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Understanding Abscesses In
Rabbits
From the
Rabbit Welfare Association website
What is an abscess?
An abscess is a walled-off pocket of infection, which
contains infecting bacteria, in order to stop them spreading
throughout the body - a potentially lethal situation.
They are fairly common in pet rabbits and can occur
anywhere in the body. Common sites include the skin
(after injury or surgery) or in the head and neck, frequently
secondary to dental disease.
What do abscesses
do?
To understand the process better, let's take a look
at how a typical abscess is formed. Imagine a rabbit
with a small bite wound - please don't try this over
lunch!
The presence of bacteria multiplying in the wound sends
signals to the body's immune system. Cells of the immune
system respond like the cavalry, approaching the infected
area from all directions and surrounding it. The bacteria
may continue to multiply and cause damage up to a point,
but most of their food and oxygen supply will be cut
off. The bravest of the immune cells invade the area
in a kamikaze act and the majority of bugs will be killed
off in the ensuing battle. The point is eventually reached
where the centre of the battlefield consists of dead
bacteria, immune cells and neighbouring tissue which
disintegrates to form the creamy liquid which we know
and love as pus!
Meanwhile, the surrounding tissue and remaining immune
cells band together to form a wall, or capsule - a highly
effective blockade which prevents further spread of
any remaining infection. Unfortunately, a few bacteria
usually manage to adapt and survive cocooned in the
thick wall of the abscess where the immune system cannot
get to them. These bugs are than able to lie dormant
until an opportunity arises for them to reactivate.
Over time, fluid build-up inside the abscess cavity
increases the pressure within until the abscess bursts,
expelling pus and bacteria out of the body where it
can do no harm. This is usually the best option for
the rabbit: indeed "letting out the pus" forms
the basis for successful treatment. Under certain circumstances,
however, this can go disastrously wrong. For example,
if an abscess in the gut wall bursts into the abdominal
cavity, the consequences can be devastating: bacteria
may escape and multiply causing overwhelming infection
before the immune system has a chance to contain it.
Abscesses that don't burst can remain in status quo
for many months or years with no ill effects to the
rabbit. Sometimes the remaining bacteria continue to
multiply slowly with an increase in abscess size, but
any deterioration in the rabbit's health or nutritional
status may allow large numbers of bacteria to build
up and eventually overpower the local defence mechanisms
and escape to cause widespread infection.
One particularly unpleasant scenario that sometimes
occurs is when the bacteria that have escaped settle
in different locations around the body and cause new
abscesses to form. This is called "seeding"
and the doses of antibiotics required to penetrate multiple
abscesses that cannot be reached surgically would cause
the rabbit major side effects without much hope of success.
Sadly, the only humane option if this occurs is euthanasia.
It's not just trauma (e.g. bites and scratches) that
can cause abscesses to form. "Foreign bodies"
can help bugs hitch a ride through the skin and initiate
formation of an abscess. Foreign bodies include grass
seeds and sutures left after surgery - which is why
it is important to remove non-dissolving sutures once
a wound has healed, and to check that the dissolving
type break down and disappear over time.
How are abscesses
treated?
Treatment will vary depending on the site and underlying
cause of the abscess, but there are certain basic principles
which apply to them all.
The Basic
If an abscess is anything other than small and superficial,
the rabbit will need sedation or general anaesthesia
so the abscess can be thoroughly probed and cleaned
out. The subsequent treatment may also cause significant
discomfort, so the bunny will need prolonged and adequate
analgesia. Vets may need to be reminded to supply pain
relieving drugs for use between visits, but most will
offer it automatically.
The first step is to get rid of the pus. The abscess
cavity must be opened and drained, and the abscess wall
removed. Dead (necrotic) tissue often sticks to the
base of the cavity and must be removed (debrided). Even
scrupulous debridement is bound to leave some bugs behind,
so the importance of good wound care cannot be stressed
enough. If the skin over an abscess heals too soon,
bacteria will become trapped inside and reactivate,
and the whole cycle will begin again. Therefore the
wound cavity is often kept open (some have to be "packed"
to achieve this) until it heals from the inside. Daily
or twice daily cleaning of the wound cavity is a key
part of successful abscess treatment.
Many vets also give antibiotics. Systemic antibiotics
- given by mouth or injection - destroy any bacteria
that manage to escape into the body. Antibiotics can
also be placed inside the abscess cavity to kill off
any residual bugs from the abscess as well new ones
trying to get in from the outside. Many antibiotics
have difficulty gaining access to the bugs in the abscess
cavity itself which is why the recurrence rate is high
if the capsule isn’t completely removed.
