Plague

I forget why I looked this up, ages ago, but I was startled to learn that the plague is still pretty active (1-3 thousand cases per year), for a disease that I thought burned itself out after decimating a good chunk of Europe in the 16th and 17th centuries. (By the way, I learned pretty recently that most people use the word "decimate" incorrectly, to describe near-total disasters. It literally means reduce / destroy by 10%, hence the "dec-" in the word. I'm not sure how / why people got in the habit of inflating its meaning.)

The American Centre for Disease Control notes that, within the U.S., the plague is most common in the American Southwest. Which means that you probably shouldn't pet a prairie dog, even if you have the opportunity to do so.