Answer: Bacteria
Notes: Recently, a person from northern Arizona, United States, died of pneumonic plague, marking the first such death in the region in 18 years. Plague is an infectious disease caused by the zoonotic bacteria Yersinia pestis. It spreads mainly through flea bites from fleas that fed on infected animals. The disease caused millions of deaths in Europe during the Middle Ages. Today, it is rare but still found in rural parts of the western U.S., Africa, and Asia.
