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Corynebacterium pseudotuberculosis


Synonym(s): Corynebacterium pseudotuberculosis biovar equi




  • Gram-positive, facultative, intracellular, anaerobic, pleomorphic rod.
  • The strain isolated in the horse is distinct (biovar equi) from that recorded in other species, such as sheep and goats, and natural transmission between species does not take place.

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Clinical Effects



  • Lives in soil and survives well in dry conditions.


  • Unknown, bu tprobably involves entry of the bacteria into the horse via skin wounds or abrasions.
  • Recent studies have shown an association betweenC. pseudotuberculosisinfection and biting insects such asHaemotobia irritans, Stomoxys calcitrans,andMusca domestica.
  • It then spreads via the lymphatic system.

Pathological effects

  • Within the horse, the bacteria is phagocytosed but is able to survive the host's defense mechanisms and replicate intracellularly. This intracellular existence may be related to the organism having a cell wall that contains lipids and the production of a phospholipase D-protein exotoxin. The latter affects the host's defense systems by inhibiting neutrophil chemotaxis and reducing opsonization of bacteria. The bacterial exotoxin also increases vascular permeability and causes endothelial degradation, thereby increasing the spread of infection locally and along lymphatic tracts, as well as leading to localized edema.
  • Three main clinical presentations including muscle abscesses, especially of the pectoral and/or ventral regions, ulcerative lymphangitis, and less commonly internal abscesses of the thorax and abdomen.

Other Host Effects

  • It is thought that host resistance includes both a humoral and cell-mediated immune response.


Control via animal

  • Purulent material removed from abscesses should be contained and properly disposed of to avoid environmental contamination.
  • Affected animals should be kept off of communal pasture ground until drainage has resolved.

Control via environment

  • Any environment that has housed an affected animal should be thoroughly disinfected.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Rhodes D et al (2015) Minimum inhibitory concentrations of equine Corynebacterium pseudotuberculosis isolates (1996-2012). J Vet Intern Med 29 (1), 327-332 PubMed.
  • Barba M et al (2015) Experimental transmission of Corynebacterium pseudotuberculosis biovar equi in horses by house flies. J Vet Intern Med 29 (2), 636-643 PubMed.
  • Britz E et al (2014) The relationship between Corynebacterium pseudotuberculosis biovar equi phenotype with location and extent of lesions in horses. Vet J 200 (2), 282-286 PubMed
  • Kilcoyne I et al (2014) Frequency of Corynebacterium pseudotuberculosis infection in horses across the United States during a 10-year period. J Am Vet Med Assoc 245 (3), 309-314 PubMed.
  • Nogradi N et al (2012) Musculoskeletal Corynebacterium pseudotuberculosis infection in horses: 35 cases (1999-2009). J Am Vet Med Assoc 241 (6), 771-777 PubMed.
  • Spier S J et al (2012) Survival of Corynebacterium pseudotuberculosis biovar equi in soil. Vet Rec 170, 180 PubMed.
  • Pratt S M et al (2005) Evaluation of clinical characteristics, diagnostic test results, and outcome in horses with internal infection caused by Corynebacterium pseudotuberculosis: 30 cases (1995-2003). J Am Vet Med Assoc 227 (3), 441-448 PubMed.
  • Foley J E et al (2004) Molecular epidemiologic features of Corynebacterium pseudotuberculosis isolated from horses. Am J Vet Res 65 (12), 1734-1737 PubMed.
  • Aleman L et al (1996) Corynebacterium pseudotuberculosis infection in horses: 538 cases (1982-1993). J Am Vet Med Assoc 209 (4), 804-809 PubMed.

Other sources of information

  • Aleman M & Spier S J (2015) Corynebacterium pseudotuberculosis infection. In: Large Animal Internal Medicine. 5th edn. Elsevier, USA. pp 1080-1083.

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