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Tiny genetic shift led to ‘The Black Death’ and worse

The research, conducted at the Northwestern University Feinberg School of Medicine, has discovered that a single, tiny genetic change fundamentally altered the bacterium and in doing so affected human history.

The bacterium that causes plague, called Yersinia pestis, began as a common organism found in the intestines of humans and other animals. Through a small genetic change the organism gravitated to become one capable of severe respiratory infection (pneumonic plague) and then, through further modification, it became capable of causing a bubonic plague (so-named named because of the buboes found in body areas like the armpits, upper femoral, groin and neck region.)

Through examination of the development of the bacterium (by comparing the current form of the organism and ancestral strains), researchers have concluded that the main difference between the current strain and closely related strains is a gene for a protein found on the surface membrane of the bacterial cell called Pla.

The importance of this protein as a virulence factor and for the bacterium being able to cause lung infections was verified though animal studies on mice. This was shown by inserting the gene for Pla into similar strains not known to cause lung infections. The profile of these genetically modified bacteria altered, and they were able to infect the mice. Importantly, no other changes to Yersinia were needed in order to trigger lung infection.

Furthermore, a similar small change was all that was required for the organism to shift from a respiratory pathogen (pneumonic plague) to one capable of infecting the lymph nodes and causing probable death (bubonic plague.)

Some pandemics of the disease were so severe as to have affected the course of human history. For instance, during the period of time known as the “Black Death” which began in fourteenth century Europe, over 75 million people worldwide are estimated to have perished.

The new findings are of importance for microbiologists to better predict how the bacterium might adapt in the future and to design strategies to control any potential future outbreaks.

The research has been published in journal Nature Communications. It is titled “Early emergence of Yersinia pestis as a severe respiratory pathogen.”

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Dr. Tim Sandle is Digital Journal's Editor-at-Large for science news. Tim specializes in science, technology, environmental, business, and health journalism. He is additionally a practising microbiologist; and an author. He is also interested in history, politics and current affairs.

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