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Bacterial Infection (Actinomycosis) in Dogs

Actinomycosis in Dogs

Actinomycosis stems from an infectious agent represented by gram-positive, branching, and pleomorphic bacteria, primarily of the genus Actinomyces, notably the A. viscosus species. These bacteria possess a unique ability to adapt to low oxygen conditions, ranging from microaerophilic to anaerobic environments. Actinomyces seldom act alone in causing lesions, often participating in polymicrobial infections alongside various bacteria. In fact, Actinomyces may even engage in synergistic interactions with other microorganisms.

Symptoms and Types

  • Pain and fever
  • Infections typically localized on the face or neck area, but may extend
  • Skin swellings or abscesses accompanied by draining tracts; sometimes containing yellow granules
  • Inflammation of the tissue behind the peritoneum, the smooth membrane lining the abdomen (retroperitonitis)
  • Inflammation of bones or vertebrae (osteomyelitis), particularly affecting long bones like those in the limbs; usually secondary to skin infection
  • When associated with spinal cord compression, motor and sensory deficits (e.g., difficulty walking, touching, etc.)


Actinomycosis is believed to arise as an opportunistic infection. For instance, Actinomyces spp. commonly inhabit the mouth of dogs. However, cuts, scrapes, or bite wounds in the mucosa or skin can disrupt the balance in the bacterial microenvironment, leading to infection. Other risk factors include periodontal disease and immunosuppressive disorders.


To diagnose actinomycosis in your dog, provide a detailed history of your pet’s health, including the onset and characteristics of symptoms, to the veterinarian. The vet will conduct a thorough physical examination along with various tests including a biochemistry profile, urinalysis, complete blood count, and electrolyte panel. X-rays of affected dogs typically reveal periosteal new bone formation, reactive osteosclerosis, and osteolysis.

For a more conclusive diagnosis, your veterinarian may collect a sample of pus or osteolytic bone fragments for culturing. Additionally, Gram staining, cytology, and acid-fast staining may be utilized.


The dog’s abscesses will be drained and irrigated for several days. In certain instances, a penrose drain may be inserted, which involves placing a soft rubber tube in the affected area to prevent fluid accumulation. Depending on the seriousness of the infection, your veterinarian may also perform debridement (removal of damaged tissue) or bone removal, necessitating surgery.

Many veterinarians recommend administering antibiotics for at least three to four months after the disappearance of all symptoms. This helps combat other frequently associated microbes.

Living and Management

Monitor the affected area for indications of infection and promptly notify a veterinarian if you observe itching, swelling, redness, and/or drainage. Otherwise, your veterinarian will arrange regular follow-up appointments to closely observe your pet for any recurrence. It’s anticipated that approximately half of the cases will experience a recurrence of infection at the original site.

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