Yersinia pestis (formerly Pasteurella pestis) is a Gram-negative, rod-shaped coccobacillus, a facultative anaerobic bacterium that can infect humans and animals. It causes the deadly disease called bubonic plague (or "the plague" colloquially). Human Y. pestis infection takes three main forms: pneumonic, septicemic, and bubonic plagues. All three forms were responsible for a number of high-mortality epidemics throughout human history, including: the sixth century's Plague of Justinian; the Black Death, which accounted for the death of at least one-third of the European population between 1347 and 1353; and the 19th century's Third Pandemic. These plagues probably originated in China and were transmitted west via trade routes.