good starting point for testing.
Finally, the UGA team has been perfecting an ELISA test for ADV. ELISA
is an abbreviation for "enzyme-linked immunosorbent assay=E2=80=9D. ELISA =
tests
are widely utilized to detect substances that have antigenic properties,
primarily proteins (as opposed to small molecules and ions such as
glucose and potassium). The substances detected by ELISA tests include
hormones, bacterial antigens and antibodies.
The ELISA test that UGA has developed for ADV will give a result
expressed in titers (actual numbers, not just low or high). It will not
be the same as the ELISA test offered by Avecon Diagnostics. The Avecon
ELISA is an antibody test. I do not know enough about the UGA ELISA to
say whether it will test for antibodies or antigen. While they have
developed this test primarily for use in their research, they may be
making this test commercially available in the near future, as they feel
it will provide veterinary professionals with another highly accurate
test to detect ADV.
Developing these tests and insuring their accuracy was an important
first step in the process, and was necessary before any other steps were
taken. During this time, the team was accepting samples from ferrets
from members of the ferret community. This was beneficial to both
parties. The team had samples without having to infect more ferrets
with ADV, and the owners who provided the samples got free testing.
Now that the test development stage is over, the tests that are useful
to vets and owners will be offered commercially. This also benefits the
program, because it brings in money to cover expenses, freeing up the
money that gets donated to cover the next phase of the research. I am
certain that many people who donate do not want to think their funds are
being used just to provide free testing to some individuals.
But, the ferret owners who did provide samples during these early years
should all be thanked. I only know a few of the names, and know there
are many more who I don=E2=80=99t know by name, so I will not try to pinpoi=
nt
who these owners are. But, without their willingness to help, some
ferrets would have had to be deliberately infected with ADV.
Fortunately, to date, that has not had to happen.
When I post again, I will talk some more about where the research
currently stands. I may take a break for a day or two, though.
-- =
Danee
International Ferret Congress Health Issues Coordinator
http://ferretcongress.org
ADV - If your ferret hasn't been tested, you don't know!
For more information visit: http://www.ferretadv.com
You can help fight ADV! Visit:
http://help4adv.terrabox.com/