Abscesses in Rodents

Abscesses in Rodents

An abscess is a focal accumulation of pus in a cavity formed by degenerating tissue. Abscesses form when infectious agents (bacteria, fungi or parasites) or foreign bodies lodge in tissue and cause a persistent inflammatory response. Abscesses can form in any tissue in the body and the clinical changes are determined by their location and the pressure they exert on nearby organs, the degree of toxemia that they create from their bacterial content, and the amount of tissue destroyed.

What to Watch For

  • Swelling
  • Redness
  • Signs of focal irritation
  • Excessive grooming
  • Itchiness
  • Discharge
  • Moistened fur
  • Firm, painful mass
  • Drooling
  • Persistent bad breath
  • Facial swelling
  • Depression
  • Loss of appetite
  • Weight loss

    Seek veterinary care immediately if a mass is noted, the mass suddenly disappears and the animal becomes acutely depressed or lethargic.


    Abscesses are easily diagnosed by finding pus on fine-needle aspiration. In addition, your veterinarian may want to do the following:

  • History and physical examination
  • Complete blood count
  • Blood chemistries
  • Cytology (microscopic evaluation of cells)
  • Biopsy and microscopic evaluation of affected tissues
  • Culture and antimicrobial sensitivity testing
  • Radiographs (X-rays)
  • Ultrasound


  • Surgical removal of affected tissues
  • Surgically opening and flushing the abscess
  • Systemic and local antimicrobial agents
  • Fluids and supportive nutrition

    Home Care

    Keep infected rodents in isolation during treatment. For skin abscesses, make certain that the abscess remains open so it will heal from the inside to the outside.

    On a daily basis, monitor fecal and urine output to assure proper food and water consumption and digestion, and monitor weight daily.

    Preventive Care

    Prevention is the best cure. Keep sharp objects away from your rodents, and keep your rodent's living area clean and sanitized. You should also avoid contact between rodents that may result in puncture wounds from teeth or nails.

    Prevent your companion rodent from chewing on sharp or fibrous objects that may cut the gums or inside of the mouth or that may splinter and cause penetrating wounds in the mouth. If your companion rodent is scratched or cut, see your veterinarian as soon as possible so the wound can be properly cleaned and treated.

    Abscesses form when invading infectious agents (bacteria, fungi, parasites) or foreign bodies (like splinters) lodge in tissue and cause a persistent inflammatory response. As part of the body's defense mechanism the immune system stimulates the production of cells and secretions that attempt to "wall off" and destroy invading organisms or foreign bodies. It is a wall of fibrin that creates the borders of an abscess. Abscesses are typically filled with a creamy material that is usually whitish, yellowish, greyish, or brownish in color. This creamy material is called pus and is formed by the body's attempt to liquefy and remove dead or dying cells. Some abscesses may contain blood or be blackish in color from degenerating blood cells.

    Cysts, tumors, hematomas, fibrous scars and granulomas can cause swellings that appear similar to an abscess. Bot fly larvae may cause swollen areas in rodents housed outdoors.

    In rodents, abscesses of the tail and area around the anus are particularly common because of frequent bite wounds to these areas. Staphylococcus, streptococcus, pasturella, E. coli, corynebacterium, Pseudomonas actinobacter, klebisella and Mycobacterium avium have all been associated with abscesses in rodents. Any foreign body, bacteria, fungus or parasite that can encyst as part of its life cycle could cause an abscess.

    Abscesses can form in any tissue in the body like the skin, muscle, walls of blood vessels, liver, lung, heart and brain. The clinical changes that might occur vary with the location of the abscess. Abscesses in the skin will either become encapsulated and slowly resolve, migrate internally, which may lead to septicemia and death, or migrate externally allowing the pus to be released from the body. The material contained within an encapsulated abscess may be slowly absorbed to a point where only a small knot remains as evidence of the former abscess. Abscesses in internal tissues will either become encapsulated and slowly resolve or will rupture. When these internal abscesses rupture, the immune system either cleans up the released debris or this material can cause septicemia, which can be fatal. Infections that originate in the middle or internal ear, tooth roots, bone, heart, lungs or nasal sinuses may spread to and cause abscess formation in the brain, which are particularly dangerous.

    Abscesses involving the skin, tissue around the eyes or lining of the mouth are recognized by swelling, redness, heat or signs of focal irritation or pain. A deeper abscess should be considered in animals that excessively groom or constantly scratch at the same area. The sudden moistening of fur with a thick creamy discharge that is usually malodorous might indicate that a deep abscess has recently ruptured. If this clinical change is noted, seek veterinary attention as soon as possible so that any deep tissue damage can be treated and any infectious material that may still be present in the deeper tissues can be removed.

    Abscesses in the lining of the mouth or associated with the teeth may cause excessive salivation and persistent malodorous breath. Abscesses in the back of the mouth may be associated with difficulty swallowing or difficulty breathing.

