I found the historical info very interesting and well written. I had
more reservations about the genetic section due mostly to it completely
overlooking the marked change in proportion of fancies within the
population.
>Of the mentioned diseases, canine distemper ranks high (usually implied:
>it is frequently recommended to keep ferrets away from dogs), followed
>by foot rot and scours commonly caused by spoiled milk.
Interesting. It makes me even more grateful that there are now vaccine
for CDV, and that Merial has developed a type of CDV vaccine with which
the using vets have several times mentioned reduced reaction rates. Of
course, part of that feeling is because we heard of way too many ferrets
lost to CDV this year.
>One of the first accounts to dedicate significant space to a discussion
>of ferret illnesses dates to the late 1870s ... diseases mentioned are
>canine distemper (sometimes called the sweats), a vague disease also
>called the sweats that is probably a form of influenza or other
>upper-respiratory disease, scours, foot rot, and complications from
>mange, flea and rat bites. In that account, ferrets lived to 5 or 6
>years of age. These health problems, with minor deletions or additions,
>are mentioned repeatedly in ferret-related documents until the mid-1900s.
>During this time, ferret lifespan is reported to range from 5 to 9 years,
>with an average age at death about 5 to 6 years, and a maximum age of 12
Okay, so in most cases the ferrets were passing away at ages lower than
the most common ages for adrenal neoplasia or insulinoma, or around the
ages when they usually begin to be most commonly seen. (This is because
you report the average age of death as being 5 to 6, so the older ones
were very rare to have had almost no effect on the average figure.)
>Historic descriptions of those symptoms would be easily recognizable
Agreed for the most part, though I sure know that balding was
misinterpreted earlier due to one of our's. This is why I tend to
think that impression that they may have been more rare here in the U.S.
during the "Days of Meow Mix and Raisins" 15 to 20 years may be valid.
>(new ferret owners easily describe the symptoms of both diseases, and
>the descriptions are easily recognized by long-time ferret owners), and
>while they generally impact older ferrets, they occur in younger animals
>as well.
I tend to find the young occurrences interesting and puzzling. We've
personally only that that happen ONCE in twenty years -- one ferret with
two bad adrenals at age 3 or 3 and 1/2. We thought we might have a
second one with an adult adoptee but the vet said that we estimate ages
too low and she was a decent chunk older. I know that some folks have
told me that they are more likely to see the very early ones with ferrets
who have noticeable KIT or WS genetics, but I do not know if that is an
abberation of the reporting and sampling mode which it could be.
Otherwise, the adrenal cases and all of the insulinoma cases here have
been over age 5, most of those being over ages 6 or 7 years, especially
for insulinoma in our household population. (Of course, that is
anecdotal so i have no way to know if we have been merely lucky or are
doing something right, or partly right, in that regard.)
>In short, they are diseases that, if present, would have been recognized
>and described. Arguments that early vets lacked the ability to recognize
>them are, well, obtuse.
Yes, and no. When we had our first ferret with adrenal neoplasia his
problem went undiagnosed for a while -- despite having sequential exotics
vets -- until he went to someone who had recently left the AMC and was
familiar with (then) new work showing that the balding was not age
related. Since the adrenal situation wasn't known and since people so
often tend to think of baldness and age together we actually wound up
going to her (Liz Hillyer) because of his related skin problems. (BTW,
just an aside: both our first pancreatic and our first adrenal problems
here were related to cases of lymphoma in a lympho clump.)
>It is hard to ignore the visual characteristics of an adrenal ferret,
>yet NONE are mentioned historically.
Even today, though, we do hear at times from folks who think of age
in relation to baldness. Not saying that definitely played into the
reporting, just that it could have done so. Seizures would be a lot
harder to miss, though some ferrets do have insulinoma progress slowly
and have it not found until it is advanced and such individuals could
die before a person catches on -- but that isn't the norm.
I think that the fact that so many of these ferrets died before or around
the time when such diseases are most commonly presenting themselves may
say that it is possible (Note the qualifier.) that many died before they
had a chance to develop them. I don't personally think that is what
happened, but it is a possibility, and like everyone else I've had
suspicions turn out wrong in the past, so a large factor like this can't
be eliminated from the possibilities.
