Black Death Plague Bacterium Became Less Fatal thanks to Just One Genetic Tweak

image via New Scientist

June 2, 2025, 11:00 AM

• •A genetic change in the plague bacterium Yersinia pestis makes it less deadly but potentially more transmissible.
• •The study found that reduced levels of the pla gene, associated with disease severity, led to mice infected with the reduced- pla strain living longer than those infected with the normal strain.
• •Between 30% and 50% of ancient strains and three modern strains of Y. pestis showed signs of pla depletion.
• •Researchers hypothesize that pla depletion occurred because repeated plague outbreaks decreased rodent population density, allowing for greater disease spread.

A recent study published in Science reveals that a small genetic change in the bacterium Yersinia pestis, which causes the plague, has made it less deadly. This change involves a reduction in the pla gene, which is linked to disease severity. The research team found that mice infected with the reduced- pla strain of the bacterium lived longer compared to those infected with the normal strain. This genetic alteration, prevalent in both ancient and modern strains, suggests that the plague may have evolved to become less lethal but potentially more transmissible, especially in fragmented rodent populations, increasing the chance of disease spread.

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