Tularemia

Description

• Tularemia is an acute febrile illness caused by the small aerobic gram-negative pleiomorphic intracellular coccobacillus Francisella tularensis:
  • Organism is highly infectious
  • Person-to-person transmission has not been reported
• Humans become infected through different environmental exposures:
  • Bites from infected tick, deer fly, mosquito, or other infected insect
  • Direct contact with infectious animal tissue or fluid
  • Contact with or ingestion of contaminated food, water, or soil
  • Inhalation of infected aerosols (e.g., cutting grass with power mowers, which may aerosolize the organism)
  • Prevention should focus on insect repellents, avoiding untreated surface water, using gloves when handling animals such as rabbits, prairie dogs, rodents, and cooking meat thoroughly
• The 4 major strains of the bacterium have different virulence and geographic location:
  • Two subspecies cause human infection in North America: F. tularensis subspecies tularensis (type A, more virulent) and F. tularensis subspecies holartica (type B, less virulent). In Europe, type B predominates
• Natural hosts:
  • Lagomorphs and other rodents
  • Found in species of wild animals (rabbits, hares, ticks, muskrats, beavers, mice), domestic animals (sheep, cattle, cats), ticks, and water and soil contaminated by infected animals
• Natural vectors:
  • Ticks
  • Biting flies
  • Mosquitoes
  • Wild rabbits
  • Rodents
• Weaponization of tularemia was accomplished during the Cold War:
  • Because of its virulence and ability to be aerosolized, it remains a potential biological agent for mass destruction
• Laboratory technicians handling culture specimens are at high risk:
  • F. tularensis cultures should be manipulated only in a biosafety level 3 facility

Etiology

• Individuals who spend time outdoors in endemic areas are at higher risk:
  • Farmers
  • Hunters
  • Forest workers
  • Lawnmowers/landscapers
  • Those who handle animal carcasses are at highest risk (taxidermists and butchers)
  • Those in contact with polluted waters
  • Two-thirds of cases occur in males
• Although tularemia can occur worldwide, it is endemic in the Northern Hemisphere:
  • Reported nationwide except in Hawaii
  • States with the highest incidence include Missouri, Arkansas, Kansas, South Dakota, and Oklahoma
  • Increased incidence in Colorado, Nebraska, South Dakota, and Wyoming
  • Few hundred cases annually in the U.S., although probably underreported
  • Peak season is June–October
• Mortality is 5–15%. Appropriately treated patients have mortality as low as 1%.

• 25% of cases occur in children 1–14 yr of age
• Children who spend time outdoors in endemic rural areas are at risk