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Tularemia

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Reporting Obligations

Confirmed and suspected cases shall be reported to the local Health Unit.

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Epidemiology

Aetiologic Agent

Tularemia (also known as rabbit fever) is a zoonotic bacterial disease caused by the bacterium Francisella tularensis (F. tularensis), which is a highly infectious, small, weakly staining, gram-negative, pleomorphic coccobacillus. May be used as a potential bioterrorism agent.

Clinical Presentation

Clinical presentation is typically sudden, with an abrupt onset of high fever, chills, fatigue, myalgia, nausea and headache. The nature of the illness depends on the site of  inoculation and the virulence of the infecting organism, usually conforming to one of several clinical syndromes, including the following:

  • Ulcero-glandular – cutaneous ulcer with regional lymphadenopathy at the entry site (most common);
  • Glandular – regional lymphadenopathy with no ulcer;
  • Oculoglandular – purulent conjunctivitis and punctate palpebral ulcers, with preauricular lymphadenopathy;
  • Oropharyngeal – stomatitis or pharyngitis (with or without ulcers), or tonsillitis and cervical lymphadenopathy, which may be unilateral;
  • Pneumonic – primary (due to inhalation of the organism) or secondary (due to hematogenous spread of the organism to the lungs) pleuropulmonary disease; and
  • Typhoidal – febrile illness without localizing signs and symptoms

Modes of Transmission

Humans become infected through tick bites, handling infected animal tissues, ingestion of contaminated food or water, and inhalation of contaminated aerosols (such as those generated while sorting contaminated hay or mowing). The average infectious dose for humans is estimated at 10 organisms by subcutaneous inoculation and 25 organisms by aerosol.

Incubation Period

Related to size of innoculum; usually 3–5 days with a range of 1–14 days.

Period of Communicability

Person to person transmission has never been reported; unless treated, infectious agent may be found in blood during first 2 weeks of disease and in lesions for a month; flies infective for 14 days and ticks throughout lifetime (two years); frozen rabbit meat has remained infective for more than three years.

Risk Factors/Susceptibility

All ages are susceptible, and long term immunity follows recovery; re-infection is extremely rare.

  • History of tick or deerfly bite in last 14 days
  • Contact with animals or animal products (i.e. veterinarian, pet industry worker, hunter, trapper, laboratory worker)
  • Consumption of contaminated water
  • Contact with rodents or lagomorphs
  • Consumption of game meat

Diagnosis and Laboratory Testing

Either of the following will constitute a confirmed case of Tularemia:

  • Isolation of Francisella tularensis from an appropriate clinical specimen (e.g., blood, sputum)
  • A significant (i.e., fourfold or greater) rise in serum antibody titre to F. tularensis antigen
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Treatment and Case Management

Treatment is under the direction of the attending health care provider.

Provide education about the illness and how to prevent the spread (avoiding bites of deerflies, mosquitoes and ticks; using insect repellent, wearing light coloured clothing, long sleeved shirts and pants and checking for ticks frequently; cooking game meat thoroughly and using impermeable gloves when dressing game).

Patient Information

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Additional Resources

Ministry of Health and Long-Term Care, “DISEASES: Tularemia.”

References

Ministry of Health and Long-Term Care, Infectious Diseases Protocol, 2019.