Abscesses in dogs: symptoms, tests and treatment

Overview

A subcutaneous abscess forms beneath the skin, but pus-filled cavities can also develop in deeper tissues. Abscesses are often named after the tissue or organ affected. A tooth root abscess lies around the tip of a tooth root. An anal sac abscess may form when the sac becomes blocked or inflamed. An abscess originating at an upper back tooth root may cause swelling below the eye.

An abscess beneath the skin may feel firm or soft and fluid-filled. A deep abscess may go unnoticed externally because it does not always create an obvious surface lump.

Causes

Bites and other puncture wounds

Another animal's bite carries mouth bacteria beneath the skin. A dog's canine teeth can create a deep cavity below the skin despite a small-looking surface injury. A dog bite can also tear underlying tissues around the puncture opening. A cat bite may leave a deep, narrow puncture that develops bacterial infection. A small puncture opening can close while bacteria remain beneath the skin and infection continues deeper in the tissues. A wood splinter or grass awn can also penetrate skin and cause an abscess.

Infection can also start deeper down

A stick can penetrate the mouth or throat tissues and later cause a neck abscess. Plant material can migrate between tissues away from its original entry point. Several bacterial species may accumulate in the same abscess, including bacteria growing without oxygen. Staphylococci, streptococci and Pasteurella species are among bacteria found in canine skin and subcutaneous abscesses. Common anaerobes cultured from neck abscesses included Bacteroides, Actinomyces and Fusobacterium species.

Risk factors

A deep bite increases abscess risk because teeth carry bacteria into subcutaneous tissues. A thick undercoat may hide a bite injury so that the wound initially goes unnoticed. Chewing or retrieving sticks predisposes dogs to penetrating mouth and throat injuries. Among dogs operated on for neck abscesses, 32.9% had a known history of stick chewing. In that group, no possible cause was known from the histories of 53 dogs.

A previously damaged tooth can be the source of an abscess around its root tip. In an entire male, prostate infection can sometimes lead to a prostatic abscess. A grass awn penetrating between the toes can cause a local subcutaneous abscess.

Typical symptoms

• A lump appears beneath the skin and may enlarge rapidly.
• The swollen area may be tender to touch.
• Skin over the abscess may look red.
• The inflamed wound area may feel warmer than usual.
• A burst abscess may discharge foul-smelling pus.
• Your dog may have a fever even after the abscess bursts through the skin.
• An abscess between the toes may cause constant paw licking.

Of 82 dogs undergoing neck abscess surgery, 97.5% were presented because of visible neck swelling. In the same group, 59.8% had a fever. Loss of appetite occurred in 39%. Difficulty swallowing or chewing was observed in 12.2%. Excessive drooling occurred in 14.6%. Painful swelling or blood-stained discharge beside the anus may be associated with an anal sac abscess.

Complications and consequences

An untreated or inadequately drained abscess can damage surrounding tissue. Pus can drain onto the skin through a tract formed in the tissue, and discharge may continue for a long time. If the causative foreign body remains, an abscess may form again. A deep neck abscess can compress the airway and impair breathing. If an internal organ abscess ruptures inside the body, bacteria may enter the bloodstream.

In a bite injury study, 323 of 1,526 cases were rechecked after treatment (21.2%). Findings consistent with infection were identified in 42 cases at re-examination. Of these, 10 had an abscess (23.8%).

Diagnosis at the vet

Examining the lump and wound

Your vet assesses the lump's location and extent and your dog's general condition. If needed, hair is clipped around the wound to reveal the skin and edges clearly. Examining a very painful or deep bite injury may require sedation. Besides an abscess, neck swelling may result from a tumour or saliva accumulating in tissues. A fine-needle sample can be taken from the lump for microscopic examination of its cells. In the neck abscess study, 39 dogs had a fine-needle sample taken before surgery. If a lesion is near the chest, abdomen or a joint, your vet may also need to assess deeper structures.

Bacterial sampling and imaging

An infected wound can be sampled for bacterial culture and antimicrobial susceptibility testing. With a deep abscess, bacteria growing without oxygen can also be cultured; aerobic culture alone will not find them. In the neck abscess study, samples from 80 dogs were submitted for culture. Cultures were negative in 28.7% of cases. Bacteria grew from 57 dogs' samples. More than one bacterial strain grew in 52.6% of positive cultures.

