From:
RRC
Date: 2001-07-03 11:33:00 UTC
Subject: Bob C: ADV and Ferrets, or, Epizootic VI: The Return of the
Nadir
Christopher wrote:
>Bob Church's...prediction that ADV would pretty much sweep
>unchecked through the ferret community in a pattern similar
>to ECE.
I have made this statement several times, and I remain convinced it will
happen sooner or later IF established public health procedures which
prevent the spread of disease are not followed. It almost cannot not
happen if current practices by shelters and ferret shows are not changed
to contain this very real problem. The REAL danger is that ADV could
potentially skip the Atlantic and do it's nasty deeds in Europe. And
over there, not just domesticated ferrets are at risk, but so are
European and steppe polecats and the European mink. While none of these
species are currently endangered with extinction, there are local
populations at risk. My expertise comes from a intensive
zooarchaeological study of infectious disease to explain Post-Columbian
wildlife declines and to refute the Pleistocene Overkill hypothesis.
That does not make me an expert on ADV, and I encourage those with a
better understanding to improve on or correct these efforts.
I am not going to waste people's time by trying to do a review of ADV;
there have already been several webpages mentioned which do a good job
and the disease has been discussed in great detail here. What I will
discuss is HISTORY, so my remarks can be understood in the context in
which they were meant.
In 1492, Columbus sailed the ocean blue. You might remember that little
rhyme from grade school. What the rhyme never revealed was introduced
European diseases, including smallpox (poxvirus complex), measles
(canine distemper/measles/rinderpest complex), cholera, bubonic plague
and other diseases, sailed the ocean blue with him. There is no agreed
upon population numbers for Pre-Columbian Native Americans, but it is
generally accepted that whatever those numbers were (somewhere between 5
and 9 million), between 70-90% of them died from introduced diseases
within a century of Columbus's first visit. Some areas of the Caribbean
and southern Florida were virtually denuded of humans. The loss of human
life was so great that it destroyed the oral history of most tribes, and
the survivors couldn't explain who built the vast monuments and mounds
in the Midwest and East. The death toll reached millions in what one
scholar called "Native American bacteriocide". I have read journal
accounts of people finding villages long abandoned by everything except
the skeletons. Not just one wave of disease ravaged the Native
Americans, but wave after wave every generation or so helped European
expansion during the days of the Monroe Doctrine. When Lewis and Clark
visited Mandan villages in the early 1800s, the people had just
recovered from a smallpox epidemic which reduced the number of villages
from about a dozen to just a few (the Northern Plains Native Americans
suffered an epidemic every 5.7 years on average from 1682-1920). The
southern Washington archaeological site I am involved with was abandoned
prior to 1830s when local populations dropped from the thousands Lewis
and Clark saw to hundreds because of a combination of introduced diseases.
There is a term for this type of spread of disease; it is called a
"virgin ground epidemic." In other words, it is a disease which has
never been seen before by a population, and it spreads like wildfire,
usually with devastating results. Bubonic plague was a virgin ground
epidemic in western Europe, and killed millions of people in a single
generation. It did a similar thing on a smaller scale in Central and
South America during the time of Spanish conquest. Currently, AIDS is a
virgin ground disease in humans. The same thing happens in animal
species; in the 1920s foot and mouth disease spread into the California
mule deer population, killing more than 20,000 deer. It is very probable
the initial decline of the black-footed ferret was due to the
introduction of canine distemper (I just returned a reviewed paper on
this subject for second review). When plague was introduced into the USA
in 1907, it spread through the rodent populations like wildfire, and can
now be found throughout the west in ground squirrels, prairie dogs,
marmots, and wood rats. Canine distemper is currently spreading through
Africa, killing jackals and African wild dogs, and has been reported
(but I am not sure if confirmed) in African lions and hyenas. Rinderpest
is likewise infecting antelope and wild bovines. Wildlife epidemics
(epizootics) are quite common in recorded history, and were probably
responsible for the decline of the Pleistocene megafauna, helped perhaps
by Paleoindian over hunting and climate change. In fact, according
Swabe, the rise of veterinary medicine was a response to increasing
epizootics resulting from trade, conflict and population growth during
the 1700s.
Virgin ground diseases seem to fester, sporadically infecting what
appears to be isolated populations, then snowball exponentially into
major epidemics. Because they have never seen the disease before, the
victims have little resistance to infection. In many cases, if the
disease is a virus, it is recent species crossover; that is, a variant
of an existing disease infecting another species (the canine distemper
variant in humans is measles; in cattle it is rinderpest). Recent
species crossovers TEND to be moderately virulent (not always), and
initially have high morbidity (ratio of infected to healthy individuals,
sometimes called the infection rate) and mortality (death rate). This
usually changes as those individuals with the more virulent forms die
and fall to pass on the nastier variants of the disease, as well as
individuals developing immune responses and passing them to offspring.
If the incubation period of the disease is short and the disease has a
limited period of expression, it can burn itself out by killing the
local population and leaving no hosts alive. However, if the disease has
a long or hidden incubation, and rarely kills individuals prior to
sexual maturity and reproduction (like AIDS and ADV), it has a very good
chance of establishing itself so solidly within a population that it
will never be totally eradicated.
ADV is acting like a classic virgin ground disease in domesticated
ferrets. It is a recent species crossover (about 50 years old). It is
not all that virulent (compared to influenza, ECE, or canine distemper).
However, even with a relatively low virulence, in areas where it has
gained a foothold (mostly shelters), it seems to have a moderately high
morbidity, and we are all aware of the mortality rate hovering at the
100% mark. I think we have been watching the slow growth for some time
now; as more and more ferrets are tested, I fear we will begin to see
the beginnings of exponential growth that is already seen in AIDS. The
problem with a disease which has a long incubation period and a long
period of infection is that you could already be in the period of
exponential growth and not know it.
Just because ADV is acting like a virgin ground epizootic, it doesn't
necessarily follow that it has to BECOME one. We can look at history,
recognize the signs, and use established public health procedures (and a
good deal of common sense) to prevent ADV from entering the exponential
portion of the growth curve. We could try:
1. Testing all ferrets for ADV prior to breeding, sale, adoption,
introduction to other ferrets, or geographic relocation.
2. Isolating all infected ferrets. As drastic as it sounds, in some
instances, culling may be the best public health solution. I do not
advocate euthanasia lightly, but the dead truth is, it is better to lose
a few than to lose a lot, and while the option may be rightly
discouraged (especially with private ownership), it should never be eliminated.
3. Requiring certificates of testing for entering shows or ferret
events, as well as requiring judges take precautions.
4. Creating a central data bank to monitor outbreaks of ADV, recording
type of ownership (private, shelter, etc.), date of diagnosis, breed,
geographic location, age, sex, etc., and which follows up to record
death information. This could perhaps be the project of a ferret club or
an individual with a web page and little else to do.
5. Establishing an accepted method of disinfect ion which is effective,
uses commonly available products, and is easily carried out by people of
limited means and abilities. This has got to be simple and effective;
just remember how many cases of AIDS that might have been prevented if
someone had used a condom. Hard to find something simpler than that.
6. Convincing breeders and pet shops to make information regarding ADV
part of the package given to new ferret owners.
7. Contributing to ADV research.
Will these ideas work? Probably not totally; there will always be the
odd ferret owner who doesn't care and takes no precautions. However,
since there is currently no cure for ADV and no hope for recovery, the
best solution is prevention. History gives us a good idea of the
potential for ADV to become a modern ferret plague, but we don't have to
repeat past mistakes. We can learn from history, take the appropriate
public health steps, and enjoy our ferrets for a very long time.
Bob C