Introduction

• Bacterial disease in dogs.
• Cause:
  • Infection with Actinomyces spp.
  • Actinomyces is a gram positive filamentous bacteria.
  • Actinomyces can be either facultatively anaerobic or anaerobic.
• Signs: respiratory distress, formation of abscesses in the mouth, lungs or gastrointestinal tract.
• Diagnosis: cytological examination; bacterial culture; histology.
• Treatment: dependent on spp. but often involves prolonged antibiotic use.
• Prognosis: low mortality.
• Actinomycetes are part of the normal bacterial flora of the mucous membranes of mammals.
• They colonize the peridontal mucosal surfaces, and stick to the tooth surfaces to form plaque.
• Endogenous Actinomyces spp cultured from the oral cavities of dogs includes:
  • Actinomyces viscosus Actinomyces viscosus.
  • Actinomyces odontolyticus.
  • Actinomyces bovis.
  • Actinomyces israelii.
  • Actinomyces naeslundii.
• Endogenous Actinomyces spp cultured from the canine vagina includes:
  • Actinomyces colecocanis.
• Normally endogenous Actinomyces spp would not be pathogenic; however, if they enter tissues with other bacteria, infection can result in a pyogranulomatous disease.
• Actinomyces spp associated with Actinomycosis in dogs includes:
  • Actinomyces viscosus Actinomyces viscosus :
    • Causes chronic pneumonia Lung: bacterial pneumonia , pyothorax Pyothorax , and localized subcutaneous abscesses.
  • Actinomyces catuli.
  • Actinomyces turensis.
  • Actinomyces bowdenii.
  • Actinomyces hordeovulneris:
    • Causes localized abscess and systemic infections, eg pleuritis Pleuritis , peritonitis Peritonitis and septic arthritis Arthritis: septic.
  • Arcanobacterium pyogenes (formerlyActinomyces pyogenes Actinomyces pyogenes ).

Pathogenesis

Etiology

• Gram-positive filamentous anaerobic bacteria Actinomyces.
• Actinomycetes are part of the normal bacterial flora of the mucous membranes of mammals.
• Actinomyces spp associated with canine Actinomycosis includes:
  • Actinomyces viscosus.
  • Actinomyces odontolyticus.
  • Actinomyces bovis.
  • Actinomyces israelii.
  • Actinomyces naeslundii.
  • Actinomyces catuli.
  • Actinomyces turensis.
  • Actinomyces bowdenii.
  • Actinomyces hordeovulneris.
  • Actinomyces colecocanis.
  • Arcanobacterium pyogenes(formerlyActinomyces pyogenes).
• Actinomyces spp are opportunistic pathogens. They depend on the disruption of the normal mucosal barriers to cause disease.
• Infection is normally associated with the oropharyngeal area.

Predisposing factors

General

• Opportunistic infections.
• Concurrent disease/mixed bacterial infections.
• Change in bacterial microenvironment.
• Immunosuppression.
• The presence of the tissue-migrating foxtail grass in the environment (Hordeum spp Alopecurus). Muscular movements or air flow causes the grass to burrow through soft tissues.
• Periodontal disease.

Pathophysiology

• Actinomycetes are part of the normal bacterial flora of the mucous membranes of mammals.
• The pathogenesis in dogs usually involves inhalation or ingestion of grass awns (eg foxtail grass) or penetration of skin and soft tissue by a foreign body.
• As infection progresses, granulomas, extensive reactive fibrosis and necrosis, abscesses, draining sinuses, and fistulas develop.
• Actinomycosis spreads by direct extension and is not damaged or diminished in any respect by the normal mucosal barriers.
• Hematogenesis dissemination may occur, but direct spread to adjacent structures is more common.
• The cervicofacial region, thorax, abdomen, retroperitoneal space and subcutaneous tissues are the most commonly affected areas.
• Cervicofacial region:
  • Associated with bite wounds.
  • Perforation of the oropharynx by a foreign body.
  • Chronic gingivitis and or periodonitis.
• Thorax region:
  • Pulmonary infections can develop by aspiration of oropharyngeal material, eg inhalation of grass awn.
  • Pre-existing lung disease may act as a pre-disposing factor for originating infection.
• Abdominal region:
  • Intra-abdominal infections can develop from swallowed organisms or plant material penetrating the gastrointestinal mucosa.
• Retroperitoneal space:
  • Infection of the retroperitoneal space is generally associated with grass foreign bodies. Contaminated grass or awns migrate to the space by migrating through the lung, or by perforating the intestinal wall (eg foxtail grass; see above).
• Bite wounds can cause actinomycosis of the limbs (osteomyelitis Osteomyelitis), this is generally secondary to skin infection.
• CNS infections can develop from hematogenous or lymphatic dissemination from a primary site or direct extension from a simultaneous infection.
• Mixed infections significantly increase the pathogenesis of actinomycosis.
• The bacteria associated with mixed infections tend to be commensal bacteria located either in the oral cavity or intestinal tract. These associated bacteria are able to produce and maintain an anaerobic environment facilitating the proliferation of Actinomyces spp.
• Canine interdigital actinomycosis has also been reported following foreign body penetration, or introduced into a wound by grooming.

Diagnosis

Treatment

Outcomes