Yersinia pestis

Snapshot

• A 53-year-old man presents to occupational health for suspected exposure to the plague. He works in a research laboratory that conducts research on infectious diseases and accidentally poked himself with a needle he used on an infected animal. He has had headaches, fatigue, and enlarged and painful “bug bite-like lesion” on his right groin.  On physical exam, he has inguinal lymphadenopathy and a large and tender buboe in the right inguinal area. He is started on the appropriate antibiotics, and the incident is reported to the Centers for Disease Control and Prevention.

Introduction

• Classification 
  • Yersinia pestis 
    • a nonmotile, gram-negative, facultative intracellular bacillus
      • non-lactose fermenting, oxidase negative, and does not produce H₂S
    • reservoirs are rats and prairie dogs
    • transmitted via fleas 
    • causes the bubonic plague (most common) and pneumonic plague
• Epidemiology
  • incidence
    • rare but outbreaks occur in the Southwest in the US
  • demographics
    • occurs in young people
  • risk factors
    • exposure with infected patients or small rodents, alive or dead
    • flea bites
    • occupational exposure
• Pathogenesis
  • produces endotoxin, coagulase, and fibrinolysin
  • bacteria migrate to regional lymph nodes and survive intracellularly within macrophages
    • F1 capsular antigen is antiphagocytic 
• Prevention
  • plague vaccine
    • field workers in endemic areas
    • laboratory personnel who work with Yersinia pestis
• Prognosis
  • if untreated, the disease will lead to death
  • if untreated, mortality rates range from 10-50%
• pneumonic plague has the highest mortality

Presentation

• Symptoms
  • sudden onset high fever and chills
  • headache
  • myalgias
  • fatigue
• Physical exam
  • bubonic plague  
    • unilateral swollen and tender lymph nodes (buboes) 
    • often in the groin (Greek bubon = groin) and axilla
    • can grow up to 10 cm in size
    • may have eschar and vesicles
    • buboes may rupture and have malodorous pus discharge
  • pneumonic plague
    • cough
    • chest pain
    • hemoptysis
• dyspnea

Imaging

• Chest radiography
  • indication
    • suspected lung involvement
  • findings
• diffuse patchy infiltrates or consolidations

Studies

• Peripheral blood smear
  • toxic granulations and Dohle bodies
  • Wright-Giemsa stain with rods
  • Wayson stain reveals “safety pin” appearance of bacteria with bipolar staining 
• Labs
  • positive blood cultures are diagnostic but can be hazardous
  • rapid F1 antigen detection via immunofluorescence
• Lymph node aspirate
  • Yersinia pestis on microscopy or culture
• Making the diagnosis
• based on clinical presentation and laboratory studies

Differential

• Anthrax 
  • distinguishing factor
• presents with a necrotic ulcer rather than buboes

Treatment

• Management approach
  • mainstay of treatment is supportive care and antibiotics
• Conservative
  • supportive care
    • indication
      • all patients
    • modalities
      • aggressive hydration
      • respiratory support
      • hemodynamic support
• Medical
  • aminoglycosides
    • indication
      • all patients
  • doxycycline
    • indication
      • treatment
  • fluoroquinolones
    • indication
      • treatment
      • post-exposure prophylaxis
• Operative
  • incision and drainage
    • indication
• enlarging buboes

Complications

• Acute respiratory distress syndrome
• Disseminated intravascular coagulopathy
• Septic shock
• Lymphatic scarring and chronic lymphedema
• Superinfection of buboes with other bacteria