Plague: from natural disease to bioterrorism.

Yersinia pestis is the causative agent of plague, an enzootic vectorborne disease usually infecting rodents (rats) and fleas. Humans can become infected after being bitten by fleas that have fed on infected rodents. In humans, the disease usually occurs in the form of bubonic plague. In rare cases, the infection spreads to the lungs via the bloodstream and causes secondary pneumonic plague. Person-to-person transmission has been described for pneumonic plague but is rare in primary bubonic plague. Bubonic plague can usually be treated successfully with antibiotics; however, pneumonic plague develops rapidly and carries a high fatality rate despite immediate treatment with antibiotics. Plague is also recognized as a potential agent of bioterrorism. It has been used, or considered for use, as a biologic weapon on several occasions. It is important for the medical community to be familiar with the epidemiology, diagnosis, and symptoms of plague so it can deliver an appropriate and calm response should the unthinkable happen.