    Abscesses associated with bacteria and fungi can be life threatening if not treated appropriately and in a timely manner. If the body is not successful in walling off an infectious agent, then the site of a persistent bacterial or fungal infection can be a center for producing millions of infectious organisms (or large quantities of toxins from the infectious organism) that can enter the blood stream and seed infections in other organs or cause system failure and death. Seek veterinary care immediately if a mass is noted, the mass suddenly disappears and the animal becomes acutely depressed or lethargic. These changes could indicate that an abscess has ruptured with the toxic material contained in its center is being released to the blood stream.

    In well-walled of abscesses, the rodent may be clinically normal with no recognizable changes in attitude or blood values. If an abscess is discharging a portion of degenerated cells to the blood stream, then the rodent is likely to be feverish, depressed and have an elevated white blood cell count. These clinical changes are similar to those associated with many bacterial, fungal or viral infections.

    Infections are most common in crowded conditions where numerous rodents are being congregated.

    Diagnosis In-depth

  • Your veterinarian may use radiographs (X-rays) or changes in the types of blood cells (CBC) or enzymes found in the blood (blood chemistry) to evaluate the overall health status of a sick rodent. The most common radiographic change associated with an abscess is a soft tissue mass in the affected tissue. Radiographs may be used to determine if the abscess is associated with an underlying bone (requires more aggressive and longer therapy), joint or internal organ or if the abscess is undergoing calcification. Radiographs may be helpful for determining if a foreign body is the cause of an abscess. Cysts, tumors, hematomas, fibrous scars and granulomas can appear radiographically similar to an abscess. Ultrasound may be used to determine if a mass is fluid-filled or solid and to determine if a foreign body is present in the mass.
  • If the abscess is completely walled-off by the immune response, then there may be no changes in the white blood cell count. If the abscess has recently formed or is leaking infectious agents to the general circulation, then there may be a substantial increase in the number of white blood cells (neutrophilia) with or without toxic changes in these cells. In rodents that are septic, the white blood cell may be decreased (neutropenia) with a high proportion of immature cells and/or toxic changes. This finding is associated with a poorer prognosis.
  • Confirming the cause of an abscess is best achieved by combining tests that demonstrate the morphologic characteristics of an organism (cytology or biopsy) with culture and antimicrobial sensitivity. Culture is usually necessary to specifically identify the type of bacteria or fungus present in the organism, but cultures from abscesses are frequently negative. Cytology is important in helping to identify the presence of organisms that may be difficult to grow in the laboratory. Cytology and culture of fluid collected from the spinal canal (CSF tap) may be used in rodents with suspected infections in the brain or nervous system.

    Therapy In-depth

  • Complete surgical excision of an abscess is best if all of the affected tissue can be removed without causing problems in the rodent. If excision is not possible, then as much affected tissue as possible will be surgically removed and the wound will be left open to facilitate flushing and healing from the inside to the outside. Depending on the type of rodent and the location of the abscess, your veterinarian may or may not place a piece of tubing (called a drain) in your animal.
  • Both local and systemic antimicrobial agents will probably be prescribed for your rodent. Depending on ease of administration your veterinarian may suggest an injectable or oral antimicrobial agent. Long term antimicrobial therapy may be necessary, particularly with fungal infections or when bone is involved.
  • Local abscesses will probably be treated on an outpatient basis. Rodents with septicemia or with abscesses involving internal organs will probably be hospitalized for the initial treatment period.
  • Spaying will probably be recommended in a female with an abscess of the uterus. Castration will be recommended if a testicle is abscessed. Abscessed teeth will be removed.
  • Other therapies that may be needed include fluids to correct dehydration and supportive nutrition if the rodent has not eaten for several days or has lost considerable weight.
  • Treatment is considered successful when a rodent is removed from antibiotics and remains clinically normal.

    Optimal treatment for your companion rodent requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your rodent does not rapidly improve.

  • Make certain you administer all prescribed medications at the appropriate time intervals. Contact your veterinarian immediately if you are having difficulties treating your animal as prescribed. If you are having problems, it may be best to hospitalized your rodent to assure that a proper course of treatment is administered.
  • Rodents that are being treated for abscesses should be isolated from other animals to prevent transmission of infectious agents.
  • For skin abscesses, make certain that the abscess is staying open so it will heal from the inside to the outside. If a surgically opened abscess closes over, contact your veterinarian immediately.
  • Clinical changes associated with an abscess should begin to improve within 24 to 48 hours after the abscess has been surgically opened and antimicrobial therapy has been initiated. If your rodent does not respond within this time period, you should contact your veterinarian. As the abscess heals, it should begin to decrease in size, drainage should decrease, inflammation should decrease and the animal's general condition should improve.

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