Conventional X-rays often fail to reveal a grass awn embedded in tissues. Ultrasound may help locate an abscess-associated foreign body. In a small study, ultrasound revealed a finding consistent with a foreign body in 5 of 6 dogs with a longstanding draining tract or abscess. In the neck abscess surgical series, 68 of 82 dogs underwent CT before the procedure. On contrast-enhanced CT, an abscess may appear as a fluid cavity with a rim distinct from its surroundings. An interdigital abscess can resemble interdigital furunculosis, an inflammation originating in hair follicles. One study included 32 dogs with grass awn abscesses and 27 with interdigital furunculosis. A bright linear structure visible in one ultrasound plane was more common in grass awn abscesses. A dark zone surrounding the linear structure also suggested a grass awn.

Treatment

Opening, flushing and drainage

Your vet opens the abscess if needed so that pus can leave the cavity. The cavity is flushed to remove pus and tissue debris. Damaged tissue may need removal. The causative foreign body is removed at the same time where possible. Ultrasound can also guide removal instruments when a foreign body lies deep in soft tissue. Opening and cleaning a painful abscess can be performed under sedation or general anaesthesia. Adequate pain relief is also part of treatment.

A drain may be left in the cavity to carry fluid out of the wound. A passive drain allows fluid to escape by gravity. An active drain removes fluid using suction. A Penrose drain is often removed within 2–4 days once discharge has decreased sufficiently. In the neck abscess surgery study, drains were removed 3–5 days after surgery.

When are antibiotics needed?

A localised subcutaneous abscess can sometimes be treated by opening, draining and local care without antibiotics. Your vet assesses the need for antibiotics according to infection extent and your dog's general condition. An antibiotic may suppress infection even though the pus-filled cavity has not drained. In the neck abscess series, swelling initially resolved with antimicrobials in 9 dogs but returned after treatment ended. In that study, 9 of 57 positive cultures led to an antimicrobial change because of resistance.

Recovery after neck abscess surgery

In a study of 82 dogs undergoing neck abscess surgery, treatment was successful in 92.7%. Recurrence was confirmed or suspected in 6 of 82 dogs (7.3%). Among recurrent cases, the median interval from surgery to returning symptoms was 47 days. Observed recurrences occurred 7–176 days after surgery. Surgical wound healing problems occurred in 9 of 82 dogs (10.9%). Five of 82 dogs needed another procedure to repair the wound because of healing problems. In the same study, 4 dogs underwent further surgery specifically for abscess recurrence. In an earlier follow-up of chronic neck abscesses, recurrence occurred in 8 of the 26 surviving dogs (30.7%).

Prevention

Bite-related abscesses can be prevented by avoiding situations in which dogs fight. After a fight, check your dog for wounds because a dense coat can hide bite marks. After walks through long grass, check the skin and paws for grass seeds. Access to long grass can be restricted for a dog repeatedly exposed to awns. Having a damaged tooth examined matters because a fracture can lead to infection around its root tip. For recurrent anal sac abscesses, your vet may consider surgical sac removal to prevent further episodes.

Important for dog owners

Do not squeeze a lump or try to open it with a needle at home. Prevent licking of a treated wound, for example with a protective collar. If a drain has been placed, monitor its attachment and the amount of discharge. Fluid draining from it should decrease as the wound heals. Keep the surrounding area clean according to your care instructions so that discharge on the skin does not irritate it. Contact your practice promptly if the wound swells again or discharge becomes thick and foul-smelling.

Keep your dog calm during recovery so that running or jumping does not strain the wound. Do not put alcohol or hydrogen peroxide into an open wound, as they can damage healing tissue.

Frequently asked questions

Will an abscess heal if it bursts by itself?

Bursting may reduce pressure as some pus escapes. However, a pus-filled cavity or the causative foreign body may remain in the tissues. Your dog may still have a fever after an abscess bursts, so an opened abscess needs veterinary assessment.

Could a lump beneath the skin be something else?

Visible swelling can arise from different tissues, so a lump is examined before any opening procedure. In the neck, accumulated saliva, lymph node inflammation or a tumour may resemble an abscess. An unclear lump may need sampling or further investigations.

Can antibiotics alone treat an abscess?

An antibiotic does not necessarily drain pus from the tissues. Your vet may need to open and flush the abscess to remove its contents. A small subcutaneous abscess can sometimes be treated without antibiotics when drainage and local care are sufficient.

Why have a small bite mark examined?

A small hole left by a dog's tooth can conceal a cavity extending deep beneath the skin. Bacteria may remain below the surface if the puncture opening closes. Your vet assesses the injury's depth and whether flushing or a drainage route is needed.

When should my dog return after an abscess is opened?

Contact your vet if a lump forms again where the abscess was drained or pain increases. Thick, foul-smelling or increasing discharge also warrants reassessment of healing. If breathing becomes difficult or your dog collapses, seek emergency care immediately.