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Tularemia (Rabbit Fever)

Tularemia (also known as "rabbit fever" and "deer fly fever") is a disease that was first recognized as a plague-like disease of rodents in 1911 in Tulare, California. It is caused by a highly infectious bacterium that is widespread "in nature," occurring in a variety of wild animals, in water, and even in soil. The bacterium is not dependent on arthropod transmission, but can be transmitted by ticks and deer flies. Around 200 human cases are diagnosed yearly with a fatality rate of 5-7% of untreated patients. Initial symptoms of infection vary depending on the route of inoculation.

Causative agent

  • A bacterium with the scientific name Francisella tularensis.

Geographical distribution of cases

  • Worldwide, but primarily in the northern hemisphere, including Asia and North America.
  • Most cases occur in the south central U.S., especially on the Ozark Plateau of Missouri.

Symptoms of infection

  • General symptoms include fever, headache, chills, nausea, and dry cough.
  • An ulcerated lesion at the site of bacteria inoculation in about 80% of patients, including at a tick bite or, following other contact with F. tularensis, at a cut on a finger or inside the mouth.
  • Can include swollen regional lymph nodes, potentially can develop into pneumonia, and can be fatal.

Reservoir hosts of Francisella tularensis

  • Various wild animals, especially rabbits, hares, and rodents.
  • NOTE: this bacterium also occurs in water and in soil.

Vectors of Francisella tularensis

  • Amblyomma americanum, the lone star tick.
  • NOTE: a species of deer fly is a vector in the western U. S., but transmission by deer flies has not been documented in the eastern U.S.

Modes of transmission

  • Most infections are acquired when hunters handle infected small mammals, especially rabbits.
  • Some infections via ingestion of under cooked meat of infected small mammals, especially rabbits.
  • Some infections via handling infected aquatic mammals such as muskrats.
  • Some infections via ingestion of water that is contaminated with bacteria.
  • Via bites of infected infected ticks in the south central U.S. and deer flies in the western U.S.
  • NOTE: There is no known human-to-human transmission.

Diagnosis of infection

  • A small, ulcerated lesion at the site of bacterial introduction (see "Symptoms of Infection" above).
  • The lesion usually has a pinkish pit in the center and a raised, ridge-like wheal around the perimeter.
  • General symptoms together with a history of activity in habitats in which tularemia occurs.
  • Confirmation is based on laboratory test of blood or bloody sputum.

Treatment of infection

  • Antibiotic prescribed by a physician.

Prevention of infection

  • There is no vaccine for the general public, but one is available for people in high-risk occupations.
  • Avoid tick habitat and contact with infested vegetation (see E-243-W "The Biology and Medical Importance of Ticks in Indiana" (PDF 757KB)).
  • Wear clothing consisting of a long sleeved shirt, long pants, and boots.
  • Use a repellent recommended by CDC and treat clothing with permethrin.
  • Handle game animals such as rabbits with care, especially when skinning and dressing.
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