Rabbit Pus
Rabbit pus is semi-solid and can be lumpy (a bit like
refined cottage cheese!) so it doesn't drain as freely
as in other animals. The most common bacteria involved
in rabbit abscesses belong to the Pasteurella species
and are accompanied by the strong smell of rancid milk,
hence the name.
The only way to be certain what bacteria are causing
an abscess is to do a "culture & sensitivity"
test (C&S). It's a good idea to obtain a C&S
when the abscess is drained. The sample should be taken
from the abscess wall to try and get some live bacteria
- those in the pus are usually dead.
Nursing care
Some rabbits don't seem too bothered by their abscesses
and carry on life as normal during treatment, but many
need careful nursing and supportive care. One specific
point is that clean, soft bedding is essential to reduce
the potential for contamination of the wound. Straw
and hay must be avoided. "Vet bed" is a comfortable
alternative which is easy to launder.
Abscesses Treatment
- Old and New
Over recent years, new weapons have been developed and
old ones rediscovered in the fight against abscesses.
Gels (e.g. Intrasite) help to stimulate
normal tissue growth and repair at the edges and base
of wounds. Some preparations also inhibit bacterial
growth and some newer preparations actually contain
antibiotic as a paste and can be used to pack the cavity
and left for longer.
Antibiotic solutions can be soaked into
gauze used to pack abscess cavities, but still need
to be changed daily. This method - applying relatively
high concentrations of antibiotic directly to the wound
- allows the use of antibiotics which would be toxic
if given systemically. Care still has to be taken, though,
because the drug may be absorbed into the body via the
wound which can upset the normal gut function of the
rabbit, which is dependent on friendly bugs which may
be killed off by the antibiotics.
Antibiotic beads: Some abscesses are
too deep and painful to clean every day, or are inaccessible.
Antibiotic impregnated beads can be packed into the
abscess cavity which is then sewn shut. They are left
there for anything up to a few months and provide a
slow but continuous release of antibiotic as well as
filling in the hole left by the abscess and preventing
it being filled by newly formed pus.
Dextrose: An ancient treatment coming
back into fashion is very strong dextrose (sugar) solution.
Normally, bacterial growth in the body increases as
sugar concentrations rise, because bugs use sugar as
a food source. This is why diabetic animals get more
infections. However, a 50% dextrose solution is so concentrated
that it not only inhibits the growth of most bacteria,
but actually kills them by sucking the water out of
them so that they die of dehydration. The dextrose can
also help draw out fluid that would otherwise accumulate
in the cavity. Dextrose solution is soaked onto gauze
and packed into the wound, filling the cavity. The dressing
must be changed at least once a day - otherwise fluid
coming out of the wound will dilute the dextrose, and
the dextrose may start to be absorbed into the body,
negating its beneficial effects.
Hyaluronidase may help to break up pus
and make it easier to remove.
N-acetylcysteine (Parvolex), also helps
break up pus and mucus, as well as stimulating some
immune functions and inhibiting certain aspects of bacterial
activity. It can be very effective, but smells rather
unpleasant!
Location and
Outcome
The site and size of the abscess often determine how
difficult the abscess will be to eradicate. Abscesses
on the foot or abdomen - subject to the pressure of
being walked or laid upon - will take much longer to
heal. Confining the rabbit to a cage or small, clean
area of flooring might help.
Abscesses around the tail are at high risk of contamination,
and other sites are subject to excessive licking, which
can contaminate the wound and prevent it from healing.
Abscesses developing close to the vital organs such
as the windpipe or heart can cause serious disease by
compressing these organs, and their position can make
surgical treatment difficult if not impossible.
If thing are
not going well
If an abscess that is being treated does not seem to
be getting better, your vet will ask him/herself a few
questions:
- Is there a residual foreign body preventing the
wound from healing completely?
- Was a hidden pocket of infection left behind (commonly
the case)?
- Has the abscess spread to underlying tissues such
as bone?
- Is there another problem going on which is helping
the infection persist?
- Has the right antibiotic been used at the right
dose for the right length of time?
- Is the rabbit getting what the vet has prescribed?
Rabbits that spit out their antibiotic may be better
treated with daily injections for a few days!
Despite all efforts, some rabbits do not survive their
abscess problems. Treatment failure is quite common
and often unavoidable due to the underlying cause; the
size and site of the abscess; the infecting organism;
and the general state of health of the rabbit.
The Bottom Line
Abscesses are common afflictions. Although they prevent
the spread of infection, they may themselves cause considerable
problems if not detected or dealt with promptly. Treatment
options have improved and the combination of aggressive
surgical intervention followed by fastidious wound care
can lead to the resolution of even rapidly enlarging
lesions.
By Dr Lucy Hansen
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