Michel Gruaz, with Esther van Praag, Ph.D.
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In past times, when a rabbit developed a large sized abscess on the cheek, the cause was believed to be bovine hypodermosis or warbles caused by the larva of the ox warble-fly Hypoderma bovis. Lumps (sterile abscesses) on the back of cattle or deer contain young warbles/larva. The presence of a facial abscess should, however, be taken seriously. Main causes are dental problems and bacterial infections like staphylococcosis and pasteurellosis.
An abscess is a pocket of fluids and pus that results from an attack by pyogenic organisms (bacteria that produce pus), followed by cell destruction. The content consists of pus, dead phagocytic white blood cells, necrotic cells and dead or living bacteria. The pocket grows in size when the amount of pus increases. During the encapsulation phase, the abscess gets isolated from the surrounding tissues and blood circulation. If the abscess is not treated, it can burst to the inside or at the surface of the skin. Bacteria and their toxins will be released in the blood, which is life-threatening (septicemia, which is difficult to treat in rabbits) and painful.
Many rabbits suffering from abscesses have a history of pasteurellosis or infections caused by other bacteria, e.g., Streptococcus sp., Pseudomonas sp. and/or fusiform – spindle shaped bacteria. The development of jaw abscesses may have a genetic origin (malocclusion, abnormal elongation of a molar), but can also relate to apical (tooth root) problems due to dental trauma (fracture) or to the presence of a foreign body such as a piece of hay stuck between molars. Bacteria can enter the space between the gum tissue and the tooth and reach the dental root. Often Staphylococcus sp. or Pasteurella sp. bacteria are isolated, but Fusobacterium sp., Actinomyces sp. or Streptococcus sp. (which can infect humans teeth) may be the cause as well.
No specific clinical signs are linked to the presence of an abscess. In a primary stage, it is possible to feel a lump or a bump along the bone of the mandibular jaw. Abscesses can feel hard or as a soft paste like lump that can be moved. Their presence does not appear to cause pain in rabbits, unlike observed in other animals. Growth of abscesses is usually fast, and their size can double within a few days.
This stage is often overlooked the rabbit continues to eat normally. Then, gradually, an unusual limp appears, accompanied by a reduced appetite, increased drinking and sometimes fever.
Identification of the problem - diagnosis
If the visual examination and palpation of head conclude to the presence of a maxillary or mandibular abscess, the oral cavity of the rabbit must be carefully examined. This is best done on a sedated or anesthesized rabbit.
The anesthesized rabbit is immobilized to avoid any movement that could blur the images. Ideally, radiographs are taken from different angles (ventrodorsal, lateral et oblique). Images must be of irreproachable quality, high resolution when available. In order to provide information of the dental problem such as e.g., bone deformation, root-related problems, presence of abscesses, and spread of the infection to the jaw bone. Computed tomography (CT scan) can help refine diagnosis, e.g., by locating the dental problem precisely and image its extent, evaluate prognosis and predict therapeutic outcomes.
The jaw bone can get infected. A sample can be aspirated in a syringe with a needle of smaller gauge and sent to a specialized laboratory. Unfortunately, it happens that diagnosis comes back with an incorrect diagnosis such as osteosarcoma (tumor of the bone, rare in rabbits) instead of dental abscess with bone infection (osteomyelitis). This mistake can have disastrous consequences, delaying proper treatment and administration of antibiotics.
Treatment of a facial abscess is difficult and long, and requires cooperation and dedication of the owner for post-surgical care. Recurrence is frequent.
If the lump can be felt, but is small in size, an antibiotic treatment can be attempted. In one case, the rabbit had lost a tooth, and the cavity was filled with pus. The combined administration of daily marbofloxacin and weekly injection of long-acting penicillin cured the problem. If the rabbit presents sensitivity to penicillin, this antibiotic can be replaced by e.g., metronidazole. The use of systemic antibiotics is, however, not always efficacious and a more aggressive approach is necessary.
The safest approach is full excision of the abscess capsule and of surrounding infected and/or necrotic tissues. During the surgery, it is important to verify that all fibrous channels leading to abscess cavities located deeper in the tissue are removed. If those pockets cannot be removed, they should be flushed with an antiseptic solution (chlohexiderme or povidone iodine) by means of a catheter. The debrided cavity can be filled with products impregnated with antibiotics. Another option is to place a drain to facilitate post-surgical care and help healing.
If surgical excision is not possible, the abscess pocket should be carefully debrided. Every trace of pus, of tooth or bone fragments, or of necrotic tissue should be removed to promote a good healing. The pocket can be filled with PMMA beads impregnated with antibiotics, with cellulose-based sponges or calcium hydroxide, before the incision is sutured. Details about fillings can be found here: Skin abscess in rabbits. Another option is to keep the wound open by suturing the edges of the incision to the skin (marsupialisation). This enables an “easy” daily care, such as flushing with chlohexiderme or povidone iodine or filling with products that dry out the cavity (e.g., dextrose, medical honey, manuka honey). During the healing process, the cavity will progressively fill with scar tissue and heal.
If osteomyelitis, its extension in the jaw bone must be assessed. If the infection spreads over a few molars, prognosis is guarded and the option of humanely putting the rabbit to sleep should be considered. Treatment includes the administration of systemic antibiotics that penetrate the bone, chosen according to the results obtained from the bacterial culture and antibiotic sensitivity tests. The choice of antibiotics safe to use in rabbits is limited. The treatment must be aggressive and long, between 4 to 6 weeks. If the antibiotics fails to reduce the infection, or bone has been destroyed, surgical debridement should be considered.
It must be taken into consideration that abscesses are often difficult to treat and healing cannot be 100% guaranteed. Post-surgical follow-up are, therefore, recommended.
A big thank you to (alphabetic order) Caroline Charland (www.BunnyBunch.org), to Michel Gruaz (Suisse), to Debbie Hanson (USA) and her rabbit Stella, to Dr. Cheryl Morales (Prestonwood, Houston, TX, US), to Bonnie Salt (USA), to Tal Saarony (USA) and her rabbit Motek, to Dr. Gil Stanzione (Dakota Veterinary Clinic, White Plains, NY, US), to Jen Smuck (USA), and to Akira Yamanouchi (Veterinary Exotic Information Network, Japan) for the permission to use their pictures.