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• Causative agent
• Yersinia pestis (Pasteurella pestis)
• Other names of disease in humans
• black death
• pestis
• both pneumonic and bubonic plague
• Acute, often fatal, potentially epidemic disease

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• Microbiological features of Y. pestis
• gram-negative bacillus
• bipolar staining - characteristic safety pin
• chromosomal and plasmid associated factors
  essential for virulence and survival

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• Epidemiology
• Occurrence
• endemic (urban and rural) in China, India,
  Vietnam, Myanmar, Indonesia, Brazil, Peru, and
  Bolivia
  
• sylvatic (rural) - western US, South America,
  Africa, Asia
  
• 1994 outbreak in Surat, India
• Reservoir
• wild rodents, especially ground squirrels
• lagomorphs
• wild carnivores
• domestic cats

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• Epidemiology
• Mode of transmission
• bite of infected flea, particularly oriental rat
  flea (Xenopsylla cheopis)
  
• human flea (Pulex irritans) in South America
  and other regions abundant on domestic animals
  
• direct contact through handling tissue of
  infected animals
  
• airborne droplets from infected human or animal
  (cats)
  
• laboratory accidents

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• Epidemiology
• Frequency
• worldwide 1,000 cases per year (WHO report)
• in US - 12 cases per year, some acquired from pet
  cats
  
• Epidemics most likely to occur in areas of poor
  sanitation and large rodent populations
  
• Risk in humans is highest during epizootics
  causing high mortality in commensal rats
  
• In US, more likely to occur in summer months

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Prairie dog (Cynomys ludovicianus) - a burrowing
rodent
with a barklike call
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Female oriental rat flea (Xenopsylla cheopis) en
gorged with blood
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• Clinical features
• Incubation period 1-7 days
• Symptoms
• fever, chills, myalgia, prostration, pharyngitis,
  headache
  
• Bubonic form
• lymphadenitis, draining regional lymph nodes
• more commonly in inguinal nodes
• nodes swollen, inflammed, and may be suppurative
• may progress to septicemia (septicemic plague)
• hemorrhage - black spots/bruising of skin -
  called the tokens or Gods marks - hence black
  death

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• Clinical features
• Symptoms
• Septicemic plague
• meningitis
• DIC
• endotoxic shock
• Pneumonic plague
• mediastinitis
• pleural effusion
• pneumonia
• pharyngitis (pharyngeal plague)

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• Clinical features
• Case fatality ratio
• bubonic plague - up to 60 if untreated
• septicemic and pneumonic plague 100if
  untreated
  
• Asymptomatic contacts - organisms can be cultured
  from pharyngeal tissue

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• Clinical features
• Diagnosis
• direct examination of organism from lymph node or
  bubo aspirate, sputum, CSF - suggestive
  
• confirmed by culture and identification or four
  fold rise in titer
  
• PHA - passive hemagglutination using fraction-1
  antigen most frequently used test
  
• FA
• antigen-capture ELISA
• often misdiagnosed

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• Clinical features
• Treatment
• streptomycin - drug of choice
• gentamycin
• TTC
• CHPC
• incision and drainage of suppurative bubos
• Multidrug resistance - mediated by a plasmid,
  hence transferrable reported from patient in
  Madagascar (NEJM, 1997)

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• Prevention/control
• education
• rodent surveillance
• rodent control - especially on ships and
  warehouses
  
• protective gloves for hunting, handling
• maintenance of public sanitation and hygiene
• international travel health awareness