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Rhodococcus equi


Synonym(s): Prescottella equi




  • Order: Actinomycetales.
  • GenusRhodococcus (previously Corynebacterium, now Prescottella).
  • Speciesequi.


  • Greek: rhodos - rose; kokkos - grain, berry, seed.

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Clinical Effects



  • Soil, especially contaminated with feces.
  • In high levels in dust around stables and exercise areas.
  • Has been isolated from gastrointestinal tract of herbivores.


  • Inhalation.
  • Ingestion.
  • In utero (umbilical or mucous membrane exposure).

Pathological effects

  • Polysaccharide capsule allows R. equi  to survive in phagocytes.
  • Virulence conferred by VaPA plasmid.
  • Humoral and cell-mediated responses to infection are shown.
  • Maternally derived antibodies are passed in colostrum and milk, but decline by 6-12 weeks of age.
  • Most cases occur at an age when maternal antibody levels wane (1-4 months of age). Infection likely occurs in the fist 2 weeks of life, but clinical signs do not develop until the foal is slightly older.
  • Immaturity of local immune defenses in respiratory tract of foal may play a role in their increased susceptibility to disease.
  • Immunosuppression, and debilitation associated with parasitism may predispose to disease.
  • R. equi causes a severe and fulminating bronchopneumonia with pyogranulomatous abscesses, mainly in young foals Rhodococcus equi infection.
  • R. equi is a facultative intracellular bacterium → survives in alveolar macrophages → stimulates pyogranulomatous response in lungs and hilar lymph nodes.
  • Survival in macrophages via inhibition of phagosome-lyosome fusion. R. equi-specific antibodies enhance the fusion process → increased killing ability of macrophages.
  • Organism may also localize in joints, bones, skin Skin: bacterial disease - overview, intestines, mesenteric lymph nodes, or spleen.
  • Uterine infection has been reported.
  • Has been reported as a cause of pneumonia in immunosuppressed human beings.

Other Host Effects

  • May inhabit intestinal tract, particularly of young foals. Possible normal commensal of gastrointestinal (GI) tract; can be cultured from feces of healthy adult horses.
  • Many immunocompetent foals will develop subclinical infection and become immune.
  • Disease prevalence related to amount of exposure. Exposure greater in areas where horses have been present for long periods, where there is a high stocking density, and during warmer months and on dry, windy days.


Control via animal

  • Prompt treatment of cases to prevent outbreaks.
  • Decrease sticking density.
  • Ensure adequate transfer of passive immunity shortly after foaling.
  • Avoid spreading manure on pastures.

Control via chemotherapies

A macrolide (erythromycin, clarithromycin, azithromycin) with rifampicin is the combination of choice.

Resistant organisms have been detected. Therefore antimicrobial sensitivity tests should be carried out.

Control via environment

  • Disinfection of stables.
  • Remove feces from paddocks and stables.
  • Good ventilation and avoidance of dust in stables and yards.


  • Vaccination with a bacterin has been attempted, but does not confer adequate resistance.
  • There is ongoing research investigating other vaccination options.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Giles C et al (2014) Rhodococcus equi (Prescottella equi) vaccines: the future of vaccine development. Equine Vet J 47 (5), 510-518 PubMed.
  • Kilcoyne I, Nieto J & Vaughan B (2014) Tibial osteomyelitis caused by Rhodococcus equi in a mature horse. Equine Vet Educ 26 (6), 283-286 VetMedResource.
  • Boyen F, Pasmans F & Haesebrouck F (2011) Acquired antimicrobial resistance in equine Rhodococcus equi isolatesVet Rec 168 (4), 101 PubMed
  • Giguere S et al (2011) Diagnosis, treatment, control and prevention of infections caused by Rhodococcus equiJ Vet Intern Med 25 (6), 1209-1220 PubMed.
  • Giguere S et al (2011) Rhodococcus equi: Clinical manifestations, virulence and immunity. J Vet Intern Med 25 (6), 1221-1230 PubMed.
  • Reuss S M, Chaffin M K & Cohen N D (2009) Extrapulmonary disorders associated with Rhodococcus equi inection in foals: 150 cases (1987). JAVMA 253 (7), 855-863 PubMed.
  • Davis E (2008) Rhodococcus equi in adult horses. Equine Vet Educ 20 (2), 72-73.
  • Waldridge B M, Morresey P R, Loynachan A T et al (2008) Rhodococcus equi pneumonia in an adult horse. Equine Vet Educ 20 (2), 67-71.
  • Pusterla N, Wilson W D, Mapes S & Leutenegger C M (2007) Diagnostic evaluation of real-time PCR in the detection of Rhodococcus equi in feces and nasopharyngeal swabs from foals with pneumonia. Vet Rec 161 (8), 272-275 PubMed.
  • Davis E (2007) Rhodococcus equi: advanced diagnostics may be indicated when dealing with complicated disease. Equine Vet Educ 19 (5), 237-238.
  • Muscatello G, Gerbaud S et al (2006) Comparison of concentrations of Rhodococcus equi and virulent R. equi in air of stables and paddocks on horse breeding farms in a temperate climate. Equine Vet J 38 (3), 263-265 PubMed.
  • Janicek J C et al (2006) Intracranial abscess caused by Rhodococcus equi infection in a foal. JAVMA 228 (2), 251-253 PubMed.
  • Anzai T et al (1997) Comparison of tracheal aspiration with other tests for diagnosis of Rhodococcus equi pneumonia in foals. Vet Microbiol 56 (3-4), 335-345 PubMed.
  • Hondalus M K (1997) Pathogenesis and virulence of Rhodococcus equiVet Microbiol 56 (3-4), 257-268 PubMed.
  • Prescott J F & Hoffman A M (1993) Rhodococcus equiVet Clin North Am Equine Pract (2), 375-384 PubMed.
  • Leadon D P (1989) Bacteriology and pathogenesis of Rhodococcus equiEquine Vet Educ (1), 25-26.

Other sources of information

  • Chaffin M K (1999) Rhodococcus equi pneumonia in foals - Clinical presentations, treatment and prevention. In: Proc North Am Vet Conference. pp 79-80.

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