Fleas in two Arizona counties are carrying bubonic plague, an infectious disease that took the lives of millions of people in the Middle Ages, according to news reports. Health officials in Navajo and Coconino counties in Arizona recently issued a warning to the general public after fleas in the northern part of the state tested positive for Yersinia pestis, the bacteria that causes the bubonic plague. Humans can contract the plague in a number of ways. In addition to flea bites people can pick up the bacteria by handling the fluids or tissue of a rodent or another animal that has the illness. The plague can also be transmitted through bodily fluids such as respiratory droplets. So far there have been no reported illness or deaths.