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The Causative Agent Of The Infamous Bubonic Plague, Primary Septicaemic Plague And Primary Pneumonic Plague

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Yersinia pestis is the causative agent of the infamous bubonic plague, primary septicaemic plague, and primary pneumonic plague. Y. pestis was first discovered by Shibasaburo Kitasato and Alexandre Yersin, but due to Yersin’s description of the bacteria being more accurate, this bacterium was named after him (3). There are still disputes going on for who had correctly identified Y. pestis first. Yersinia pestis belongs to the Enterobacteriaceae bacteria family and is a Gram-negative coccobacillus. It is a non-motile, non-spore forming, facultative anaerobic bacillus that displays bipolar staining with Giemsa, Wayson, or Wright’s staining (2,3,4). Y. pestis grows optimally at 28°C but can grow at 37°C (human hosts). At the latter temperature, different plasmids are expressed to allow it to survive in those conditions, one of them being fraction 1 (F1), a protein capsule (at 28°C, the bacteria does not have a capsule) (5). Transmission of Y. pestis is primarily zoonotic with occasional droplet by aerosol transmission. It normally infects rodents, with humans being accidental hosts. There are at least 73 different genera of mammals and 30 species of fleas that act as reservoirs in nature (2). Humans do not get infected directly by rodents, but rather by intermediate hosts: fleas. The fleas get infected when they ingest blood of an infected animal. The bacteria produce a coagulase that forms a blood clot in the flea, which inhibits them from swallowing. In the flea, they

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