INTRODUCTION

Tularemia is a zoonotic disease caused by Francisella tularensis, a nonsporulating, nonmotile, aerobic, gram-negative coccobacillus. There are several subspecies of F. tularensis, with the biovars tularensis (type A) and holarctica (type B) occurring most commonly in the United States. The clinical syndromes caused by tularemia depend on the route of infection and subspecies of the infecting organism. Tularemia is highly infectious, requiring inhalation or inoculation of as few as 10 organisms to cause disease. Although its virulence factors are not well characterized, type A is generally thought to be the more virulent subspecies. However, the virulence of type A subspecies may vary between geographic regions within the United States, with the midwestern and eastern states having more severe infections.

The Working Group for Civilian Biodefense considers tularemia to be a dangerous potential biological weapon because of its “extreme infectivity, ease of dissemination, and its capacity to cause illness and death.” Of the potential ways that F. tularensis could be used as a biological weapon, an aerosol release is expected to have the most severe medical and public health outcomes.

EPIDEMIOLOGY

Tularemia as a Biological Weapon

Weaponized F. tularensis was developed and stockpiled by the U.S. military, though the supply was destroyed in the 1970s. The Soviet Union is reported to have developed antibiotic- and vaccine-resistant strains of weaponized F. tularensis.

Experts believe that an aerosolized release is the most likely intentional use of F. tularensis organisms.