Abscesses in Dogs

05 Jan 2018

Definition of an Abscess

An abscess is a localized pocket of pus contained in a walled-off cavity, usually just under a dog’s skin (although they can develop internally). Abscesses frequently are associated with scratches, bites, puncture wounds or other skin surface abrasions. Bacteria enter the site of the wound, multiply and start digesting the healthy surrounding tissue, causing inflammation and an infection. The byproduct of this process is the thick, yellowish substance commonly called “pus.” As they enlarge and harden, abscesses put pressure on nearby tissues and nerves and can be extremely painful, especially when they rupture. The infection can spread through the blood to other parts of a dog’s body, leading to systemic illness. This can cause a potentially life-threatening condition called “sepsis.” Owners should familiarize themselves with the causes and signs of abscesses, so that they can get treatment for their affected dogs as quickly as possible.

Causes of Canine Abscesses

Most abscesses in domestic dogs are caused by the invasion of healthy tissue by bacteria. Occasionally, abscesses are caused by fungal or protozoal microorganisms or even by parasitic worms, which are called “helminths.” One of the most common ways that dogs develop abscesses is when bacteria are inoculated under their skin through a bite wound, puncture, scratch, cut or other skin surface abrasion. The bacteria multiply inside the wound and start to digest and break down adjoining tissue. The bacterial infection is accompanied by an inflammatory reaction, which involves increased blood flow to the infected area, swelling, redness and pain. The by-product of this localized process, and the product of the digestion of dead and dying tissue, is a thick exudate commonly called “pus.” Pus is made up of white blood cells (leukocytes), a thin fluid called “liquor puris” and cellular debris. Eventually, the inflammatory process stimulates the creation of a fibrous capsule around the wound site, which is then called an “abscess”. If the accumulating pus is not reabsorbed by the dog’s body or otherwise drained out of the abscess cavity, it will put pressure on surrounding structures and can be extremely painful. Eventually, if left unattended, most superficial abscesses will rupture and drain on their own, which can be startling for unsuspecting owners and quite messy.

Diagnosis and Tests

Initial Evaluation

Most skin abscesses are easy to see, especially once they rupture and start to drain, but they may be difficult to detect in long-haired, heavily-coated breeds. Superficial abscesses are usually walled-off inside a protective fibrous capsule and feel firm, but somewhat squishy to the touch; at least before they rupture. Internal abscesses, such as those in the pancreas, lungs, liver or other organs, cannot be identified without more advanced techniques.

Diagnostic Procedures

A veterinarian presented with a dog with a visible skin abscess or draining tract usually will take a blood sample for evaluation. Because abscesses almost always involve a bacterial infection, routine blood work on affected dogs usually will identify infection. If the prostate gland has abscessed, a urinalysis will show the presence of pus and blood in the urine, which is never normal. If the liver or pancreas have abscessed, blood levels of liver enzymes or total bilirubin may be elevated, and circulating amylase/lipase levels may also be abnormal. A veterinarian can discuss the meaning of these various blood sample results with owners in greater detail.

Radiographs (X-rays) and ultrasonography can both be used to look for inhaled or ingested foreign objects and to assess whether any internal masses are fluid-filled abscesses or solid tissue tumors. Computed tomography (CT scan) and magnetic resonance imaging (MRI) are available at veterinary teaching hospitals and some specialty referral centers and can be particularly helpful to identify abscesses in the brain. Echocardiography, which basically is an ultrasound scan of the heart, can be used to diagnose cardiac abscesses.

One of the most common techniques for evaluating the cause of an abscess is to take several samples of the pus from its center and examine those samples under a microscope. The pus from an abscess usually is pale, pinkish or red. Sometimes, it will have a greenish tinge. The veterinarian may need to lance an external abscess in order to get a good sample of its contents, and also to help it drain and heal. Internal abscesses can be sampled by taking surgical biopsies. This involves sedating the dog and removing either a part of the abscess through an incisional biopsy or removing the entire encapsulated abscess throughan excisional biopsy. Most veterinarians recommend taking biopsies of both healthy and unhealthy tissue from the affected area. Many times, the veterinarian will use an ultrasound for guidance when taking biopsies of abscesses from internal organs. The sampled tissue will be sent to a laboratory for detailed examination by a veterinary pathologist. There are a number of different techniques that can be used to identify the precise active microorganisms that caused an abscess to form. Usually, some combination of bacteria is involved. It is important to figure out what type of bacteria caused the infection, so that a full course of appropriate antibiotics can be prescribed for the affected animal.

Symptoms and Signs

The symptoms and signs of abscesses may include one or more of the following:

Localized pain in the area of the abscess
Inflammation; redness; swelling at the abscess site
Heat at the abscess site
Lack of appetite
Lethargy
Fever
Licking or chewing at the abscess site
Saliva staining around the abscess site
Hair loss around the abscess site
Weeping, bleeding, oozing skin wound

More specific symptoms depend upon the organ system or tissue where the abscess occurs. For example, male dogs with prostate abscesses and dogs with anal sac abscesses often “scoot” their bottoms along the floor or ground in an attempt to relieve their discomfort. A lactating bitch with abscessed mammary glands will be noticeably tender, and her teats will be inflamed, hot, hard and red. She should not be permitted to nurse her puppies from any infected teats; newborns are highly susceptible to inhaling (aspirating) milk, which if infected with bacteria and pus, can quickly lead to serious respiratory illness, and possibly death.

As an abscess progresses and affected tissue deteriorates, the area may turn black and smell putrid. When a skin abscess ruptures, which they usually will do if not lanced, they typically drain a mixture of blood and pus and are messy and painful.

Internal abscesses are difficult to detect without special instruments. A dog with pulmonary abscesses may show progressive respiratory signs, such as coughing, difficulty breathing and noisy breathing, although there may be no outward signs suggesting that lung abscesses are the cause of the dog’s discomfort.

Treatment

Most external abscesses can be treated successfully on an outpatient basis. Only in very severe cases will in-patient hospitalization be necessary, such as in cases of mammary gland abscessation in a lactating bitch. Most veterinarians will lance obvious superficial skin abscesses to establish and maintain adequate drainage, followed by a course of broad spectrum antibiotics. Depending on its size and location, the whole abscess may be removed surgically, using local anesthesia, general anesthesia, or both. In either case, the entire area should be thoroughly cleaned and clipped, to identify the parameters of the abscess. In some cases, the attending veterinarian will place a temporary drain in the abscess to promote healing. This involves suturing a synthetic tube into the wound, to carry pus and other liquid away from the infection site. Other times, the abscess will be lanced, cleaned and left open to the external environment, to heal from the inside out. Hot packs can be applied to encourage drainage and relieve inflammation and pain.

Protective bandaging or collars may be necessary to keep the dog from bothering an abscess as it heals after treatment. Depending on the location of the abscess, the dog’s activity should be restricted until the draining resolves and the surrounding tissues are well on their way to returning to normal. Once the precise bacterial or other microorganisms responsible for the abscess are identified, appropriate antibiotic drug therapy should be started. Anti-inflammatory medications, such as non-steroidal anti-inflammatory drugs (NSAIDs), can also be helpful. If the infection has spread into the dog’s bloodstream, the situation is more severe. In that case, the dog has become “septic” and may need to receive intravenous antibiotics, fluids and in-patient supportive care.

Tooth root abscesses often are treated by pulling the affected tooth or performing a root canal. Lung, liver and pancreatic abscesses typically are treated by surgical resection of the infected area. Abscessed anal sacs can be removed in a fairly simple surgical procedure that involves removing the affected anal sac, called an “anal sacculectomy.”

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