Plague, a disease of rodents transmitted by fleas, is widespread in the western United States. The epidemic form of the disease has been known since antiquity for the devastation caused by world-sweeping outbreaks such as the "Black Death" in the Middle Ages. Today, improved sanitation practices and rat control have reduced the threat of epidemics in developed countries. Nevertheless, plague is firmly entrenched among wild rodents in North America and individual cases continue to occur among humans exposed to these animals and their fleas.
In Colorado, local health departments and county environmental health officers have training in plague surveillance and control. Their agencies should be contacted whenever your observations, especially large-scale rodent die-offs, arouse suspicions about this disease.