Actinomycosis in Dogs

Summary

Actinomycosis is a type of bacterial infection caused by a variety of Actinomyces species bacteria. Many cases of actinomycosis present as infected wounds or abscesses. These abscesses are commonly found around the face and neck, but they may appear anywhere a penetrating injury has occurred.  Actinomyces bacteria are commonly found in the mouth and are harmless unless they are introduced into deeper tissues through an open cut or puncture wound. A break in the skin caused by an object like a stick, thorn, or grass awn that’s contaminated with these bacteria, can lead to a deep abscess or infection. These bacteria cannot penetrate healthy skin on their own, but once they’re pushed into deeper tissues as the result of an injury, they can set up housekeeping and cause a severe infection. The only way to determine if your dog’s abscess or infection is specifically actinomycosis is to have your vet take a sample from the infected tissue to analyze what kind of bacteria are present in the infection. This type of diagnostic test usually isn’t necessary because most abscesses and infections heal quickly with a generalized approach to therapy.

Risk Factors

Actinomycosis is rarely diagnosed in dogs. Most pet owners do not have to worry about it. Although it is uncommon, dogs who are more likely to 

• Get in a fight

• Receive a puncture wound

• Receive a bite wound

are the most at-risk of developing this type of infection. Although this condition is rare, hunting dogs as a group are more likely to develop actinomycosis than dogs who do not perform this type of work.

Possible Causes

Actinomycosis can only be caused by a puncture wound that has been contaminated with this bacteria. The contamination can originate from inside the infected dog’s own mouth or it may have been transmitted by whatever object or animal caused the wound. The presence of these bacteria in the mouth don't cause disease or infection on their own. They live benignly in the mouth along the gum line and only pose a risk when they are introduced to an open wound.

Main Symptoms

Abscesses, Infected or Draining Wounds (especially around face and neck)

Other Possible Symptoms

Actinomycosis generally presents as abscesses or sores in or under the skin. Other indications include:

• Hard, solid lumps in the skin

• Open and draining lumps on the skin surface

• A small hole in the skin that doesn’t heal and drains fluid

• Loss of appetite

• Weight loss

• Fever

• Lethargy 

If left untreated or undetected, more serious cases can develop. It's important to note that the original wound in the skin may have been tiny, albeit deep, and might have healed completely before the dog starts displaying symptoms of internal illness.

The types of infections that result from actinomycosis vary widely. The severity of the infection itself can range from mild to severe, and the impact of the infection will vary depending on its location.  When a wound is small and the infection is not spreading, a dog with actinomycosis isn’t likely to develop serious secondary symptoms.  Instead, the wound won’t heal quickly and will show signs of infection like redness, swelling, and drainage. If the wound is larger and the infection spreads throughout the body, the dog will show generalized signs of illness like fever, lethargy, and appetite loss.

If the wound is confined to a small area just under the skin, it's much less likely to cause severe signs of illness. If the initial wound is deep and enters the chest cavity, the subsequent infection in the space around the dog’s heart and lungs can be life threatening. If the wound punctures the abdominal cavity, the dog may develop symptoms like a swollen, painful belly, or you may even be able to feel a hard mass inside.  Infected wounds on the extremities can lead to limb swelling and lameness.  If the site of infection is near nerves, weakness and paralysis can result.

Testing and Diagnosis

Veterinarians generally do not need to take the time to diagnose actinomycosis specifically, since generalized treatment strategies for infections are usually effective. Your vet will decide how aggressively to pursue a diagnosis based on the severity of your dog's symptoms and his response to therapy. Diagnostic tests may include, but are not limited to:

• Blood tests

• X-rays

• Fluid analysis

• Ultrasound

Steps to Recovery

Any signs of infection should be investigated and diagnosed by a veterinarian. If left untreated, actinomycosis may become life-threatening. A dog’s condition can deteriorate relatively quickly depending on the location of the infection. 

Surgical intervention and medication are usually both necessary to treat actinomycosis. The dog is placed on an appropriate antibiotic, and surgery is performed to remove masses, drain abscesses, or cut away infected tissue. A long course of antibiotics is usually required to effectively resolve actinomycosis. Treatment may be required for weeks or even months after visible signs of infection have improved. With aggressive treatment, cure rates of up to 90% have been reported. Relapse is common, with up to 40% of dogs experiencing a recurrence.

Prevention

Actinomycosis is only transmitted when wounds are contaminated with Actinomyces bacteria.  These bacteria are normally present in the mouths of healthy animals without causing disease.  Infection only occurs when the skin (or similar surface like the lining inside the mouth) is broken.  As such, this is a perfect example of a disease that is infectious in nature, but not contagious.   Actinomycosis does not spread from pet to pet or from pet to person without being introduced to deeper tissues because of a wound.

How Common is Actinomycosis in Dogs?

Actinomycosis is a rare disease.  Although many pet parents will have to deal with a skin infection at some time during their pet’s life, these occurrences are unlikely to be related to actinomycosis.

Typical Treatment

Antibiotics, surgery