The bacteria Yersinia pestis is responsible for causing devastating misery on humankind over the centuries. Due to the bacteria, an estimated 200 million or even more people have died. Not only this, it has also been held responsible for causing the most horrific plagues in the 6th and 14th centuries.

Though it has caused so many problems, it was always not particularly dangerous. On Tuesday, researchers said the bacteria has undergone minor genetic changes many centuries ago, which has turned it from mild to murderous.

The bacterium is responsible for two of the deadliest pandemics in human history:-

1. The 6th decade Justinian Plague- it was named after the Byzantine queen, who was infected, but was able to survive.
2. The 14th Black Death – Rats with fleas carrying the bacteria has spread the plague to people.

As per the US Centers for Disease Control and Prevention, a person can suffer from the bacteria after he has been bitten by a flea carried by a rodent and also when if he is handling the rodent. But, advancements have been made as antibiotics are available that can effectively treat plague today.

Such was not the case in the mid-1300s in which 60% of Europe’s population could not survive due to the germ. Researchers have assessed ancestral strains of Y. pestis in mice, so that they can know when and how the bacterium has evolved.

Upon the assessment, they came to know that gene known as Pla has led the bacteria to become so deadly.