Septicemic plague occurs if bubonic plague is left untreated, or it can occur directly if the disease enters the bloodstream. Septicemic plague causes bleeding into the organs. The name comes from septicemia, which refers to a serious blood infection.

An Arizona resident has died from pneumonic plague, a rare but highly dangerous lung infection, Coconino County health officials confirmed on Friday. This incident marks the first death from the disease in the county since 2007,

Pneumonic plague is both “the least common and most dangerous type of plague,” according to the Cleveland Clinic.