Causative agent of the Black Death (plague), this microbe is a small, coccoid-shaped Gram-negative rod. It is nonmotile and little gas is produced from glucose. Reservoir is the rodent population and vector for transmission is the rat flea. Plague can take three forms: pneumonic, septicemic, and bubonic, all of which have high mortality rates when untreated. Cases occur in the US every year, typically among individuals who have close contact with flea-infected mammals in the Rocky Mountains. Occasional die-offs of prairie dogs in the Texas-New Mexico region have been due to plague outbreaks in those populations.