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Abscesses in Rabbits - Dr. Carolynn Harvey
Abscesses in Rabbits
Bunny Fest 2010
Carolynn Harvey, DVM

Recognizing an abscess
An abscess is a collection of pus surrounded by fibrous or inflamed tissue. Pus is a thick material composed of white blood cells, dead tissue and microorganisms. When on the surface of the rabbit, abscesses feel like lumps or growths. When they are internal, they are sometimes detected by the problems they cause. For example a mouth abscess can cause drooling or difficulty eating or an abdominal abscess may cause colic (abdominal pain) or septicemia (releasing bacteria into the blood stream).

Causes of abscesses:

  1. Sterile abscesses: are pretty rare. They occur when foreign material gets into the body and causes the immune system form pus to try to remove it.
  2. Puncture wounds
  3. Puncture wounds
  4. Puncture wounds - a common cause. Anything that puts bacteria below the surface of the body can form an abscess. Bite wounds, catclaw wounds, non- sterile injections, oral or intestinal pokes from sharp ingested items. Take-home lesson: take puncture wounds seriously. You cannot do an adequate job cleaning these at home, they close up too completely. Always use sterile supplies for injections.
  5. Blood borne bacteria (may settle out anywhere bacteria like to grow, like the tooth root area, lung or chest). The source can be internal (normal GI bacteria) or external (wound, respiratory infection, ingested).

Approaches to diagnosis:

  1. Physical exam - may be enough
  2. Fine needle aspirate or biopsy
  3. Radiology - includes (in order of cost) x-rays, ultrasound, CT scan, MRI
  4. Culture - if the abscess is accessible, a culture may be done to find out which antibiotics are most appropriate. Unfortunately, rabbit pus grows poorly in culture, so results are often negative when pus is cultured. Culturing solid tissue like abscess capsule or tooth or bone yields better results. Ideally, the culture , should be done before any antibiotics have been given, but this is sometimes not practical. Some veterinarians like to stop antibiotics before surgery to improve the chances of a good culture.
  5. Exploratory surgery

The details of an individual abscess may dictate the best treatment and the chance of cure.

  1. Thickness of capsule: A thick capsule is good because it contains the bacteria best and makes spread of infection less likely. It's bad because it blocks delivery of antibiotic into the center of the abscess. Abscesses with thin or incomplete capsules are not good candidates for flushing because the flush may escape the capsule and spread infection.
  2. Location: Superficial (surface abscesses) not attached to underlying tissue can often be cured by surgically removing them as if they were a tumor. Large abscesses or surface abscesses that also involve deep structures may defy complete removal and need to be opened and "marsupialized", creating a pocket that can be cleaned out over several weeks. Severe abscesses on extremities (ear, leg, tail) sometimes are cured with amputation of the extremity. Internal abscesses (in the chest, in the abdomen) may or may not be surgically removable, depending on what issues are involved. Radiographs (x-rays) or a CT or MRI scan can be very helpful in planning surgery, by showing the extent of the abscess.
  3. Type of Bacteria: Sometimes we know this from culturing the abscess. Sometimes we have to guess by knowing what kinds of bacteria are common in that kind of abscess. The type of bacteria will determine which antibiotics are appropriate, and influence the plan for surgery and aftercare. Pasteurella is just one kind of abscess-forming bacteria. In large colonies of rabbits, it often causes "herd problems". It is not the only or even the most common abscess bacteria seen in pet rabbits.
  4. The patient: A young, healthy rabbit needs a different approach from a senior rabbit with many on-going health concerns.

Why are Rabbit abscesses different?

  1. Rabbit immune system: good at walling off bacteria but poor at killing them
  2. Rabbit pus is often thick and cheesy and doesn't allow good results from flushing and draining.
  3. Rabbits don't tolerate all the antibiotics we use in other species.
  4. Rabbits are sensitive to stress. Stress of illness, surgery, and medication suppresses the immune system and makes healing harder.
  5. Rabbits' teeth grow throughout their life, making the tooth roots a nutrient-rich protected site, ideal for bacteria to grow.
  6. The rabbit's fermenting GI tract harbors lots of bacteria that grow without air, and these survive well in deep abscesses, such as tooth roots

Options for treatment

  1. Medication alone: rarely cures abscesses. May be appropriate to try in the early stages, or while waiting for an abscess to be better walled off to increase chance of surgical cure.
  2. Surgical excision; "cut it out" - works when the abscess is well walled-off, easily accessible and doesn't involve vital structures.
  3. Lance and drain: rarely cures large, deep abscesses or those involving teeth or bones. May control a large, multipocketed abscess, or an abscess in a patient that's a poor surgical candidate.
  4. Marsupialization: means surgically creating an open pocket to allow the abscess to be cleaned out (flushed or curetted) until all infected tissue is removed and it is allowed to heal.
 
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