INTRODUCTION

Plague is an acute bacterial infection caused by Yersinia pestis, a member of the family Enterobacteriaceae. Y. pestis is a pleomorphic, nonmotile, nonsporulating, intracellular, gram-negative bacillus that has a characteristic bipolar appearance on Wright, Giemsa, and Wayson's stains. There are three virulent biovars – antiqua, mediaevalis, and orientalis – and a fourth avirulent biovar, microtus. The orientalis biovar is thought to have originated in southern China and caused the most recent pandemic.

The Working Group for Civilian Biodefense considers plague to be a potential biological weapon because of the pathogen's availability “around the world, its capacity for its mass production and aerosol dissemination, and the difficulty in preventing such activities, high fatality rate of pneumonic plague, and potential for secondary spread of cases during an epidemic.” Of the potential ways in which Y. pestis could be used as a biological weapon, aerosol release would be most likely. This method has been successfully demonstrated to cause disease in Rhesus macaques.

EPIDEMIOLOGY

Plague as a Biological Weapon

In the 20th century, countries including the United States, the former Soviet Union, and Japan developed ways for using Y. pestis as a weapon. Creating aerosolized plague is technically challenging; however, if an intentional release of aerosolized plague were to take place, an outbreak of pneumonic plague would be likely. This would be of serious concern because of the high case-fatality rate and the potential for person-to-person transmission.