Tularemia is an acute and plaguelike infectious disease caused by the bacterium Francisella tularensis, which is transmitted to humans via the bites of infected bloodsucking insects, direct contact with infected animals, the eating of undercooked meat, or the drinking of contaminated water. The incubation period for the disease is two to ten days. Symptoms include headache, fever, chills, vomiting, and body aches. Antibiotics are used in treatment, most commonly streptomycin.
Although it's not restricted to one animal, most patients are exposed to the disease from contact with rabbits. In Fidelity, the team suspected that the patient had been exposed to it because she cooked rabbits at work. In You Don't Want To Know, the team suspected that a magician had been exposed to it by the rabbits used in his act.