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Comparison between Pneumonic and Bubonic Plagues


Plague is an infectious disease caused by a gram-negative bacterium called Yersinia pestis. The bacterium is carried from dead animals by a flea, which acts as a vector for these diseases. The bacteria are ingested by the Oriental Rat Flea (Xenopsylla cheopis), and the microorganisms reside in its stomach. When this flea bites an animal or human being, such bacteria is regurgitated into the blood of that animal or human being. Once the pathogen gets an entry into the animal blood, it can cause localized or systemic infections.

When the infections are localized in the lymph glands and ducts, it is referred to as bubonic plague; if such organisms are localized and cause infection within the lungs, it is referred to as pneumonic plague. However, if such infections spread into the blood and affects various end organs, it is referred to a systemic infection called septic plague. The infection is caused due to a destruction of phagocytes by these organisms, and the natural defense mechanisms of the body are lost. This may lead to a situation of super-infections when the body becomes prone to infections through other bacterial species. Further, the infection spreads very fast since Yersinia can multiply within the phagocytes of host cells. This article will compare the two forms of pneumonic and bubonic plague.

Pneumonic plague is a severe type of lung infection and is more virulent than bubonic plague. However, bubonic plague may lead to pneumonic plague. Primary pneumonic plague results from inhalation of fine droplets in the air (containing Yersinia), which can be transmitted from one human to another human without involvement of vectors. This form of plague when untreated has a mortality rate of 100%. In secondary pneumonic plague, the pathogens get an entry into the respiratory system from the blood. The major signs are haemoptysis (coughing up blood), headache, weakness, and fever. With the progression of the disease, it leads to respiratory failure and cardiogenic shock. Antibiotics like streptomycin or tetracycline should be administered within 24 hours after detection of such infection.

Bubonic plague definitely results from the bite of the flea Xenopsylla cheopis, which harbors Yersinia in its gut. After three to seven days of exposure, flu-like symptoms develop and include fever, vomiting, and headaches. Lymph glands are swollen across the body and specifically in groins, arm pits, and the neck regions. The lymph nodes are painful and often break open. The painful lymph nodes are called “buboes,” which forms the basis for naming the disease.

A unique feature of the disease (bubonic plague) is the presence of acral gangrene on the fingers, toes, lips, and at the end of upper and lower extremities. Due to gangrene (lack of blood supply), these areas appear blue or black, and necrosis occurs. It is associated with ecchymosis on the forearms, too. The other typical symptoms are hematemesis (vomiting out blood), chills, muscle cramps, and seizures. Vaccines are not available, and streptomycin is administered to treat such infections. A brief comparison is provided below:

Features Pneumonic plague

Bubonic Plague

Causative Agent Yersinia Pestis Yersinia Pestis
Organ System Affected Respiratory System Lymphatic System
Common Locations Lungs Groin, Under the Arms
Ecchymosis and Acral Gangrene Absent Present
Symptoms Haemoptysis, Fever, Headache Hematemesis, Seizures, Chills
Vector Borne No Yes (Through Oriental Rat Flea)
Classification Primary and Secondary One Type
Treatment With Antibiotics Like Streptomycin and Tetracycline With Antibiotics Like Streptomycin and Tetracycline
Mortality Percentage 100% Without Treatment 90% Without Treatment
Virulence High Lower Than Pneumonic Plague
Vaccination Available No No
Swollen Lymph Glands No Yes

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References :

[0]Benedictow, Ole Jørgen (2004). The Black Death, 1346-1353: The Complete History. Boydell & Brewer, pp. 27-28.

[1]Scott, Susan, and C. J. Duncan (2001). Biology of Plagues: Evidence from Historical Populations. Cambridge, UK; New York, NY: Cambridge University Press.


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