Single-celled actinomycetes are part of the healthy bacterial flora of the oral and nasopharyngeal mucous membranes of many animals, including dogs. These rod-shaped microorganisms exist without oxygen (anaerobic), living in a dog's mouth and nasal passages near the throat — they are "good" or probiotic bacteria that stick to mucosal surfaces and form plaque on the teeth.
However, one of the three genera of actinomycetes — actinomyces — can cause the opportunistic disease actinomycosis in dogs. It is a chronic, suppurative, granulomatous bacterial disease of the cervicofacial, thoracic, or abdominal areas, that can occur when any of these other conditions or predisposing factors exist:
- Cut or wound in the mouth.
- Penetration of the skin by a foreign body.
- Ingestion of a foreign body.
- Poor dental hygiene or chronic periodontal disease.
- Lung cancer.
- Prior surgery.
- Simultaneous ear and eye infection.
- Large-breed hunting dogs are more susceptible.
How three species of actinomyces bacteria cause the disease actinomycosis in dogs.
Three species of the actinomyces bacterium are responsible for the disease actinomycosis in dogs: Actinomyces bovis, Actinomyces viscosus, and Actinomyces hordeovulneris.
Most commonly causing "lumpy jaw" disease in cattle, thus its bovine-derivative name, A. bovis bacteria also can cause lumpy jaw in dogs, which is a localized, chronic, and progressive granulomatous abscess on the mandible, maxillae, or other bony tissues in the head. Whether they are introduced through a cut into soft, underlying tissues or contaminate a wound, the bacteria grow unchecked in the anaerobic environment and permeate adjacent bone. Lumpy jaw is characterized by facial distortion, loose teeth which make chewing nearly impossible, and respiratory difficulty due to a swollen nasal cavity.
Bite wounds and perforation by foreign bodies to the head, neck, thorax, and abdomen invites A. viscosus bacteria into the wound site causing cutaneous actinomycosis in dogs presenting as localized subcutaneous abscesses. The bacterium can also cause pneumonia, infection of the chest cavity (pyothorax), and rarely an inflammatory disease of the central nervous system (pyogranulomatous meningoencephalitis).
A rare cause of canine actinomycosis, the A. hordeovulneris bacterial infection presents with localized abscesses or systemic infections such as peritonitis, septic arthritis, pyogranulomatous pleuritis, or internal abscesses in the lungs, liver, and spleen. Introduction of the bacteria is through inhalation and a predisposing factor is foxtail grass.
Symptoms of actinomycosis or bacterial infection in dogs.
Depending on the site of the infection, symptoms of bacterial infection in your dog will vary. If you see any of the following clinical signs, take your dog to your veterinarian at once:
- Subcutaneous sores or abscesses inside the mouth, on the face, or the neck.
- Signs of oozing or drainage tracts close to the site of the infection.
- Pus drainage that contains blood, plasma, or sulfur-like, soft, gray, or white grains — the actinomyces bacteria produce granules.
- Pain or swelling in the jaw.
- Difficulty breathing.
- Rapid breathing.
- Weight loss.
- Behavioral and consciousness changes.
- Infection of the chest cavity.
Diagnosis and treatment of actinomycosis in dogs.
Diagnosis of actinomycosis in your dog is typically based on presenting symptoms or clinical signs of the infection in its various manifestations, a thorough physical examination, and a review of his medical history.
The drainage or pus from abscesses is particularly revealing of a bacterial infection in its granular texture, thus cytology of pus and pleural fluid serves to confirm the presence of the microorganisms. Definitive diagnosis is based on isolation and identification of one of the three species of the actinomyces bacterium. Therefore, a gram stain, which indicates either gram-positive or gram-negative bacteria, is performed and a bacteriologic culture, both of which are necessary to confirm a diagnosis of actinomycosis.
A successful outcome is more likely with cutaneous infections, which are treated with antimicrobials.
One of the clinical symptoms, pyothorax, an infection in the chest, is frequently seen in the disease. Along with repeated drainage of the chest and antimicrobial therapy, the condition is treated with penicillin, sulfonamides, or cephalosporins which may need to be continued long-term.
In cases of subcutaneous infection, your veterinarian will surgically remove the infected tissue under anesthetic to allow drainage. Infected masses in the abdomen, liver, or spleen will require more invasive surgery. If the infection has reached the bone, surgical options are limited.
Prevention of actinomycosis.
Actinomycosis develops slowly, so if you notice any signs of bacterial infection, take your dog to the vets right away. You can reduce the chances of your dog becoming infected with actinomycosis by avoiding grassy wilderness areas and checking her mouth often for cuts and wounds. Keep in mind that even tiny scrapes and lacerations can become infected. If you find any sores on your dog, either regularly clean and sterilize the wounds yourself, or take her to the vets for treatment. Always seek veterinary treatment immediately if you notice any signs of infection.
Like all illnesses in dogs, early detection, diagnosis, and therefore prompt treatment lead to a more successful outcome for your canine pal.