[E3a]
Has there been a shift in the relative numbers of specific ferret
diseases, and if so, how have they changed?  By many accounts, this
question is one that cannot be answered.  However, such questions are
common enough in historic archaeology, where techniques have been
developed to address them.  One of those techniques involves the careful
scrutiny of historic documents, including older books detailing ferret
care, pamphlets, newspapers, and other such material.  Believe it or not,
there is a surprisingly large amount of such information regarding ferret
diseases.
 
Early accounts of ferrets generally ignore their health aspects,
concentrating on hunting and physical characteristics.  This gradually
changed with shifts in human attitudes towards animals, as well as the
rise of veterinary medicine.  Between the 1600s and 1800s, while
reference is made regarding the health of ferrets, with a few exceptions
nothing specific is mentioned.  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.
 
One of the first accounts to dedicate significant space to a discussion
of ferret illnesses dates to the late 1870s (there are others, but it was
the first to have a separate chapter on the health and care of ferrets,
not just a short addendum or mention).  In that account, the paramount
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
years.  There were a few farming publications that periodically discussed
ferret health issues; one had a weekly "ask-the-vet" column that,
over the years, discussed most of the then-current health problems in
ferrets.
 
Of all the modern diseases, two have significance for this discussion:
adrenal disease and insulinoma.  They are important because they have
unique symptoms.  Historic descriptions of those symptoms would be easily
recognizable (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.  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.  Vets a century
ago may have had simplistic skills compared to modern vets, BUT, they
were careful observers with great skills in describing unknown diseases.
If adrenal disease were common, it would have been described.  Even in
the ferret books of the later half of the 20th Century, when vets were
trained with more sophistication, the two diseases are mostly ignored
until the mid-to-late 1980s.  It is hard to ignore the visual
characteristics of an adrenal ferret, yet NONE are mentioned
historically.
 
Bob C
 
[E3b]
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.  This is a significant era because the first
book published solely recommending ferrets as pets was published in 1977.
Here is the really cool part.  When you graph the individual number of
ferret-as-pet publications and compare it to the number of reports of
ferret insulinoma and adrenal disease, you find the two highly
correlated.
 
We all know that, but the finding is more complex than a simple
correlation.  If the increase were only due to a simple increase in
numbers, then while the numbers would increase, they would remain
proportionate to the population as a whole.  For example, suppose adrenal
disease impacted 0.5% of the older ferret population, numbering 1000.
That means even if you increase the population to 2000, the relative
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.  But what I have found is for the last twenty
years, the RELATIVE rate of both insulinoma and adrenal disease has
INCREASED within the population.
 
This is very significant.  In population genetics, disease frequencies
are very stable in large populations like those existing in American
ferrets; shifting those frequencies is extremely difficult.  EVEN IF a
bottleneck occurred introducing both diseases into the American ferret
population, the resulting disease frequencies would stabilize at some
specific frequency, and while the numbers would increase or decrease
with population changes, the ratio would remain constant.
 
Both insulinoma and adrenal disease frequency rates have increased
from the 1980s to the late 1990s.  Ferret population has also increased,
but the relative frequency of one to the other- -the ratio of sick
to healthy- -has dramatically increased as well.  THAT suggests that
the mechanism spurring the increase is NOT the result of a genetic
bottleneck.  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.
 
One of the basic principles of population genetics is that genetic
disease frequencies are remarkably stable.  Change means adrenal disease
and insulinoma are not only increasing in USA populations, BUT that the
increase is not due to simple genetics, but something else.  If the
problem was caused by a founder's effect, then relative frequencies of
disease would stablize, but they are increasing, and not just in the USA.
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.  In most of
these countries, the difference isn't in housing, lighting conditions,
neutering, or even genetic bottlenecks.  It is diet.  The late onset of
adrenal disease and insulinoma mirrors the increase in use of an ad
libitum, kibbled diet.
 
Bob C
[Posted in FML issue 3967]