Several people have written to me saying that ferrets are in fact
sensitive to pyrethrin insecticides. I have looked into this quite a
bit and I would like to try to clarify matters somewhat. Among other
things, I probably did not emphasize certain cautions as much as I
should have. But let me say up front that this is all about informed
choice. We need to look at the facts and evidence on both sides. So
pardon the length of this email, but I want to present as much as I
can. I had to split it into two different emails due to length, but
I think it is warranted. I guess I should also preface this with the
statement that I am not a vet. But I have tried to do my research,
including looking things up in veterinary manuals that I could find.

First, I should say: ferrets have proven to be more sensitive to
insecticides than most mammals. Something may be safe for dogs or
even cats, but not ferrets. So whatever medication you use, use it
with caution.

Second, I must apologize for even mentioning permethrin. It is a
synthetic pyrethroid that appears to be safer for many mammals than
pyrethrin itself, but some animals have shown a higher toxicity to it
than pyrethrin. Permethrin is apparently okay for dogs, but should
never be used on cats or ferrets.

I have had a couple of people tell me that they or a friend lost a
ferret due to pyrethrin flea treatment. However, without knowing more
about the particular situation, it is likely that the toxic factor was
an additive, not pyrethrin itself. In particular piperonyl butoxide,
but other additives may be harmful as well. I did warn about additives,
but probably not strongly enough.

The vast majority of evidence says that pyrethrin -- pyrethrin alone,
not permethrin or pyrethrin with other additives -- is generally safe
for ferrets if used as directed.

One article that somebody referenced ("Literature search for
mustelid-specific toxicants" by M.L. Wickstrom1 and C.T. Eason) states
that ferrets are "sensitive" to pyrethrins "at high doses"... but that
paper was about how to poison ferrets in New Zealand, where they have
a ferret population problem, and so it is approaches the issue from
the opposite angle than what we usually see. In general, the paper
discussed doses much higher than those seen in normal use.

Just so there is no misunderstanding, here is a quote from the paper.
It seems pretty alarming at first.

More than 50% of the fatal mustelid exposures identified in the
clinical veterinary toxicology databases involved pyrethrin or
pyrethroid insecticides applied dermally to pet ferrets or to the
animals ' environment, for controlling fleas or other insect pests.
Although doses could not be determined, in most cases the use of the
agent was appropriate, indicating that ferrets may be highly sensitive
to this class of insecticides. Clinical signs included diarrhoea,
weakness, neurological signs ranging from ataxia and mild tremors to
seizures, renal failure, and death.

Note, however, these facts:

(1) They say the "use... was appropriate", while at the same time
saying that the dose was unknown. This is a self-contradiction. Without
knowing the doses involved, it is impossible to tell whether the use
was "appropriate".

(2) They say "More than 50%" of the cases were from pyrethrin or
pyrethroids, but their own chart on the following page shows only about
21%. Additionally, insecticides already known to be much more toxic
have fewer case numbers in their chart; this may be because of the
easy availability of commercial pyrethroid flea preparations. In other
words: it is as likely as not that the higher number of reported
incidents is merely because it is used so often, by so many people.

(3) Note the use of "pyrethroids". This would include permethrin and
other more toxic compounds, as well as the additives I mentioned
earlier. In this paper, no distinction is made between pyrethrin and
other similar chemicals. They are all lumped together.

(4) The context of the entire paper must be kept in mind. Their use of
"highly sensitive" is in the context of poisoning ferrets with high
doses of chemicals.

(5) The actual number of reported problems with ferrets cannot be
determined by the information in the paper. They cite 9 "cases", with
each "case" representing anywhere from 1 to 22,000. So the number of
actual reported incidents could be anywhere from 9 to 198,000 animals.

(6) Acetominiphen (tylenol) is shown in the same chart with 7 reported
"cases", which is about 17%, or 7 to 154,000 animals. Acetominophen
is known to be toxic to ferrets, but unlike a flea spray it is not
something that most people give to their ferret intentionally. So I
think that says something.

Need I point out that ranges of numbers this huge are vague leave big
questions about any statistics that appear in this report? Maybe the
number of ferrets that succumbed to "pyrethroid" poisoning was only 9,
while the number that died of acetominophen poisoning was 154,000. Or
maybe it was 198,000 and 7, respectively. We just have no way to know.

In short, when it comes to home use of pyrethrin, this paper actually
says very little that is of any real use. Which should be no great
surprise, since that was not the subject of the paper in the first
place.

In searching the literature (I have read a lot just since yesterday), I
found a few references to people who claimed their ferret became ill or
died after exposure to pyrethrin. But again, they do not say: was it
actually just pyrethrin, or a known-to-be-more-toxic pyrethroid? Were
there harmful additives?

Here is an important fact: pyrethrin-based insecticides have been used
on thousands of ferrets, hundreds of thousands or even millions of
times total, at home and commercially, for many years. Some ferrets
may be extremely sensitive to it, but if so they are relatively rare,
otherwise the millions of uses would have resulted in many more horror
stories than we actually hear about. Pyrethrin is recommended for use
on ferrets by many veterinarians, and also by the Merck Manual of
Veterinary Medicine.

Humans in general are notoriously bad at risk assessment, and tend to
raise alarm over very small statistical risks. For example: if you are
a frequent flyer, are you more likely to be (A) injured or killed in an
airplane accident OR terrorist attack, or (B) injured or killed by a
fall in your bathtub?

If you answered B, you would be correct. By a long way. Yet we don't
have people in uniforms standing around our bathtubs to ensure our
safety. Why? Because falls in bathtubs are a statistically rare
occurrence, and we know this. But when they do happen, they don't
make the news. They are not considered newsworthy (or perhaps are
too embarrassing). But a plane crash is reported all over the planet
within hours.

We allow intrusion and abuse by the TSA in airports because of a
misplaced perception of the risk, which is actually ridiculously small.

The same is often true of our pets. Take the recent issue of the ferret
and the baby for example. With a few notable exceptions, the media have
ignored the fact that the ferret and the baby were left alone (the
parents were literally out of the house) for an unspecified period of
time. They also did not ask whether parents who would leave their baby
alone in the house might not also be likely to abuse pets... maybe not
feeding them adequately? I think it is pretty clear that the parents
were guilty of negligence at least, and that their situation does not
represent the vast majority of cases where ferrets are around babies.
Yet how many people are now afraid of ferrets because of it?

Similarly, I believe that the relatively rare (but apparently real...
I am not denying them) reported cases of ferrets who become ill or die
from pyrethrins are stories told over and over, but we never hear from
the thousands of people who use it frequently with no problems. Just
as peanuts are eaten by millions of people every day, yet they can be
lethal to some people with allergies.

[Posted in FML 7194]