An abscess is a localized pocket of pus that is formed by the breakdown and disintegration of living tissue. Dog owners most commonly notice abscesses on or just under the outermost layer of their pet's skin, called the "epidermis." Skin abscesses are commonly associated with scratches, bites or puncture wounds caused by thorns, burrs, splinters, sticks or other penetrating objects, which provide a perfect environment for bacteria and other microorganisms to grow.
Some breeds, such as the Shar-Pei, English Bulldog and Labrador Retriever, are predisposed to developing abscesses between their toes, because their short, stiff hair shafts can get pushed back into the hair follicles, which become infected. Abscesses associated with ingrown hairs can be extremely painful. Pimples, boils, pustules and furuncles are all examples of small external abscesses. Larger intact abscesses feel like fluid under pressure to the touch, which is exactly what they are. Many times, abscesses will rupture and drain on their own. Other times, they need to be opened up (lanced) and drained by a veterinarian.
Not all abscesses are on or in the skin. They also quite often develop inside of a dog's body, such as in the chest cavity (heart, lungs), abdominal organs (liver, pancreas, stomach), prostate and mammary glands and anal sacs.
Causes of Abscesses in Dogs
Most abscesses are caused by the invasion of tissue by bacteria. Occasionally, they are caused by fungal or protozoal microorganisms, or even by parasitic worms, known as helminthes. One of the most common ways that dogs develop skin abscesses is when bacteria get inoculated into a bite wound, scratch, cut or other surface abrasion. The bacteria multiply inside the wound, forming a pus-filled localized cavity. Pus is a protein-rich by-product of inflammation, infection and bacterial digestion of dead and dying tissues. It is made up of white blood cells (leukocytes), a thin fluid called "liquor puris" and cellular debris. If accumulating pus is not reabsorbed by the dog's body or otherwise drained from an abscess cavity, it can put pressure on surrounding structures and be very painful. Eventually, left unattended, most superficial skin abscesses rupture and drain on their own, which can be startling for unsuspecting owners and quite messy.
Skin abscesses are the most common type of abscesses in domestic dogs, but abscesses can also develop internally. Other common sites of canine abscesses are anal sacs, prostate gland, mammary glands, brain, mouth and gums, tooth roots, pancreas, liver and lungs.
Prevention of Abscesses in Dogs
Skin abscesses can be avoided by preventing dog fights, cat bites and exposure to sharp, penetrating foreign objects. Superficial skin wounds should be cleaned and dried thoroughly, with the hair around the site well-trimmed, to make the area uninviting for bacterial growth. Anal sac abscesses, which are also fairly common in dogs, usually occur after the anal sac becomes impacted. They can be prevented by keeping the anal sacs clear and open through regular manual expression. This is probably best performed by a veterinarian as most dogs don't enjoy having their anal sacs expressed, and most owners don't enjoy the process, either. If a dog suffers from repeated anal sac impactions and abscesses, its owner may want to consider having those structures surgically removed by a veterinarian in a procedure called an anal saculectomy. Neutering male dogs will reduce their risk of developing prostatic abscesses, and spaying females will greatly reduce the chance of mammary gland abscesses and infection, a condition known as "mastitis." Abscesses in the mouth are best avoided by keeping dogs from chewing on dirty or sharp objects, such as sticks, stones, hangers, branches or nails. Lung abscesses can develop when a dog inhales plant material, especially foxtails or grass awns. Owners of dogs that spend lots of time outdoors should keep an eye on their noses and mouths. If they have repeated bouts of snorting and sneezing, especially during the Spring and Summer months, it probably is worth a quick trip to the veterinarian.
Fortunately, most superficial abscesses respond well to drainage, debridement and antibiotic therapy. While it is more difficult to detect and treat internal abscesses, it is still possible.
How Abscesses Affect Dogs
How an abscess will affect a dog depends largely on its location and size. Large internal abscesses can put pressure on nearby organs and tissues and can be extremely painful. However, even small or superficial skin abscesses can hurt a great deal, as anyone who has ever had an infected pimple can attest to. Dogs with skin abscesses often lick and chew at the affected area, which can exacerbate the pain and infection and cause trauma above and beyond the original injury. It also can cause the abscess to rupture.
Symptoms of Abscesses
Abscesses can cause a number of different symptoms, most of which are non-descript depending on their location and size. They include:
Localized pain in the area of the abscess
Lack of appetite (inappetance; anorexia)
Licking or chewing at the abscess site
Saliva staining around the abscess site
Hair loss around the abscess site
More specific symptoms depend upon the organ system or tissue that the abscess involves. For example, male dogs with prostate 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 even death.
As an abscess worsens and affected tissue dies and sloughs off, the area may turn black and smell putrid. When skin abscesses rupture, they usually drain a mixture of blood and pus and can be extremely messy.
