[Best Viewed in Netscape]
-
From: Dr. Bruce Williams
williamsb@AFIP.OSD.MIL
Date: Oct. 30, 2000
ADV test - false positives
Recently there has been a lot of talk about the veracity of
the CIEP test available through United Vaccines, about whether
there is a high incidence of false positives - animals that
will give a positive test for reasons other than possessing
antibodies to the ADV virus. Most of the discussion centers
around animals who have been vaccinated against other diseases.
Let me first say that I do not consider myself the last word
on this test, but Dr. Marshall Bloom, who may be the most
widely published scientist in the area of ADV (and who helped
to design the CIEP test), IS.
The main question regarding the test is that whether animals
who have been prviously vaccinated against canine distemper or
canine parvovirus (a common ingredient in dog distemper
vaccines) or other subcomponents of that vaccine would test
positively for ADV antibodies. Dr. Bloom does not believe that
this is a problem, and has never seen this phenomenon. Indeed,
all of his experimental animals (mink) are vaccinated against
mink enteritis (another parvovirus) and canine distemper, and
they don't cross react on the CIEP test.
I think a lot of this "false positive" assumption comes from a
number of sources - positive reactors that have ADV but die
early of other causes, so are termed "not having the disease",
other parties developing competing tests (there are several
groups who are in development right now), and a natural desire
for hope, however small. Several years ago, people were
posting on the Internet about being able to cure distemper by
injecting serum from vaccinated animals into affected animals
- 1 cc intraperitoneally. I am all for hope, but not when it
puts others at risk.
Marshall Bloom is still the expert on this question, and he
does not believe that false positives, if the test is run
correctly, exist. Until someone can back that up with some
real data, I've got to go with his experience. (However, I'd
love to see any data to the contrary - if United Vaccines or
any other group is saying that there are false positives, I'm
hoping they'll share some data with us...)
What actually concerns me more at this point is the possibility
of false negatives. Even in the hands of an expert, this test
may have 3% false negatives (that's published and in mink) -
animals that do not react for some reason or another. But
that's another story, and one that has yet to be worked out.
Last weekend Colleen and I adopted two ferrets - you can bet
I'll be testing for Aleutian Disease this time around.
With kindest regards,
Bruce Williams, DVM, DACVP
From: Robert L. Stephon, Ph.D.
avecon@EMAIL.MSN.COM
Date: Oct. 31, 2000
Response [ADV testing]
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.
Aleutian Disease Virus...in FERRETS |
White Russian's Mom's ADV Web-Site Pages
Other ADV Web-Site Pages
- Aleutian Disease |
A Hidden Danger to Your Ferret |
And for some history and a look further:
 | This Ferret Family WebRing site is owned by Wolfy's Wondifferous World of Weasels...Ferrets, that is!!!!. |
 |
| [ Previous | Skip Next | Random Site | List Next 5 | List All ] | ||
|---|---|---|
