Week Nine: The Black Plague

Common Name: Black Plague, Bubonic Plague

Scientific Name: Yersinia pestis

Not-So-Fun Fact: Yersinia pestis is the bacterium which causes bubonic plague, and was briefly discussed in association with the Oriental Rat Flea. This bacterium builds up in the gut of the flea and causes it to regurgitate the colony into the bloodstream of its victim, spreading the disease. Bubonic plague can cause swollen lymph nodes, necrosis of the flesh, weakness, chills, and death.

Black Plague

Yersinia pestis

Domain: Bacteria

Kingdom: Prokaryotae

Phylum: Proteobacteria

Class: Gammaproteobacteria

Order: Enterobacteriales

Family: Enterobacteriaceae

Genus: Yersinia

Species: Y. pestis

Description: The bacterium itself is a rod-shaped organism that lives in the gut of a flea. For the description of the flea, see Week Five: Oriental Rat Flea.

Environment: The area of the United States inhabited by the hosts of this bacterium is primarily rural areas west of the Rockies. The bacteria usually circulate in an enzootic system among rat and flea populations, spreading to other species only occasionally. Humans usually contract the disease from flea bites contaminated by the pathogen. Once present in the human body, the bacterium moves from the bloodstream to the lymphatic system, where it causes the formation of buboes.

Reproduction & Development: This bacterium undergoes asexual reproduction through the process of binary fission. This quick, simple method of reproduction allows the infamous technique of “blocking” the gut of a flea with the bacterial colony, which forces the partial regurgitation of the colony into the bloodstream of the flea’s victim. During the bacterium’s development it may be passed between fleas and their mammalian hosts many times.

Nutrition: The Black Plague bacterium is a parasite that feeds primarily on fleas and their host rodents, using fleas—usually the Oriental Rat Flea—as a carrier. Rats are the main hosts, but many other species may fall victim to the organism, including squirrels, mice, and chipmunks. Humans are not the preferred host, and especially not for the fleas, but when sudden die-offs of rats occur, the fleas have no choice but to feed off of humans, thus spreading the bacterium to humans. Yersinia pestis is known as a chemoheterotroph, which refers to its reliance on foreign organic molecules for nutrition.