| Abstract ---Plague is 
a zoonotic illness caused by the Gram-negative bacillus Yersinia pestis. Human 
are not necessary for persistence of the organism, and we acquire plague from 
animal fleas, contact with infected animals or rarely from other humans via aerosols 
or direct contact with infected secretions. To be able to differentiate endemic 
plague from plague used in biological warfare, medical officers must understand 
the typical way in which humans contract plague in nature: First, a die-off of 
animals in the mammalian reservoir that harbors bacteria-infected fleas will occur. 
Second, troops who have been in close to infected mammals will become infected. 
By contrast, plague will spread via aerosols in the most likely biological warfare. 
A rapid person to person spread of fulminant pneumonia would then occur. If an 
enemy force is to release fleas infected with Y pestis, then people would present 
with classic bubonic plague before a die-off in the local mammalian reservoirs 
occur. The three clinical forms of human plague are bubonic, septicemic and pneumonic. 
Bubonic plague, characterized by painful lymphadenopathy and severe constitutional 
symptoms of fever, chills and headache, is the most common form. Septicemic plague 
without localized lymphadenopathy occurs less commonly and is difficult to diagnose. 
Primary pneumonic plague is spread by airborne transmission and has the highest 
mortality. Diagnosis is established by identifying the organism from blood or 
other body fluids. Patients should be isolated initially and treated with antibiotics 
(streptomycin preferably) early. A killed, whole-cell vaccine is available to 
protect humans against bubonic plague, but not against for primary pneumonic plague. 
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