>I have scoured more than 1000 historic documents to graph the relative
>frequency of ferret illnesses, finding some 380+ mentioning ferret
>disease. In these documents, both insulinoma and adrenal disease are
>RARE until the mid-1980s.
That is about when the first research into treating these things began
happening.
>number of diseased individuals would remain constant at 0.5%. You would
>see an increase in ill individuals, but they would remain proportionate
>to the population as a whole. This is what you see in with a genetic
>ailment, which is why scientists can cite specific rates of disease for
>specific populations.
I don't think that you expressed this clearly. What is seen when there
is a genetic component is a rate change that reflects NOT the population
numbers but the presence in that population of the allele or alleles
which increases susceptibility to a disorder, and that expression tracks
in multiple ways, depending on if the allele(s) are needed:
1. in combination (if multiple alleles), 2. in a double dose (if one
allele), 3. as one representative of that allele, etc. (An allele is
a variation of the gene for a given location (locus) in the genetic
sequence for those who don't know.) Anyway, if the proportion of
individuals in the population who have the allele(s) in question remains
the same then the level remains constant, but if the proportion increases
(as with a demand to breed more fancies) then the rate of the related
illness(es) seen increases. Demand for fancies markedly shifted the
appearance of ferrets in very few years -- a rapid change in genetic
components. Does this play into the problems under discussion? I don't
know, but it may. 20 years ago it was almost impossible to see ferrets
who were not standards or albinos, and most of those were standards.
When a few fancies were seen absolutely huge prices were demanded and
gotten: about 8 times what normal ferrets were being sold for around
here. The fancies got into demand and wham(!), the fur stock ferrets
which had not been bred for longevity but had been bred for fancy fur
showed up locally in bred into one of the farm's populations and in a
few years there were some in every lot being sold. Now, in ferret lots
around here half or more will commonly be fancies. That is a HUGE
human-created genetic shift.
>This is very significant. In population genetics, disease frequencies
>are very stable in large populations
Unless the changes are purposely bred for as happened with fancies; then
such changes can be rapid, as this change was. It is easy to rapidly
change proportion of alleles with selective breeding. If it weren't so
then almost all of the ferrets out there would still be the standards --
self patterns with black or brown fur -- or albinos same as they used to
be, with fancies only extremely rare, but we KNOW the proportion of
those alleles increased because now there are a lot of fancies: reds,
butterscotches, DEW, patterned whites, blazes, pandas, mitts, spotted,
grays, etc.
>THAT suggests that the mechanism spurring the increase is NOT the result
>of a genetic bottleneck.
If what you are saying is that it reduces the chance of this being the
result of possible low genetic diversity in the U.S. populations, that
i agree with, but it could still be related -- in full or in part --
to changes in the presence of some alleles preferentially bred for in
fancies due to their marked change in their proportional representation
in the population through selective breeding.
>While adrenal disease and insulinoma are certainly the products of gene
>expression, it is not simple genetics driving the increase in relative
>frequencies of either disease.
I also think that you are right in that. My personal suspicion is that
some fancies (such as the KIT or WS ones) may get some of these common
diseases at YOUNGER ages -- that this may be where the age decrease in
expression might be coming into the picture, at least in part. That is
only a suspicion, and is based on reports of very few blazes and pandas
living as normal lifespans and what folks have said that they got early.
(In other words, there is not a scientific sampling on this, but it has
some interesting hints of things possibly worth investigation in case
the age of onset may be genetically influenced, or if those genes may
interplay with things like too little true darkness and early neutering.)
>In the last few years, adrenal disease and insulinoma rates have been
>reported on the increase in other countries, including Britain, Denmark,
>the Netherlands, German, Australia, New Zealand, and France.
True, and one of the Australian area adrenal distribution reports looked
like it might follow a viral distribution pattern but then it wasn't
followed up on which was a real shame.
[Posted in FML issue 3968]
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