ISSN 2398-2950      

Yersinia pestis


Synonym(s): Y. pestis, plague bacillus




  • 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 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, strict controls enforced by the Center for Disease Control in the United States.
  • Cats 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 cats away from potentially infected rodents.
    Remember - it is zoonotic! Gloves, gowns; isolation of affected animals.
  • Treat fleas on cats.


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


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Pennisi M G, Egberink H, Hartmann K et al (2013) Yersinia pestis infection in cats: ABCD guidelines on prevention and management. J Feline Med Surg 15 (7), 582-584 PubMed.
  • Eidson M, Thilsted J P & Rollag O J (1991) Clinical, clinicopathologic, and pathologic features of plague in cats: 119 cases (1977-1988)​. JAVMA 199 (9), 1191-1197 PubMed.
  • Kaufmann A F, Mann J M, Gardiner T M et al (1981) Public health implications of plague in domestic cats. JAVMA 179 (9), 875-878 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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