Common themes include the breakdown of society, institutions, and individuals during the plague, the cultural and psychological existential confrontation with mortality, and the allegorical use of the plague about contemporary moral or spiritual questions. Biological warfare
Some of the earliest instances of biological warfare were said to have been products of the plague, as armies of the 14th century were recorded catapulting diseased corpses over the walls of towns and villages to spread the pestilence. This was done by Jani Beg when he attacked the city of Kaffa in 1343.Later, plague was used during the Second Sino-Japanese War as a bacteriological weapon by the Imperial Japanese Army. These weapons were provided by Shirō Ishiis units and used in experiments on humans before being used on the field. For example, in 1940, the Imperial Japanese Army Air Service bombed Ningbo with fleas carrying the bubonic plague. During the Khabarovsk War Crime Trials, the accused, such as Major General Kiyoshi Kawashima, testified that, in 1941, 40 members of Unit 731 air-dropped plague-contaminated fleas on Changde. These operations caused epidemic plague outbreaks. Continued research
Substantial research has been done regarding the origin of the plague and how it traveled through the continent. Mitochondrial DNA of modern rats in Western Europe indicated that these rats came from two different areas, one being Africa and the other being unclear of a specific origin. The research regarding this pandemic has greatly increased with technology.
The flea is parasitic on house and field rats and seeks out other prey when its rodent hosts die. Rats were an amplifying factor to bubonic plague due to their common association with humans as well as the nature of their blood. The rats blood allowed the rat to withstand a major concentration of the plague. The bacteria form aggregates in the gut of infected fleas and this results in the flea regurgitating ingested blood, which is now infected, into the bite site of a rodent or human host. Once established, bacteria rapidly spread to the lymph nodes and multiply. The fleas that transmit the disease only directly infect humans when the rat population in the area is wiped out from a mass infection. Furthermore, in areas of a large population of rats, the animals can harbor low levels of the plague infection without causing human outbreaks. With no new rat inputs being added to the population from other areas, the infection would only spread to humans in very rare cases of overcrowding. Signs and symptoms
After being transmitted via the bite of an infected flea, the Y. pestis bacteria become localized in an inflamed lymph node, where they begin to colonize and reproduce. Infected lymph nodes develop hemorrhages, which result in the death of tissue.Y. pestis bacilli can resist phagocytosis and even reproduce inside phagocytes and kill them. As the disease progresses, the lymph nodes can hemorrhage and become swollen and necrotic. Bubonic plague can progress to lethal septicemic plague in some cases.