Tularemia

Key Features

Essentials of Diagnosis

• History of outdoor activity

• Possible contact with rabbits, other rodents, and biting arthropods (eg, ticks in summer) in endemic area

• Fever, headache, nausea, and prostration

• Papule progressing to ulcer at site of inoculation

• Enlarged regional lymph nodes

• Serologic tests or culture of ulcer, lymph node aspirate, or blood confirm the diagnosis

General Considerations

• An infection of wild rodents—particularly rabbits and muskrats—with Francisella (Pasteurella) tularensis

• Usually acquired by contact with animal tissues (eg, trapping muskrats, skinning rabbits), from ticks, or from biting flies

• Risk factors for pneumonic tularemia include lawn-mowing and brush-cutting, underscoring the potential for probable aerosol transmission of the organism

• The incubation period is 2–10 days

• F tularensis has been classified as a high-priority agent for potential bioterrorism use because of its virulence and relative ease of dissemination

Clinical Findings

Symptoms and Signs

• Papule

  • Develops at inoculation site and soon ulcerates

  • May be on the skin of an extremity or in the eye

• Widespread organ involvement may occur but may be entirely asymptomatic

• Fever, headache, and nausea begin suddenly

• Regional lymph nodes

  • May become enlarged and tender

  • May suppurate

• Pneumonia

  • May develop from hematogenous spread of the organism or

  • May be primary after inhalation of infected aerosols, which are responsible for human-to-human transmission

• Following ingestion of infected meat or water, an enteric form may be manifested by

  • Gastrointestinal symptoms

  • Stupor

  • Delirium

• In any type of involvement, the spleen may be enlarged and tender and there may be nonspecific rashes, myalgias, and prostration

Differential Diagnosis

• Anthrax

• Cat-scratch disease

• Infectious mononucleosis

• Plague

• Typhoid fever

• Lymphoma

• Rickettsial disease, eg, epidemic typhus, Q fever

• Rat-bite fever

• Meningococcemia

• Sporotrichosis

• Herpes simplex virus conjunctivitis

Diagnosis

Laboratory Tests

• Culturing the organism from blood or infected tissue requires special media. For this reason and because cultures of F tularensis may be hazardous to laboratory personnel, the diagnosis is usually made serologically

• A positive agglutination test (> 1:80) develops within 2 weeks and may persist for several years

• Culture of ulcer, lymph node aspirate, or blood confirms the diagnosis

Treatment

Medications

• Streptomycin

  • Dosage: 7.5–10.0 mg/kg every 12 hours intramuscularly or intravenously for 10 days

  • Drug of choice

• Gentamicin

  • Dosage: 5 mg/kg once daily intramuscularly or intravenously for 10 days

  • Generally less toxic than streptomycin

  • However, some case series report lower treatment success rates

• Doxycycline

  • Dosage: 200 mg/day orally

  • Also effective but has a higher relapse rate

  • Should only be used for the less seriously ill

Outcome

Complications

• Hematogenous spread may ...