Pet Forum / Mammals / Rats / August 2005

REPOST re: BUMBLEFOOT

Bumblefoot & soar hocks are lay terms for pododermatitis. Many people are
under the mistaken impression that "wire cages" CAUSE bumblefoot -- it's a
myth that is repeated & repeated & never apt to be weeded out of the
amateur community, though the belief causes the contagious infection to be
spread because the mistaken "treatment" is to remove all the rats from
contact with wire rather than to separate infected animals before others
are infected, & sterilize all surfaces for staph. My main source for the
information below is the National Research Counsel's Committee on
Infectious Diseases in Rats and Mice, Washington, D.C.; plus articles I've
photocopied over time out of veterinary & laboratory vivarium journals. I
tried to find some good stuff on the net to cite as well, but all I could
find were the amateur FAQ sheets that blame wire flooring exclusively &
fail to mention the actual cause (bacteria). Debbi Demarcan's book
acknowledges first the role of bacteria -- one of the rare cases of a lay
expert getting it right -- but then cannot resist carrying on about wire
bottoms & fails to mention that radical cleanliness, keeping the
environment dry, & periodically sterilizing surfaces to eradicate staph
are the actual preventative measures.

Since the actual culprit is a bacteria, it is contageous in its early
stages. Careful studies in guinea pigs & rabbits have shown that wire
cages DO NOT cause bumblefoot & the incident of outbreak does not increase
with animals living on wire cage floors than those living on wooden floors
or amidst shavings. The exception is a single study in which animals kept
on RUSTY abrasive wire had a SLIGHT statistical increase in
pododermatitis; the rust harbors bacteria & the roughness of the rust
abrades the feet. Filthy, moist shavings are even more apt to harbor the
bacteria meaning cages without wire floors, but not kept dry & clean, are
the greater danger.

However, once the bacteria is established in the foot, all feeling in the
foot is lost. Injury & reinjury will hasten the progress of the disease.
Wire provides no protection for the foot, especially if the animal is
overweight or prone to leaping about while no longer able to tell how much
pressure it is putting on its own feet. An animal that already has
pododermatitis may therefore be at risk of further injury living on a
wire-bottomed cage.

The infection will in time cease to be contageous but leaves the foot with
a sort of leprosy that persists for the life of the rodent. Thus rats no
longer in the early active phases of bacterial infection, but in the later
stages of permanent soarhocks, do not need to live separate from other
rats.

Pododermatitis is "multi-factorial in etiology" to quote the veterinary
jargon, meaning ANY claim of a single cause won't always hit the mark in
all species or in all outbreaks. It's sometimes caused by virus
infections, occasionally by fungus infection, & often in tandem with one
or another myco bacteria, inducing papuals of the foot, not painful but
disfiguring.  Bacterial pododermatitis in farm animals has been
effectively prevented with vaccines but no one is working on a rat vaccine
equivalent. The bacteria is known to harbor in dirt & feces, suggesting
that rats' capacity to walk in their own feces is a contributing factor
that can be LESSENED by a wire floor. Usually present in afflicted rats is
staph infection, which is HIGHLY contagious, & apt to occur in filthy
cages of any stripe. But some papers admit an uncertainty that Staph is
the root cause which may instead be Myco (which does not harbor
exclusively in the lungs & can cause foot lesions & arthritis) and/or
viral, but the overt contagion is nevertheless most commonly staph.

Some diseases including those associated with Pododermatitis are unevenly
dispersed regionally. A Japanese study tracked one outbreak to an original
entrypoint in Japan, but it has since spread. It means there might be
outbreaks in, say, Flagstaff & appear to numerous ratkeepers with a
similar cause & outcome; but the experience of alarmed Flagstaffers will
have no baring on rat owners in, say, Seattle if it is not the same mix of
cause or disease strain. This is also why in some areas the disease is not
seen at all while in other regions bumblefoot is extremely common.

Pododermatitis is usually the outcome of a long period of systemic
depletion of the immune system coming in the aftermath of other illnesses,
or from general poor care or poor diet, or from undetectible subclinical
infections that are not so connected to quality of care (subclinical myco
for instance). Wet litter is the single most important factor -- staph can
harbor almost indefinitely in wet litter waiting for some foot injury to
tramp by. Obesity is also a factor, not necessarily (though possibly yes)
because of the extra weight of the animal but because obesity is a sign of
the ongoing improper care that has been wearing down the immune system
long before Pododermatitis erupts. The greater implication is that correct
diet & exercise is a preventative; whoever lets their rats get overweight
are probably doing much else wrong as well, diminishing their rats' immune
system.

I could find no controlled study on cage effects on rats per se, but there
are a handful of comparative studies for rabbits & guinea pigs, & scores
of studies on small caged livestock. A 1996 article by Rommers & Meijerhof
reported on a controlled experiment to see if actual outbreaks of
bacterial "soar hocks" was greater for rabbits on wire than on slats or on
synthetic mesh. They detected a marginal difference in favor of the wood
but did not regard it as so significant as to justify changes in
rabbitries (most of which place rabbits on wire-bottomed cages), and the
disease occurred in all cage types (they did not test glass). The
synthetic mesh was wire-like, by the way, without even the slight
statistical numbers against it.  Guinea pig studies (i.e., Ishihara, 1980)
indicate that Staphylococcus aureus is aggravated by RUSTED wire cages,
not otherwise with wire; I was reminded of the widespread sentiment that
if a kid falls on a rusty nail he risks blood poisoning because animal
urine adheres to rust, but punk rockers pierced themselves with clean
unrusted nails without fear.

Some studies are not conclusive, but none really condemn a clean
wire-bottomed cage when scientific eyes are applied to the situation. Some
authors (Besselsen, 1993, on cavies) do not suggest wire cages are a
hazard unless "rough & soiled" but does say the wire cage will increase
the problem AFTER a bacterial staph infection has erupted so that the
animal must live thereafter on a wooden floor kept scrupulously dry.  A
foot injury NOT caused by infectious lesion will heal in the manner of
normal wounds but those in which staph was transiently harbored will have
irreversible leprousy-like aftereffects of swollen disfigurement & loss of
feeling in the foot or feet. Aggressive antibiotic treatments & radical
cleanliness will clear up the infective agent & stop the rat from being
infectious to its fellow rats, but the harm done the individual animal is
for life.

-paghat the ratgirl