Which organism does not have a known animal reservoir?

Bordetella pertussis, the causative agent of whooping cough, is characterized by its strict human host specificity. Unlike the other organisms listed, which have known animal reservoirs (e.g., Francisella tularensis in rabbits, Pasteurella multocida in various animals including cats and dogs, and Brucella melitensis primarily found in goats and sheep), Bordetella pertussis does not have an established reservoir in animals. This organism is adapted to humans, relying on human-to-human transmission for its lifecycle. The lack of animal reservoirs underscores Bordetella pertussis's role in human diseases, highlighting its public health significance and the importance of vaccination in the control of whooping cough.