The Plague: The Great Mortality

Madeleine Youngblood

Period 5

Plague, Biology

There are many names for the disease; The Black Death, The Great Mortality, La Pest. [3]. In today’s world, however, most people know it simply as The Plague. The plague, scientifically known as Yersinia Pestis, is a zoonotic, non-motile, non-spore forming bacteria that is classified in humans in three forms; Bubonic, Septicemic, and Pneumonic plague. [3] The plague pathogen has scarred humanity's history, taking over 85 million lives throughout its raging epidemics. [5]. The plague bacteria has been responsible for a number of outbreaks of high mortality rates throughout the early sixth century and even up until today. [5]. Some of the most violent outbreaks occurred in the sixth, fourteenth,

and even nineteenth centuries, claiming millions of lives worldwide. [6]. Today, all humans are at risk, but the treatment for Y. Pestis now provides a much better prognosis for those infected with the pathogen. Most cases of the plague today, according to the WHO, occur in sub-saharan Africa and Madagascar, which make up over 95% of reported cases. [7].

One of the things that made the Plague bacteria so lethal was the fact that no one knew how was the pathogen was spread up until 1894, when the bacteria was found again in Hong Kong.

[5]. Y. Pestis is most often found in fleas, which then are able to be transferred to almost any mammal. [3]. Y. Pestis is able to colonize the midgut of the flea by the actions of YMT (Yersinia Murine Toxin, a plasmid-encoded phospholipase D that, when active, produces an enzyme-catalyzed hydrolysis of phosphodiester bonds) and by the HMS (Hemin Storage System), which synthesizes extracellular polysaccharides, a fundamental component of the production and structure of biofilm. [3]. Essentially, the bacteria is able to thrive in fleas because the bacteria secretes essential substances that both are able to break down the flea’s digestive system as well as maintain the structure and physicochemical properties of biofilm. Luckily, since the discovery and further analysis of the bacteria in the case of the Hong Kong epidemic in 1894, we have learned much more about the bacteria, agencies like the CDC, WHO and NIAID that have worked (and still are working) to eradicate and educate people about the pathogen have developed many treatments. [5]. Treatments for Y. Pestis include antibiotics like Streptomycin, Gentamicin, Ciprofloxacin, and Levofloxacin, as well as a plague vaccine. However, the vaccine is only recommended for those with higher susceptibility rates, such as those who live in Africa,

Asia, and South America. [7].

The bacteria, Yersinia Pestis, causes all three categorizations of the plague, and is a gram-negative, non-motile (only while in a human host), zoonotic, non-spore forming organism.

[11]. Y. Pestis is also categorized as coccobacillus in shape, meaning that it is both slightly rod-shaped (bacillus) as well as spherical (coccus). [11]. One of the major pathogenic factors of Y. Pestis is its ability to produce and secrete polysaccharides, more specifically, lipopolysaccharides (LPS). [8]. Lipopolysaccharides aid greatly in that they elicit a very strong immune response in animals. [8]. Lipopolysaccharides, essential components of which include core oligosaccharides (short chains of sugar residues within gram-negative LPS), lipid components, and O-antigen, play a large role in the bacteria’s ability to colonize the human body and evade immune response. [13]. There are two strains of the bacteria, strain CO96-3188 and strain KIM5(pCD1Ap)+. [11]. There are some minute differences in the gene structure of the two strains, as strain KIM has 4,600,755 base pairs where strain CO96 has 4,653,728, and most of the genetic differences between the two strains are primarily C-G base pair differences. [11]. Many of the genes in both strains have actually become integrated in the gene sequencing of Y. Pestis from different bacteria and viruses.

[11].