Tularemia

Key Features

Essentials of Diagnosis

• History of contact with rabbits, other rodents, and biting ticks in summer in endemic area

• Fever, headache, nausea, and prostration

• Papule progressing to ulcer at site of inoculation

• Enlarged regional lymph nodes

• Positive serologic tests or culture of ulcer, lymph node aspirate, or blood

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 aerosol transmission of the organism

• The incubation period is 3–5 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

• A papule at the site of inoculation develops and soon ulcerates

• This local lesion 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 and may suppurate

• Pneumonia may develop from hematogenous spread of the organism or may be primary after inhalation of infected aerosols

• Following ingestion of infected meat or water, an enteric form may be manifested by gastrointestinal symptoms, stupor, and delirium

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

Differential Diagnosis

• Rickettsial and meningococcal infections

• Cat-scratch disease

• Infectious mononucleosis

• Bacterial and fungal diseases

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

Treatment

Medications

• Streptomycin

  • Dosage: 7.5 mg/kg intramuscularly every 12 hours for 7–14 days

  • Drug of choice

• Gentamicin

  • 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 produce meningitis, perisplenitis, pericarditis, pneumonia, and osteomyelitis

References