Tularemia

Tularemia Basics - Rabbit Fever Rundown

• Causative Agent: Francisella tularensis
  • Gram-negative coccobacillus
  • Strictly aerobic
  • Facultative intracellular pathogen
  • Non-motile, non-spore-forming
  • Requires cysteine for growth (e.g., Buffered Charcoal Yeast Extract agar - BCYE)
• Common Names: Rabbit fever, Deer-fly fever, Ohara's disease.
• Transmission:
  • Arthropod vectors (ticks like Dermacentor, Amblyomma; deer flies like Chrysops)
  • Contact with infected animal tissues (especially rabbits, hares, rodents)
  • Ingestion of contaminated food/water
  • Inhalation of infectious aerosols
• Key Feature: Extremely low infective dose (as few as 10-50 organisms can cause disease).
• Reservoirs: Rabbits, hares, rodents, ticks.

⭐ Francisella tularensis is a Category A bioterrorism agent due to its high infectivity, ease of aerosol dissemination, and ability to cause severe illness and mortality.

Transmission & Forms - How It Spreads & Shows

• Reservoirs: Rabbits, hares, rodents (muskrats, beavers), ticks.
• Vectors: Ticks (Dermacentor, Amblyomma), deer flies (Chrysops).
• Transmission Routes:
  • Arthropod bites (most common)
  • Handling infected animal tissues
  • Ingestion (contaminated food/water)
  • Inhalation of aerosols (F. tularensis - bioterrorism)
  • Direct contact (skin/mucous membranes)

Clinical Forms:

Diagnosis & Management - Spotting & Stopping It

• Diagnosis:
  • Culture: F. tularensis on cysteine media (BCYE, choc agar). BSL-3 lab.
  • Serology: Agglutination ≥1:160, ELISA. Paired sera (4-fold rise).
  • PCR: Rapid, specific. Early diagnosis from samples.
• Management:
  • Drug of Choice (DOC): Streptomycin 1g IM BID or Gentamicin 5mg/kg/d for 10-14 days.
  • Alternatives: Doxycycline 100mg BID or Ciprofloxacin 500-750mg BID for 14-21 days (mass casualty/mild).
  • Post-Exposure Prophylaxis (PEP): Doxycycline or Ciprofloxacin for 14 days.

⭐ F. tularensis: Category A agent. Highly infectious (ID50: 10-50 organisms via aerosol); high morbidity.

Bioterrorism Threat - Weaponized Worry

• CDC Category A: highest priority bioterror agent.
• Highly infectious: low ID₅₀ (10-50 organisms); easily aerosolized.
• Causes severe morbidity; high panic potential.
• Weaponizable due to environmental persistence.

⭐ F. tularensis can remain viable for weeks in diverse environments (water, soil, carcasses), enhancing its weaponization potential.

High‑Yield Points - ⚡ Biggest Takeaways

• Agent: Francisella tularensis, a highly infectious Gram-negative coccobacillus.
• Transmission: Primarily via ticks, deer flies, and contact with infected rabbits/rodents.
• Ulceroglandular: Most common form; skin ulcer with painful lymphadenopathy.
• Pneumonic Tularemia: Key bioterrorism concern; high mortality, aerosol transmission.
• Diagnosis: Serology is mainstay; culture requires special cysteine-enriched media.
• Treatment: Streptomycin or gentamicin are drugs of choice.
• Low Infective Dose: As few as 10-50 organisms can cause infection_._