Esther van Praag Ph.D.
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An abscess is a pocket of fluid and pus, which results from an attack by pyogenic organism (e.g., bacterium) followed by the destruction of cells. The pocket usually contains a collection of pus, dead phagocytic white blood cells, necrotic cells, and live or dead bacteria. Pus is particularly thick in rabbit; their heterophil cells (rabbit equivalent of neutrophils) contain a very low level of the enzyme myeloperoxidase, as compared in other animals (dogs, cats) or man. As a result, digestion and liquefication of the material contained in the abscess is slow and pus remains thick and sticky.
As the quantity of pus increases, the pocket grows larger and starts to wall off from the surrounding tissues and blood circulation. This renders treatment difficult. If the abscess is left untreated, it continues to grow. Tissue will rupture either inside the body or on the surface of the skin. This stage is dangerous, with the liberation of bacteria and their toxins in the blood circulation.
In most cases of abscess, the rabbit has a history of pasteurellosis, though other bacteria like Staphylococcus aureus, Streptococcus sp., Pseudomonas sp or Fusiformis sp. are no exceptions. They often result from a nasolacrimal or tooth problem, surgery, insect bites, scratches or skin wound, trauma, or a foreign body such as a hay splinter in the gum, foot sole or anal gland.
Abscesses are typically found on the head, neck and shoulders regions, but can also affect other parts of the body, organs or bones. During palpation, abscesses feel either as a hard lump or a soft doughy swelling that can be moved. The presence of an abscess is usually painless, unlike other animals. It is often observed that abscesses can grow within a few days time.
There are no specific clinical signs, except the presence of a lump, an unusual swelling, reduced appetite, increased water intake, and/or fever.
The treatment of an abscess is difficult, long, and recurrence is no exception in rabbits. Use of systemic antibiotics will have little effect and more aggressive therapy is needed.
The best option remains total surgical excision of the abscess cavity, necrotic tissue, and the surrounding fibrous capsule. This treatment can, however, not be done when several abscesses are present, or when the bone is affected (e.g., osteomyelitis, jaw bone infection by a tooth root). During the surgical procedure, it is important to check that no fibrous channels leading to abscess cavities deeper in the tissue remain. If present, the cavities must be flushed with antiseptic solutions (e.g., chlorhexiderm or iodine povidone) by means of a catheter tube. A drain can be placed to facilitate this procedure.
The cavity should be packed with an antibiotic impregnated dressing. Various types are available nowadays include:
• Permanent placement of antibiotic impregnated PMMA beads;
• Temporary filling with antibiotic impregnated gelatin or cellulose hemostat (e.g., GelFoam®, Surgicel®). The dressing must be changed daily or every 2nd day, to avoid necrosis of surrounding tissues;
• Temporary filling with wet-to-dry hygroscopic and bactericidal sugar dressing (e.g., 50% dextrose, or manuka or clear sterilized (g-rayed) honey). The dressing must be changed daily, to avoid necrosis of surrounding tissues.
The later filling presents the advantage to remove the malodorous smell of ammonium and sulfur compounds due to bacterial breakdown of serum or cell proteins.
If osteomyelitis (bone infection) has developed, systemic administration of antibiotics is necessary. Antibiotics of choice include those that penetrate the bone or joints, e.g., chloramphenicol, fluoroquinolone (enrofloxacin or marbofloxacin), bicillin (a combination of penicillin G benzathine and penicillin G procaine), or penicillinase-resistant semi-synthetic penicillin such as cephalosporin or metronidazole. The choice of antibiotics safe for use in rabbit is limited.
The treatment needs to be aggressive and long (4 to 6 weeks). If this antibiotic treatment is not successful, or if large parts of the bone have been destructed, radical debridement remains necessary. Nowadays, gentamycin PMMA beads can be implanted near the bone.
There is little information is available about the effusion rate of the antibiotic from antibiotic impregnated gel sponge or beads. Newly grown tissue may hinder a good distribution of the antibiotics from beads after 3 weeks already, limiting their action to 6 weeks.
It should be kept in mind that abscesses in rabbits are difficult to treat and a full recovery without relapse cannot be guaranteed.
Thanks are due (listed alphabetically) to Caroline Charland (www.bunnybunch.org, USA), to Dr. Orlando Diaz (Lake Howell Animal Clinic, Maitland-FL, USA), and to Michel Gruaz (Switzerland) for the gracious permission to use their pictures.
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