ISSN 2398-2942      

Yersinia pestis


Synonym(s): Yersinia pestis




  • Family: Enterobacteriaceae.
  • Genus: Yersinia.
  • Species: pestis.


  • Yersin - Swiss-born French bacteriologist.
  • L: pestis - plague or contagious disease.

Active Forms

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Clinical Effects



  • Reservoir: tolerant rodents in endemic areas.


  • By infected fleas: inhabits proximal digestive tract of flea and proliferates until blocks proventriculus.
  • By ingestion of infected rodents.
  • Rarely, by inhalation of sputum from pneumonic plague case.

Pathological effects

  • Specific resistance involves both humoral and cell-mediated responses.
  • Outer membrane proteins (Fraction 1) stimulate opsonin formation.
  • Activated macrophages destroy intracellular organisms.
  • Strong but temporary immunity follows recovery.
  • Antiphagocytic virulence factors (plasmid-encoded V and W factors) lead to bacteremia.
  • Fraction 1 induces high antibody titers.
  • Cats more susceptible than dogs. Dogs develop only mild clinical signs including fever and enlarged lymph nodes.
  • Cats/dogs infected when bitten by infected fleas or ingesting infected rodents.
  • Incubation period 1-2 days.
  • After ingestion, bacteria replicate in oral cavity → spread to tonsils and regional lymph nodes → bacteremia → localization in lungs, liver and spleen in necrotic foci containing bacterial colonies.
  • Virulence factors:
    • Antiphagocytic outer membrane proteins (Fraction 1 and plasmid-encoded V and W factors).
    • Plasmid-encoded exotoxin.
    • Endotoxin (lipopolysaccharide).
    • Plasmid-encoded bacteriocin, coagulase and fibrinolysin.
    • Purine synthesis.
  • Bubonic form: suppurative lymphadenitis.
  • Pneumonic form (20% of cases).
  • Both forms may coexist in same cat.
  • Usually acute form terminating in death in 4-6 days if untreated.
  • Occasional chronic form.

Other Host Effects

  • Reservoir hosts (maintenance or enzootic hosts): tolerant rodents, eg mice, chipmunks, gerbils, and prairie dogs.


Control via animal

  • If plague suspected in cats/dogs, strict controls enforced by the Center for Disease Control in the United States.
  • Cats/dogs should be isolated, handled wearing protective clothing and treated for fleas.
    Plague in cats may be an important source of infection for humans.

Control via chemotherapies

  • Streptomycin Streptomycin.
  • Chloramphenicol Chloramphenicol.
  • Tetracycline Tetracycline - primarily for bubonic form.
  • Treat for a minimum of 21 days.
    Do not wait for confirmation before starting antimicrobial therapy.

Control via environment

  • Keep pets away from potentially infected rodents.
    Remember - it is zoonotic! Gloves, gowns; isolation of affected animals.
  • Treat fleas on pets.


  • None available.
  • Transient protection of humans can be obtained using bacterins.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Runfola J K, House J, Miller L et al (2015) Outbreak of Human Pneumonic Plague with Dog-to-Human and Possible Human-to-Human Transmission-Colorado, June-July 2014. MMWR Morb Mortal Wkly Rep 2015 64 (16), 429-434 PubMed.
  • Nichols M C, Ettestad P J, Vinhatton E S et al (2014) Yersinia pestis infection in dogs: 62 cases (2003-2011). JAVMA 244 (10), 1176-1180 PubMed.
  • Wang H, Cui Y, Wang Z et al (2011) A dog-associated primary pneumonic plague in Qinghai Province, China. Clin Infect Dis 52 (2), 185-190 PubMed.
  • Gould L H, Pape J, Ettestad P et al (2008) Dog-associated risk factors for human plague. Zoonoses Public Health 55 (8-10), 448-454 PubMed.

Other sources of information

  • Macy D (2006) Plague. In: Infectious diseases of the Dog and Cat. Greene C (ed). 3rd edn. Elsevier, Inc.

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