Equis ISSN 2398-2977

Streptococcus spp

Contributor(s): Sarah Binns, Susan Dawson, Richard Walker




  • Family: Streptococceae.
  • Genus:Streptococcus.


  • Gk: streptos - twisted;Gk: kokkos - grain, berry, seed.

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Clinical Effects



  • Many commensals on mucosal surfaces of respiratory and urogenital systems in healthy horses.


  • Streptococci are resident on the mucous membranes of the upper respiratory tract, lower genital and alimentary tract.
  • Reproduction is by binary fission to form chains or pairs.


  • Many infections stress-related from commensals.
  • Inhalation, ingestion, congenital, sexual or indirect transmission via feed, water or fomites.

Pathological effects

  • Capsules of some species antiphagocytic.
  • Purpura hemorrhagica may follow strangles   Strangles (Streptococcus equi infection)  and may be mediated by immune complexes.
  • Immune-complex glomerulonephritis reported followingS. equi zooepidemicussubspecies infection.
  • Host defense mainly relies on phagocytosis.
  • Antibodies may be raised against M protein.
  • Recovered animals are temporarily immune to reinfection.
  • Immunity is serotype-specific.
  • Pyogenic bacteria often cause abscess formation and suppuration.
  • Beta-hemolytic isolates mostly pathogenic.
  • Exotoxins produced - streptolysin O and S, hyaluronidase, DNase, protease and streptokinase.
  • Adhesins mediate attachment.
  • Trigger inflammation and suppuration.
  • Strangles, or contagious rhinopharyngitis   Strangles (Streptococcus equi infection)  , is caused byStreptococcus equisubspeciesequi.
  • Equine metritis   Uterus: contagious equine metritis  , neonatal infections, and secondary pneumonia caused byS. equisubspecieszooepidemicus.

Other Host Effects

  • Many are commensals on mucosal surfaces of upper respiratory and urogenital tracts.


Control via animal

  • Isolate suspected cases of strangles.
  • Treat adequately to avoid systemic spread.
  • Hygiene.

Control via chemotherapies

  • Pathogenic streptococci are usually susceptible to penicillin, chloramphenicol, cefalosporins, and potentiated sulfonamides.
  • Streptococci are often resistant to aminoglycosides and tetracyclines.

Control via environment

  • Hygiene.
  • Isolate affected animals.



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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Wilsher S & Allen W R (2006) Effects of a Streptococcus equi infection-mediated nutritional insult during mid-gestation in primiparous Thoroughbred fillies. Part 1: Placental and fetal development. Equine Vet J 38 (6), 549-557 PubMed.
  • Jacobs A A C et al (2000) Investigations towards an efficacious and safe strangles vaccine; submucosal vaccination with a live attenuated Streptococcus equi. Vet Rec 147, 563-567 PubMed.
  • Wood J L N, Burrell M H, Roberts C A, Chanter N & Shaw Y (1993) Streptococci and Pasteurella spp associated with disease of the equine lower respiratory tract. Equine Vet J 25 (4), 314-318 PubMed.

Other sources of information

  • Horserace Betting Levy Board (2016) Codes of Practice. 5th Floor, 21 Bloomsbury Street, London WC1B 3HF, UK. Tel: +44 (0)207 333 0043; Fax: +44 (0)207 333 0041; Email: enquiries@hblb.org.uk; Website: http://codes.hblb.org.uk.
  • Biberstein E L (1999) Streptococci. In: Veterinary Microbiology. Eds: D C Hirsh & Y C Zee. Blackwell Scientific, USA. pp 157-164. ISBN: 0 86542 085 8.