Tularemia

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Basics

Zoonotic infection caused by two subspecies of the bacterium Francisella (Francisella tularensis [70% of cases in North America] and Francisella holarctica)

Description

  • Life-cycle components
    • Gram-negative coccobacillus
    • Mammalian reservoirs: lagomorphs (hares, rabbits, and pikas), free-roaming cats, and rodents
    • Vectors: ticks, flies, and mosquitoes
  • Incubation ranges from 1 to 21 days (average is 3 to 4 days). Clinical disease has ulceroglandular, glandular, typhoidal, oculoglandular, pneumonic, or oropharyngeal manifestations.
  • System(s) affected: cardiovascular, hematologic/lymphatic/immunologic, pulmonary, skin/exocrine, neurologic
  • Synonym(s): rabbit fever; deer-fly fever; Pasteurella tularensis; Bacterium tularense; tick fever; Ohara disease; Francis disease

Epidemiology

Incidence
  • 11% increase over prior 10-year average of U.S. cases reported in 2015
  • Average of 158 cases per year in United States from 2005 to 2015
  • 2013 CDC 314 U.S. cases: 53% in Colorado, Kansas, Missouri, Nebraska, and South Dakota
    • Predominant age (bimodal): 5 to 9 years and 40 to 64 years; predominant sex: males
    • Seasonal: usually summer, 50% of cases, especially in children

Etiology and Pathophysiology

  • F. tularensis is highly infectious; can enter via skin, mouth, eyes, throat, or respiratory tract
  • Most commonly acquired via tick (in U.S. dog tick, wood tick, and lone star tick), deer fly (Chrysops; less common than tick), or mosquito (especially in Eastern Europe) bite
  • Tick and deer fly bites usually result in glandular or ulceroglandular tularemia.
  • Aerosol inhalation from contaminated dust, hay, or animal pelts
  • Contact of skin or mucous membranes with blood or tissue of infected carcass (F. tularensis can penetrate unbroken skin.)
  • Ingestion of undercooked meat of infected animals or consumption of contaminated water
  • Laboratory-acquired infections (usually respiratory)
  • Respiratory infection most likely if biologic terrorism
  • No documented person-to-person spread
  • Francisella survives for months in a moist natural environment.
  • F. tularensis is more virulent than F. holartica.

Risk Factors

  • Location: endemic in U.S. Midwest
  • Non–U.S. cases occur in Eastern Europe, China, Japan, and rural areas of Northern Europe.
  • Outdoor work; handling wild game or infected hay
  • Pet owners: domestic and exotic
  • Laboratory work with Francisella organisms

General Prevention

  • Wear tick/mosquito repellents with DEET; avoid squeezing body of attached tick.
  • Particular caution handling rabbits and rodents
  • Avoid contact with high-risk animal carcasses or with material (e.g., water) that may have been in contact with infected animals.
  • Cook wild game thoroughly.
  • Lab workers: Wear protective hoods and use negative-pressure cabinets when working with F. tularensis:
    • Follow biosafety level 3 precautions.
  • Intradermal, live attenuated, unlicensed vaccine is available for high-risk persons (laboratory personnel or high-risk military).

Commonly Associated Conditions

  • Other arthropod-borne diseases
  • Tularemic conjunctivitis
  • Bacteremia/septicemia/pneumonia
  • Lymphadenopathy

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