Washington - (Saba):
A new study has revealed that the bacteria that cause plague have evolved to become less virulent over time, allowing them to continue infecting people in three separate pandemics spanning more than a thousand years.
The first pandemic—the Plague of Justinian—struck at the beginning of the Middle Ages in the sixth century and lasted for nearly 200 years.
The Black Death began in the mid-14th century and became the deadliest pandemic in human history, killing up to half the population of Europe, western Asia, and Africa. Outbreaks persisted for centuries.
The third bubonic plague pandemic erupted in China in the 1850s and continues to this day, with some cases recorded in parts of Africa.
"Plague bacteria are particularly important in human history, so it is important to know how these pandemics spread," said Javier Pissarro-Cerda, a microbiologist at France's Pasteur Institute and co-author of the study published in the journal Science on Thursday. In all three cases, the genes of each plague bacterium evolved to become less virulent and less deadly over time, according to the study.
It is believed that by causing less severe infections, the bacteria prolonged the epidemics because they had greater opportunities to spread between people.
The researchers confirmed this theory by infecting mice with modern plague samples, and found that the disease lasted longer when its virulence decreased.
While antibiotics are now able to effectively combat plague, this research may shed light on how other epidemics evolve.
"This allows us to gain a comprehensive understanding of how pathogens adapt to different situations," Pissarro-Cerda said.
"We finally understand better what plague is and how we can develop measures to defend ourselves."
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