From:
poof242@aol.com
Date: 2001-06-29 08:30:00 UTC
Subject: Aleutian Disease Question
This is something that I copied from the FML, hope it answers some of your
questions:
Tue, 31 Oct 2000 09:18:13 -0500
From: avecon <avecon@E...>
To the FML:
I've been involved in a recent discussion concerning possible false positive
results by CIEP for ADV Antibody along with Drs. Williams and Bloom. It is
my contention that a false positive reading is possible for two reasons (I
respond here with some of the same language used prior in this discussion):
First, the basis of potential false positive results would not be
cross-reactivity with distemper virus, antibodies to distemper or any other
virus (including parvovirus) or their antibodies. The basis for this is the
production in ferrets of antibodies to cellular debris in vaccines, present
as a by-product of their manufacture in cell culture. Similar cellular
debris may be present in the whole ADV viral lysate (actually a mixture of
several ADV-related proteins, or antigens) used in the test. When antibodies
to this debris in the ferret serum encounter the ADV lysate in the test a
precipitate line can be formed which is similar to an ADV Antibody positive.
Especially in cases where the ferret is tested by this technique within 2-3
months of receiving a vaccine I believe there is some likelihood of a false
positive result due to this phenomenon. Even United Vaccines notes the
possibility of false positives from recently vaccinated ferrets.
Second, and admittedly subjective, is the issue of reading results. As I
understand it, the CIEP result is determined by an operator's judgement as to
whether a precipitate line is formed in the gel, which is a subjective method
itself. In my conversations with Dr. Bloom, he indicated that with any
questionable result in his laboratory, the CIEP gel is washed and further
treated with a protein dye stain for better visual detection, and the
interpretation thus confirmed.
I don't wish to contradict Dr. Williams, but I must respectfully add that Dr.
Bloom did not say outright there are no false positives associated with CIEP.
He points out that there conceivably are false positives, but there is no
peer-reviewed evidence to prove it or the contrary. As I mentioned, even
United states concerns about testing around the time of vaccinations. While I
have not seen data as to the accuracy, sensitivity or specificity of CIEP, I
agree that anyone who has a CIEP positive ferret should take appropriate
steps to isolate the ferret and not equivocate, because of the nature of the
danger involved.
As a disclaimer, let me say that my organization is one of the groups
mentioned by Dr. Williams as being involved in the development of a new
diagnostic tool for ADV Antibody. I do think that the ELISA we've developed
is a better diagnostic test for ADV Antibody for several reasons. When we are
finished with our clinical/other studies I will demonstrate this with the
data in the appropriate forum. I plan on being at the Pennsauken show on
December 2, and would be happy to discuss these issues with all present.
Sincerely,
Robert L. Stephon, Ph.D.
Avecon Diagnostics, Inc.
"Bruce Williams, DVM" <williams@E...>
There are certainly a number of ferrets that will test positive for the
disease (running the CIEP test, which measures antibodies to ADV in a
ferret's blood.) The presence of antibodies shows only that the animal has
been exposed to the disease and is mounting a response.
The problem with AD is that the disease itself is largely a result of the
OVERPRODUCTION of antibodies against the virus. These antibody-antigen
complexes precipitate out in the blood vessels around the body, causing
disease and ultimately death.
There is a percentage of animals that will be in contact with the virus,
mount an antibody response, and in doing so, clear themselves of disease.
But especially early on, it is impossible to tell whose response will be
appropriate and stop, and whose will go into overdrive and result in clinical
AD. This is why we always retest antibody-positive animals 6 months later
(and often again after that.)