Figure 5-12. Two common domestic rats.
5-35. PLAGUE (BLACK DEATH)
a. General. Plague is a severe, acute infectious disease caused by the bacillus
Yersinia pestis. It was known in the 14th century as the "Black Death,' which decimated
the human population of Europe. Plague has four major clinical forms: bubonic,
septicemic, pneumonic, and tonsillar septicemic. The latter two forms occur primarily
(1) Transmission. Transmission to man is usually by the bite of a rat flea and
normally results in bubonic or septicemic plague. Either type of infection may progress
into pneumonic plague. Droplets of sputum from patients with pneumonic plague, if
inhaled, may result in primary pneumonic plague. Rarely, bubonic or septicemic
plague may be contracted through minor skin abrasions when there is contact with
(2) Locations. Plague is scattered widely, but unevenly, in endemic foci
throughout India, China, USSR, Mongolia, parts of Southern Asia and the western
United States. It has occurred in South Vietnam since 1962 in epidemic proportions.
(3) Incubation period/treatment. The incubation period of all forms of the
disease is usually six days or less, though rarely, incubation periods of 10 days have
been reported. Once the most dreaded of diseases, plague today--if treated promptly
and adequately--is a curable disease in all of its clinical forms.