Canis ISSN: 2398-2942


Contributor(s): Karen Coyne, Melissa Kennedy


  • Bacterial disease in dogs.
  • Cause:
    • Infection withActinomycesspp.
    • Actinomycesis a gram positive filamentous bacteria.
    • Actinomycescan 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.
  • EndogenousActinomycesspp. cultured from the oral cavities of dogs includes:
    • Actinomyces viscosus Actinomyces viscosus.
    • Actinomyces odontolyticus.
    • Actinomyces bovis.
    • Actinomyces israelii.
    • Actinomyces naeslundii.
  • EndogenousActinomycesspp. cultured from the canine vagina includes:
    • Actinomyces colecocanis.
  • Normally endogenous Actinomycesspp. would not be pathogenic; however, if they enter tissues with other bacteria, infection can result in a pyogranulomatous disease.
  • Actinomycesspp. associated with Actinomycosis in dogs includes:



  • Gram-positive filamentous anaerobic bacteriaActinomyces.
  • Actinomycetes are part of the normal bacterial flora of the mucous membranes of mammals.
  • Actinomycesspp. 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).
  • Actinomycesspp. 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

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


  • 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 Actinomycesspp.
  • Canine interdigital actinomycosis has also been reported following foreign body penetration, or introduced into a wound by grooming.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Boothe H W, Howe L M, Boothe D M, Reynolds L A, Carpenter M (2010) Evaluation of outcomes in dogs treated for pyothorax: 46 cases (1983-2001). J Am Vet Med Assoc 236 (6), 657-663 PubMed.
  • Doyle J L, Kuipers von Lande R G, Worth A J (2009) Intra-thoracic pyogranulomatous disease in four working dogs. N Z Vet J 57 (6), 346-351 PubMed.
  • Barnes L D & Grahn B H (2007) Actinomyces endophthalmitis and pneumonia in a dog. Can Vet J 48 (11), 1155-1158 PubMed.
  • Junius G, Bavegems V, Stalpaert M, Binst D, Schrauwen E (2004) Mitral valve endocarditis in a labrador retriever caused by an actinomyces species identified as Actinomyces turicensis. J Vet Intern Med 18 (6), 899-901 PubMed.
  • Davies D R, Lucas J (2003) Actinomyces infection in a dog with pulmonary carcinoma.Aust Vet J 81 (3), 132-135 PubMed.
  • 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.
  • Hoyles L, Falsen E, Foster G, Collins M D (2002) Actinomyces coleocanis sp. nov., from the vagina of a dog. Int J Syst Evol Microbiol 52 (Pt 4), 1201-1203 PubMed.
  • Rooney M B, Monnet E (2002) Medical and surgical treatment of pyothorax in dogs: 26 cases (1991-2001). J Am Vet Med Assoc 221 (1), 86-92 PubMed.
  • Sivacolundhu R K, O'Hara A J, Read R A (2001) Thoracic actinomycosis (arcanobacteriosis) or nocardiosis causing thoracic pyogranuloma formation in three dogs. Aust Vet J 79 (6), 398-402 PubMed.
  • Couto S S, Dickinson P J, Jang S, Munson L (2000) Pyogranulomatous meningoencephalitis due to Actinomyces sp. in a dog. Vet Pathol 37 (6), 650-652 PubMed.
  • Hoyles L, Falsen E, Foster G, Pascual C, Greko C, Collins M D (2000) Actinomyces canis sp. nov., isolated from dogs. Int J Syst Evol Microbiol 50 Pt 4, 1547-1551 PubMed.
  • Pelle G, Makrai L, Fodor L, Dobos-Kovács M (2000) Actinomycosis of dogs caused by Actinomyces hordeovulneris. J Comp Pathol 123 (1), 72-76 PubMed.
  • Pascual C, Foster G, Falsen E, Bergström K, Greko C, Collins M D (1999) Actinomyces bowdenii sp. nov., isolated from canine and feline clinical specimens. Int J Syst Bacteriol 49 Pt 4, 1873-1877 PubMed.
  • Kirpensteijn J, Fingland R B (1992) Cutaneous actinomycosis and nocardiosis in dogs: 48 cases (1980-1990). J Am Vet Med Assoc 201 (6), 917-920 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 182,1201-1204 PubMed.
  • Moens Y, Verstraeten W (1980) Actinomycosis due to Actinomyces viscosus in a young dog. Vet Rec 106 (15), 344-345 PubMed.

Other sources of information

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