Francisella tularensis - Tularemia

  • Diagnosis
  • Background
  • Lab Tests
  • References
  • Related Topics

Indications for Testing

  • A history of contact with rabbits, ticks, dogs, cats, or skunks along with nonspecific febrile illness with prominent lymphadenopathy
    • Negative history of animal contact does not rule out diagnosis

Laboratory Testing

  • Serology – acute and convalescent phase titers
    • Preferred means of confirmation; retrospective in nature
    • Fourfold increase between acute and convalescent serology or >1:160 on acute titer
    • Cross-reactivity between Brucella, Salmonella, Yersinia, and Legionella antigens
  • Culture – frequently negative
    • Difficult to culture – fastidious organism
    • Select agents – confirmed positive culture requires approval before transfer
  • PCR – not widely available but very sensitive
  • Consider testing for other disorders such as Rickettsia rickettsii (Rocky Mountain spotted fever), Rickettsia typhi (typhus fever), Brucella spp, Pasteurella multocida (pasteurellosis)

Imaging Studies

  • Chest x-ray for patients presenting with signs and symptoms of pneumonia – demonstrates infiltrates

Differential Diagnosis

Francisella tularensis is a cause of potentially severe zoonotic disease in humans. It is sometimes referred to as rabbit fever or deer-fly fever.

Epidemiology

  • Incidence – <1/100,000 in U.S.
    • Most cases occur in the west-central and mountain regions – 56% of total cases from 1990-2000 occurred in Arkansas, Oklahoma, Missouri, and South Dakota
  • Transmission – blood-sucking arthropods, contact with infected animals via inapparent abrasions, consumption of contaminated water, airborne spread of contaminated materials
    • Primarily a disease of wild animals, especially rabbits
    • Risk groups – farmers, veterinarians, hunters, landscapers, meat handlers, lab workers
    • In U.S., human vectors are primarily ticks and deer flies
      • Tick vectors include Amblyomma americanum, Dermacentor andersoni, Dermacentor variabilis
    • Peak seasons – spring and summer
      • Historical peaks during fall and early winter (hunting season)

Organism

  • Gram-negative, aerobic, non-spore forming, fastidious coccobacillus
    • Two main biovars are F. tularensis subsp. tularensis (type A) and F. tularensis subsp. holarctica (formerly subsp. palearctica, type B)
      • Type A found predominantly in U.S.
      • Type B found predominantly in Europe and Asia
    • F. tularensis subsp. novicida (type C) – low-virulence strain in North America

Clinical Presentation

  • Average incubation – 3-5 days (range 1-21 days)
  • Disease often begins with the sudden onset of flu-like symptoms, including chills, fever, headache, generalized aches
  • Forms of tularemia (mostly depends on portal of entry)
    • Ulceroglandular
      • Most common form in adults
      • Direct contact with animal or insect bite
      • Starts as small, painful papule that becomes an ulcer at entry portal with associated lymphadenopathy
    • Glandular tularemia – similar presentation to ulceroglandular but lacking ulcer
      • Most common form in children
      • Progresses to fever, chills, myalgia, possibly septicemia
    • Oculoglandular – Parinaud syndrome
      • Conjunctival entry via contaminated fingers, splashes, aerosols
      • Unilateral intense conjunctivitis, preauricular, submandibular, cervical lymphadenopathy
        • Sequelae of corneal perforation and iris prolapse
    • Oropharyngeal and gastrointestinal
      • Ingestion of contaminated food or water
      • Oral – exudative pharyngitis; deep, cervical lymphadenopathy
      • Gastrointestinal – ulcerative GI lesions, diarrhea
    • Pneumonic
      • Inhalational exposure or extension from systemic disease (typically ulceroglandular form)
      • Pneumonia with dry cough, pleuritic chest pain
      • Often occupational exposure (sheep shearing, animal husbandry, farming, lawn/brush cutting, laboratory workers)
    • Typhoidal
      • Rare in U.S.
      • May occur from any portal of entry
        • Usually associated with bacterial gastrointestinal or pneumonic disease and consumption of poorly cooked wild game
      • High fever, headache, diarrhea, sore throat, anorexia
  • Complications – septicemia, meningitis, endocarditis, hepatitis, renal failure
Tests generally appear in the order most useful for common clinical situations. Click on number for test-specific information in the ARUP Laboratory Test Directory.

Francisella tularensis Antibodies, IgG and IgM 2005350
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Limitations 

Cross-reactions with Brucella or Yersinia antibodies may occur; results should be interpreted with caution and correlated with clinical information; the best evidence for current infection is significant change on two appropriately timed specimens

Follow-up 

Convalescent titers 10-14 days may be necessary to confirm disease

General References

Dana AN. Diagnosis and treatment of tick infestation and tick-borne diseases with cutaneous manifestations. Dermatol Ther. 2009; 22(4): 293-326. PubMed

Hepburn MJ, Simpson AJ H. Tularemia: current diagnosis and treatment options. Expert Rev Anti Infect Ther. 2008; 6(2): 231-40. PubMed

Nigrovic LE, Wingerter SL. Tularemia. Infect Dis Clin North Am. 2008; 22(3): 489-504, ix. PubMed

Medical Reviewers

Last Update: August 2016