ABSTRACT
Tularemia was reported as a new plague-like disease of California ground squirrels (Citellus spp.) by McCoy in 1911, and the etiological agent Francisella tularensis was isolated in 1912. 1 The disease did circulate much earlier, in both Europe and Asia. 2,3 Subsequently, F. tularensis has been associated with disease in a wider range of animal species than any other zoonotic disease. 4 F. tularensis is considered a potential agent of biological warfare and bioterrorism and as such is classified as a category A select agent and designated as a Tier 1 pathogen. 5–7 The World Health Organization (WHO) and the European Centre for Disease Prevention and Control (ECDC) have categorized F. tularensis as a top-priority pathogen of concern with respect to intentional misuse. 8,9 In this context, respiratory tularemia (acquired through inhalation) is most feared. Natural transmission to humans, however, can also be through food or water, the bite of a blood-feeding arthropod, or by direct contact with infected animals. The infectious dose for humans can be as low as 10–25 bacteria. 10–12 Human-to-human transmission of F. tularensis is exceedingly rare and of little clinical importance. Other Francisella spp. are etiological agents of francisellosis, a disease of fish and molluscs. These Francisella spp. may infect warm water aquaculture fish species including tilapia 13–15 and cold water species such as farmed Atlantic cod. 16–19
