Abscesses form as part of the body's response to infection or irritation. Essentially, they are pockets of pus that grow around wounds, irritants, or areas of infected tissue. Some abscesses may go unnoticed by a cat owner until they rupture and leak fluid. Knowing what to watch for and how to treat abscesses may save your cat's life. Untreated, abscesses can progress into life-threatening systemic infections.

What Is an Abscess?

An abscess is a pocket of pus, which is a thick fluid full of inflammatory cells reacting to an infectious organisms (like bacteria) or irritants. An abscess most commonly forms due to tissue infection. Abscesses can be found throughout the body (externally and internally) and can vary greatly in size.

Symptoms of Abscesses in Cats

Abscesses usually appear as a swelling under the skin, particularly in areas that are easily injured in a fight with another cat, but they can also occur in the mouth or inside the body cavity as well.

Abscesses look a lot like a tumor, but they appear more suddenly (often within days of the injury) and are tender to the touch. An abscess is full of fluid, so it will compress if touched and feel somewhat soft or squishy. Abscesses often swell to the point that they start oozing pus and/or blood from the entrance wound (a tooth or claw puncture, for instance). The fluid is often foul-smelling and can be tan to bloody in appearance.

If an abscess forms inside the mouth due to a tooth or gum infection, a cat may have notably bad breath, refuse to eat, and become lethargic. Abscesses inside the body may also cause lethargy and a decrease in appetite. Systemic infections caused by untreated abscesses can cause a cat to feel sick and develop a fever.

Causes of Abscesses

The most common types of abscesses in cats are in the mouth and under the skin, but abscesses can occur anywhere bacteria infiltrate tissue. Common bacterial culprits include E. coli, certain Streptococcus species, Pseudomonas, Mycoplasma, Pasteurella multocida, Corynebacterium, Actinomyces, Nocardia, Bacteroides, Clostridium, and Fusobacterium.

These bacteria are often introduced through wounds, injuries, or cavities that occur in various areas of the body, including:

• Dental abscesses: These abscesses are found at the root of diseased or damaged teeth. When bacteria accumulate on the surface of a tooth, the gums become inflamed and infected and abscesses can form under the gum line. If bacteria migrate into the root canal of a broken or diseased tooth, an abscess can form in this deeper tissue. Dental abscesses are common in cats but are difficult to notice until definitive signs like horrible breath, food refusal, or bloody saliva appear.
• Bite wound abscesses: In order for a cat to develop a bite wound abscess, it needs to be bitten by another animal. This is why bite wound abscesses are most common in cats that spend time outdoors. When a cat gets bitten, bacteria from the other animal's mouth enter the wound and an infection can form. These are seen under the skin of cats as lumps and usually aren't noticed by the cat owner until they rupture and begin to ooze pus. These abscesses may feel hot to the touch as well as cause skin inflammation.
• Internal abscesses: Invisible from the outside of a cat's body, internal abscesses occur on internal organs from inflammation, disease, and foreign objects. These are far less common than bite wounds and dental abscesses.

Diagnosing Abscesses in Cats

If your veterinarian suspects a skin abscess from a bite wound or other injury, and the abscess has not ruptured, then a fine needle aspiration (FNA) may be performed to see what is inside. If it is an abscess, your vet will be able to draw pus into the syringe.

If a dental abscess is suspected, a veterinarian will examine the cat's mouth for evidence of pus, but anesthesia and X-rays will need to be performed to thoroughly inspect the mouth. Abscesses will show up on X-rays and will needed to be addressed surgically while the cat is under anesthesia.

If an internal abscess is suspected, ultrasound will aid a veterinarian in diagnosing it, but surgery may be needed to address the abscess.

Sometimes bacterial cultures will be performed to diagnose the specific type of bacteria causing an abscess. This will aid the veterinarian in determining the appropriate antibiotic treatment.

How to Treat Abscesses in Cats

Surgically opening or removing the abscess and maintaining drainage of pus are the primary treatments for most abscesses. Antibiotics are often needed in addition to drainage to clear infection. Tooth extractions may be necessary for tooth root abscesses (along with thorough dental cleaning).

Prognosis for Cats with Abscesses

With prompt, aggressive treatment, abscesses are usually easy to treat and will heal quickly. Infections that have spread to the joints, bone, or bloodstream have a higher risk of long-term damage or fatality, but these cases are rare in well-tended cats.

How to Prevent Abscesses

Keeping cats indoors will help prevent abscesses from fighting wounds. Regular dental cleanings and good oral care will help prevent dental abscesses from forming. Some cats have more problems than others with dental disease, but keeping their teeth clean can help prevent abscesses.