I was reading a book today entitled "Rabies" by Virginia Alvin & Robert
Slverstein.  It describes a number of diagnostic tests which can be used to
test for rabies.  Of particular interest to me were the ones used in humans,
because naturally they are trying to do the diagnosis before death, and we
would like to be able to do a nondestructive test on ferrets if they are
involved in a bite incident.  (Good book, clear & well written, LOTS of
references for those of you looking for literature to back up quarantine
fights.)
 
This book is pretty recent (1993), and the bottom line is, there isn't a
good reliable nondestructive test for humans either.  All can yield
unacceptable rates of false negatives.  The methods that were described:
 
1)taking a glass slide and pressing it against the eye to collect corneal
cells for staining with the flourescent antibody test.  Apparently the
cornea gets infected about the same time as the salivary glands.
 
2) Spinal tap, which was described in the 6/10 FML
 Anon poster FM wrote:
>The test involves analyzing a sample of spinal fluid for the virus and
>actually has a lower incidence of false results.
 
FM, I think you misunderstand the test.  It was described in the book as
testing for antibodies to the rabies virus,(not the virus itself) because
they are developed by the body while trying to fight the disease.  The
problem with the test is that in a rabid animal/human the antibodies don't
develop (in humans) until day 8-10 of the disease.  The case of a CA 11 year
old in 1992 who began displaying classic symptoms of rabies was described.
The spinal tap came back negative, as did an initial skin test (see below).
They began treating him for rabies anyway.  Another skin test 4 days later
came back positive.  He died.  He had apparently contracted the disease two
years earlier in India from a dog and been incubating it.
 
That being the case, I think the health dept was right to reject a spinal
tap (assuming they actually knew what you were trying to describe); not only
is it unreliable in a suspect animal because it would show a positive late
in the disease, but I'm assuming Kodo would have been expected to show
positive to the test, because since he was vaccinated, he should have had
antibodies.
 
3) Skin biopsy taken from the nape of the neck is subjected to the
flourescent antibody test.
 
The possibility of checking a blood titre to see if sufficient antibody
levels were present to determine if vaccination was successful wasn't
described at all in the book.  I don't have any info on that possibility.
 
It's my understanding (but third hand info, not direct from health dept)
that it's not considered acceptable because there aren't standards (for
nonhumans) as to how high is high enough.  I don't understand that
perspective, since I'm assuming that's how they check to see if the darn
vaccine is working in clinical trials, and something along that line is
probably used to get the USDA approval.
 
So I believe we're left with quarantine.  I can understand the concern that
ferrets might have a longer shed period than would be acceptable.  I don't
*agree* with the concern; certainly all existing studies support a
quarantine.  And since dogs have been known to shed more than the acceptable
10 day quarantine (the same book mentioned that dogs have been known to shed
the virus while appearing healthy for two YEARS.)  So the quarantine doesn't
guarantee safety with dogs.  If some small risk is acceptable with dogs and
other animals, it should be for ferrets too.
 
One last comment.  Someone mentioned a few days ago that concern over the
carp rabies variant might surface, after testing is finished for the
platypus strain, (which I believe is tentatively scheduled for June 2023)
 
I don't think that there will be concern over that because rabies only
occurs in mammals.  Of course, viruses do mutate, but heck, what's the
possibility that it would mutate into something a fish could catch?  Why,
that's about as big a risk as, say, a vaccinated ferret that appears healthy
for over a month shedding the virus on the first day of his confinement.
("Officer, sieze that goldfish!!!")
 
-Ilena Ayala
[Posted in FML issue 1971]