Felis ISSN 2398-2950

Actinomycosis

Contributor(s): Karen Coyne, Melissa Kennedy

Introduction

  • Bacterial disease.
  • 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.
  • Normal feline Actinomyces spp found in oral cavity:
  • 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 cats includes:

Pathogenesis

Etiology

  • Gram-positive filamentous anaerobic bacteria Actinomyces.
  • Actinomycetes are part of the normal bacterial flora of the mucous membranes of mammals.
  • 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.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Billington S J, Post K W, Jost B H (2002) Isolation of Arcanobacterium (Actinomyces) pyogenes from cases of feline otitis externa and canine cystitis. J Vet Diagn Invest 14 (2), 159-162 PubMed.
  • Pascual C, Foster G, Falsen E et al (1999) Actinomyces bowdenii sp. nov., isolated from canine and feline clinical specimens. Int J Syst Bacteriol 49 (Pt 4), 1873-1877 PubMed.
  • Johnson K A, Lomas G R, Wood A K (1984) Osteomyelitis in dogs and cats caused by anaerobic bacteria. Aust Vet J 61 (2), 57-61 PubMed.
  • Brennan K E, Ihrke P J (1983) Grass awn migration in dogs and cats: A retrospective study of 182 cases. J Am Vet Med Assoc 182 (11)1201-1204 PubMed.

Other sources of information

  • Edwards D F (2006) Actinomyocis and Nocardiosis. In: Infectious Diseases of the Dog and Cat. 2nd Edn. Ed. Greene C E. W B Saunders Co. pp 451-456.


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