Tularemia is an acute febrile zoonosis caused by highly infectious gram-negative coccobacilli. It can present with multiple possible clinical syndromes, depending on the route of infection, and requires a high index of clinical suspicion for diagnosis. Microbiology and epidemiology Francisella tularensis is a small, aerobic, catalase-positive, pleomorphic, gram-negative intra- and extracellular coccobacillus. It is highly infectious, requiring as few as 1 to 10 organisms to cause infection. There are four recognized subspecies of F. tularensis (tularensis [type A], holarctica [type B], mediasiatica, and novicida). F. tularensis type A, which has been described as the more virulent of the subspecies, is found predominantly in North America. F. tularensis type B exists throughout the northern hemisphere.
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