Internal abscesses are difficult to detect without special instruments. For example, a dog with pulmonary (lung) abscesses may show progressive respiratory signs, such as coughing, difficulty breathing (dyspnea), noisy breathing and increased respiratory effort, although there are no outward signs pointing to lung abscesses as the cause of its discomfort.
Dogs at Increased Risk
Skin, mouth and lung abscesses are more common in outdoor dogs and those that participate in hunting or other competitive canine activities, because those dogs have more opportunities to come into contact with sharp, dirty objects and to inhale or swallow grass awns or other plant material. Intact dogs – especially free-roaming unneutered males – are at an increased risk of developing abscesses as a result of fighting with other animals, including dogs, cats, raccoons, skunks and porcupines. Older intact males, and in particular Doberman Pinschers, have a higher incidence of prostate disease in general, including prostatic abscesses. Intact bitches are more likely than spayed bitches to develop mammary abscesses.
Many skin abscesses are easy to see, especially once they rupture and start to drain. They can be harder to detect in long-haired, heavily-coated breeds. Superficial abscesses are usually walled-off and feel firm but somewhat squishy, at least before they rupture. Internal abscesses, such as those affecting the pancreas, lungs, liver or other organs, cannot be diagnosed without more advanced techniques.
Most veterinarians presented with a dog with a visible abscess or draining tract will take a blood sample and submit it to a pathology laboratory for evaluation. Because abscesses almost always involve a bacterial infection, routine blood work on affected dogs usually will reflect inflammation and infection. If the prostate gland has abscessed, a urinalysis will show the presence of pus in the urine, which is not normal. If the liver and/or pancreas have abscessed, blood levels of liver enzymes and/or total bilirubin may be elevated, and amylase/lipase levels may also be abnormal. A veterinarian can discuss the meaning of these various enzyme abnormalities with owners in greater detail.
Radiographs (X-rays) and ultrasound can be used to look for inhaled or ingested foreign objects and to assess whether any internal masses are fluid-filled or solid. 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 and assess abscesses in the brain. Echocardiography, is an ultrasound scan of the heart, can be used to diagnose cardiac abscesses.
One of the most common techniques for assessing an abscess is to take samples of from its center and examine them on glass slides under a microscope. The pus from an abscess usually will be pale, pinkish or red. Sometimes, it may have a greenish tinge. The veterinarian may have to lance an external abscess in order to get a good sample. There are a number of different stains that can be applied to the sample to identify the active microorganisms, which usually are some combination of bacteria. Internal abscesses can be sampled as well, by taking biopsies. Most veterinarians recommend taking biopsies of both healthy and abnormal tissue from the affected area. Many times, the veterinarian will use an ultrasound for guidance when taking biopsies of internal organs. The samples will be sent to a diagnostic laboratory for further examination and, probably, for bacterial culture and sensitivity. It is important to figure out what exact bacteria are involved in the infection, so that a full course of appropriate antibiotics can be prescribed.
Most external skin abscesses, such as those from dog or cat bites, penetrating foreign bodies, puncture wounds or other abrasions, can be treated successfully on an outpatient basis. Only in very severe cases will in-patient hospitalization be necessary, such as in severe cases of mammary gland abscessation. The overriding goals of treating abscesses are to clear up the infection and remove any identified objects that may have caused or contributed to the wound and infection in the first place.
Most veterinarians recommend lancing a skin abscess to establish and maintain adequate drainage and so that it can be cleaned. Depending on its size and location, the entire abscess may be able to be removed surgically, using either local anesthesia, general anesthesia, or both. 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. This involves suturing a synthetic tube into the wound, to carry liquid away from the infection site. Other times, the abscess will be lanced, debrided (cleaned out) and left open to the external environment, to heal from the inside out. Hot packs can be applied to stimulate drainage and relieve inflammation.
Protective bandaging or collars may be necessary to keep the dog from bothering the abscess as it heals. 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 bacteria or other organisms responsible for the abscess are identified, appropriate antibiotic drug therapy can be started. Anti-inflammatory medications 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 fluids and in-patient supportive care.
Tooth root abscesses often are treated by pulling the affected teeth 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.
The prognosis for a dog with an abscess depends on the location and size of the lesion, the degree of tissue death (necrosis) at the time of treatment, the severity of the infection and whether any critical organ function has been compromised. Anal sac abscesses, mouth abscesses and superficial skin abscesses are usually quite treatable on an outpatient basis and have an excellent prognosis for a complete cure. Unfortunately, if an abscess in the abdomen or chest cavity ruptures, the pus and infectious organisms will spill out and spread, causing a much more serious situation. Dogs with ruptured internal abscesses are predisposed to developing peritonitis, which can be life-threatening and carries a guarded prognosis.