The Science

An abscess is a localised pus-filled cavity surrounded by inflamed tissue.

It is usually caused by a puncture wound from bites or some similar trauma and already existing infections. The surface of the wound heals over, trapping the bacteria inside. The body's own defence mechanism kicks in (the white blood cells) to fight the invading infection, killing the cells and forming what eventually appears on the skin's surface as the pus filled swelling.

If the abscess if left unattended to or develops deeper inside, spreading the infection through the blood, blood poisoning may occur.

Common areas for bite wound abscesses include the facial cheeks, the legs, belly/back and the base of the tail.

Abscesses can be caused by many different aerobic bacteria and anaerobic bacteria.

  • Cervical - Klebsiella pneumoniae, Pasteurella pneumotropica, Streptococcus pyogenes
  • Facial, orbital, and tail - Staphylococcus aureus
  • Preputial gland - Pasteurella pneumotropica, Staphylococcus aureus
  • Kidney - Corynebacterium kutscheri, Klebsiella pneumoniae
  • Liver - Bacillus piliformis (Tyzzer's Disease), Corynebacterium kutscheri, Klebsiella pneumoniae
  • Lung - Cilia-associated respiratory bacillus (Car Bacillus), Mycoplasma pulmonis
  • Mesenteric lymph nodes - Klebsiella pneumoniae


  • A pus filled swelling
  • A smelly, draining, sore if the abscess HAS ruptured
  • A wound that is not healing
  • A tender area - You may only find a tender area and possibly notice the odour characteristic of deep infection.
  • A more internal abscess will not show through the skin, but other symptoms may arise, from anorexia, lethargy, weight loss to organ system dysfunction


  • Removal of some the the fluid with a fine needle, or bursting of the abscess and pus coming out.
  • Biopsy, histopathologic examination and culture
  • Gram staining


If the abscess appears small and ready to open, placing hot compresses on it for short periods of time may speed up the process, whereby the abscess can be cleaned and drained.
Once the abscess is drained, it will need to be kept clean, possibly with more draining involved (may take quite a few attempts to get all the infection out). Try preventing the abscess from closing over before it is completely drained, or the whole process may start over again.

For larger/deeper abscesses, lancing may be required by your Vet. Once open, it will need to be flushed clean on a regular basis. You may have to try and keep the abscess open and squeeze out any remaining pus then clean with disinfectant at home (saline solution of approx 5 g salt in
500 ml water is good for this). If the abscess is large or especially painful, sedation may be required to accomplish this.

Antibiotics may also be administered to help prevent recurrence of the problem. They may also be used for larger abscesses when surgery is an unlikely option (eg. the rat also suffers severe respiratory problems and surgery would be risky). The antibiotics will NOT clear the abscess, but will at least keep it down and help prevent the infection from spreading. Ideally, abscesses should first be cultured to determine the best choice for antibiotic treatment.


Try to prevent fighting between rats, where biting is concerned. Keep cages clean. Treat all signs of wounds promptly, especially if infection is suspected.