Francisella

• Francisella

  • Poorly staining Gram-negative, small pleomorphic rods or coccobacilli
  • Non-motile, obligate aerobes
  • A relatively thick capsule can be present (virulent isolates)
  • Oxidase-negative, weakly Catalase-positive, and non-fermentative
  • Grow best on blood agar supplemented with cysteine
• Biotypes of Francisella tularensis

  • Biotype A (tularensis) - northern hemisphere, predominating in North America; associated with terrestrial animal reservoirs, more virulent, referred to as tularensis (formerly subsp. neartica)
  • Biotype B (holartica) - in Eurasia; frequently linked to water-borne infections and to aquatic animals, milder, referred to as holarctica (formerly subsp. palaeartica)
• Reservoir hosts of Francisella tularensis

  • Wild animals such as: rabbits and hares, beavers, muskrats, squirrels, woodchucks, opossums, skunks, deer and foxes
  • Domestic fowl can act as reservoir of infection
• Vectors of Francisella tularensis

  • Dermacentor variabilis
  • D. andersoni
  • Amblyomma americanum
  • Deerfly (Chrysops discalis)
• Francisella

  • Poorly staining Gram-negative, small pleomorphic rods or coccobacilli
  • Non-motile, obligate aerobes
  • A relatively thick capsule can be present (virulent isolates)
  • Oxidase-negative, weakly Catalase-positive, and non-fermentative
  • Grow best on blood agar supplemented with cysteine
• Biotypes of Francisella tularensis

  • Biotype A (tularensis) - northern hemisphere, predominating in North America; associated with terrestrial animal reservoirs, more virulent, referred to as tularensis (formerly subsp. neartica)
  • Biotype B (holartica) - in Eurasia; frequently linked to water-borne infections and to aquatic animals, milder, referred to as holarctica (formerly subsp. palaeartica)
• Reservoir hosts

  • Rabbits and hares
  • Beavers
  • Muskrats
  • Squirrels
  • Woodchucks
  • Opossums
  • Skunks
  • Deer
  • Foxes
  • Domestic fowl
• Vectors

  • Dermacentor variabilis
  • D. andersoni
  • Amblyomma americanum
  • Deerfly (Chrysops discalis)
• Direct Microscopy

  Fluorescent Antibody Test (FAT)
• Glucose-Cysteine blood agar


  1. Incubated aerobically at 37°C for 7 days

  2. Addition of antibiotics such as Penicillin, Polymyxin B sulfate, and cycloheximide when samples are contaminated
• Suitable liquid media

  • Peptone-Cysteine broth
  • Casein hydrolysate
• MacConkey Agar - absence of growth
• Serology

  Slide agglutination test
• Francisella tularensis

  Tularemia/Deerfly Fever/Rabbit Fever/Ohara's Disease
• Hosts

  • Wildlife species (lagomorphs, rodents, coyotes)
  • Domestic animals (sheep, horse, pig, birds)
  • Human
• Transmission

  • Skin abrasions or arthropod bites
  • Inhalation
  • Ingestion
• Symptoms

  • Lymphadenitis, either local or generalized is a constant finding and septicemia is common - fever, depression, inappetence, stiffness
• Postmortem lesions

  • Pale necrotic foci in enlarged superficial LN and miliary lesions may be evident in the liver and spleen, areas of pulmonary consolidation may also be present
• Diagnosis

  Microscopy and Bacterial cultures, isolation must be carried out in a biohazard cabinet
• Treatment and Prevention

  • Antimicrobial therapy (Amikacin, streptomycin, impenem-cilastatin and fluoroquinolones)
  • Ectoparasite control