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