Answer:
Humans are its only known host
Explanation:
Humans are not the only known host for bacterium Francisella. For example, Francisella species such as Francisella tularensis uses many other organisms as its host.
Some of the non-human host organisms for Francisella tularensis are wild rabbits, most of the domestic and wild animals. The Francisella tularensis serve as causative agent of tularemia in these organisms which is a plague-like disease.
