Microbiology 2: Yersinia pestis and Plague

General Properties of Yersinia pestis

• Non-motile, non-spore-forming, gram-negative bacillus.
• Exhibits pleomorphism and bipolar staining.
• Member of the Enterobacteriaceae family, alongside other pathogenic Yersinia species like Y. pseudotuberculosis and Y. enterocolitica.
• Contains virulence plasmids responsible for producing the F1 antigen, a glycoprotein capsule, and enzymes with various activities such as phospholipase and protease.

Pathogenesis

• Transmitted via lymphatic system from the site of inoculation to regional lymph nodes.
• Ingestion by phagocytes allows Y. pestis to multiply within immune cells.
• Potential for hematogenous spread leading to hemorrhagic lesions in various organs and tissues.

Disease Cycles

• Two primary cycles: sylvatic (wild) and urban (domestic).
• Maintained by specific rodent reservoirs including:
  • Rock squirrels
  • Ground squirrels
  • Prairie dogs
  • Mice and voles
• Sylvatic plague predominantly affects animal populations and can enter an enzootic state with low rodent mortality and steady disease levels.

Clinical Presentation and Management

• Requires understanding of specimen collection for culture, treatment options, and preventive measures against plague.
• Presence of virulence factors contributes to the severity and spread of the disease.
• Recognition of disease cycles is crucial for control strategies and public health management.