Tularemia

GENERAL PRINCIPLES

• Tularemia is caused by the gram-negative bacteria Francisella tularensis and is endemic to the South Central US. It is associated with exposure to infected animals (particularly rabbits) and transmitted via tick bite or aerosolized droplets.

• F. tularensis is one of the most infectious pathogens known, with as few as 10 organisms necessary to cause disease. Due to its extreme infectivity, ease of dissemination, and capacity to cause illness with subsequent death, tularemia is considered a potential bioterrorism agent.

DIAGNOSIS

Clinical Presentation

Fever and malaise occur 2-5 days after exposure. Three clinical presentations are recognized, depending on the route of transmission: ulceroglandular (painful regional lymphadenitis with a skin ulcer), typhoidal (systemic disease with high fever and hepatosplenomegaly), and pneumonia. Systemic and pneumonic diseases have high mortality if not treated promptly.

Diagnostic Testing

• Culture isolation in blood, sputum, or pleural fluid lacks sensitivity. Before sending specimens, the microbiology laboratory must be notified given the high infectivity of F. tularensis (biosafety level 3 facilities are required).

• Acute and convalescent serologic studies provide a retrospective diagnosis.

TREATMENT

Aminoglycosides are the treatment of choice. Streptomycin 1 g IM q12h or gentamicin 5 mg/kg IV divided q8h for 10 days are preferred. Doxycycline 100 mg IV/PO q12h for 14 days is an alternative but is more likely to result in relapse. Ciprofloxacin 500-750 mg PO q12h for 14-21 days is also an alternative.⁴⁴