Tularemia is most commonly caused by infection with which bacterium?

• A. Francisella tularensis
• B. Yersinia pestis
• C. Brucella canis
• D. Listeria monocytogenes

Answer: (A)

Tularemia is caused by infection with Francisella tularensis, a small, highly infectious Gram-negative coccobacillus. This organism is the classic etiologic agent of tularemia, which humans usually acquire through contact with infected wildlife (especially rabbits and rodents), bites from arthropod vectors like ticks or deer flies, inhalation of contaminated aerosols, or ingestion of contaminated water or undercooked meat. Because only a tiny number of bacteria can initiate disease, tularemia can present in multiple forms, such as ulceroglandular, glandular, oculoglandular, or pneumonic disease, depending on the route of exposure.

The other organisms listed are associated with different diseases: Yersinia pestis causes plague, Brucella canis causes brucellosis, and Listeria monocytogenes causes listeriosis. Hence, Francisella tularensis is the correct match for tularemia.