Bubonic Plague
Bubonic Plague Definition
The bubonic plague, also known as bubonic fever, is the best-known variant of the deadly infectious disease caused by the enterobacteria Yersinia pestis (Pasteurella pestis). The epidemiological use of the term ?plague? is currently applied to bacterial infections that cause buboes, although historically the medical use this term has been applied to pandemic infections in general.
Bubonic Plague Historical Background
Generally, after an incubation period of 1-6 days, the history suggests a severe and rapidly progressive sepsis.
Bubonic Plague Pathophysiology
The etiologic agent of the plague is the Y pesti enterobacterias, a facultative anaerobic, intracellular, gram-negative bacillus. The organism can be transmitted from a host to a human via close contact with infected tissue or body fluids, via the bite of a vector, and via direct inhalation of the bacterium. Currently, the most common found form of transmission involves the bite of a vector infected by a host. Infection through inhalation would be of concern if the bacillus was aerosolized. More than 200 different rodents and species can serve as hosts to Y pestis. These include domestic cats and dogs, chipmunks, squirrels, marmots, deer mice, rabbits, hares, rock squirrels, camels, and sheep. The vector is usually Xenopsylla cheopis, a rat flea. Other carriers of plague include human lice and ticks. Rodents that are resistant to the infection form an enzootic stage that ensures the long-term survival of the bacillus. Occasionally, the infected animals are not resistant to the disease and they succumb. This is known as an epizootic stage and ensures the spread of the organism to new areas. A sylvatic stage takes place when humans are infected from wild animals. Three forms of the plague can be found: bubonic plague, pneumonic plague, and septicemic plague. The bubonic form of the plague involves the pathognomonic "bubo" and is a result of deposition of the bacillus in the skin by the bite of an infected vector. If the vector is a flea, bacillus multiples in the flea's esophagus, preventing food entry into the stomach. To avoid starvation, the flea begins a blood-sucking rampage. Between its attempts to swallow, the distended bacillus-packed esophagus recoils, depositing the bacillus into the skin of the victim.
Bubonic Plague Prevalence
A mean of 10-15 cases per year have been reported during the last few decades. One of the largest animal foci of the plague worldwide is found west of the 100th parallel, in states such as Arizona, New Mexico, Colorado, Utah, and California. Only one case of plague imported into the US has been reported since 1926. Most cases take place during the warmer months of the year. In 2006, 13 human plague cases were reported in the United States, the most number of cases since 1994.