Abscesses in Rodents
Dr. Branson Ritchie
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.