To find out, a team led by Wyndham Lathem, an assistant professor in microbiology-immunology at Northwestern University’s Feinberg School of Medicine in Chicago, examined ancestral strains of Y. pestis in mice.
Advertisement
“If we take the most ancestral [sample] that is known to exist, and we give it the gene for PLA, it can suddenly cause pneumonic plague indistinguishable from modern [Y.] pestis“, Lathem said. The biggest difference they found between this strain and closely related strains that could cause pneumonic plague was a gene for the surface protein Pla.
The evolution of this pathogen may be only about 5 to 10,000 years ago and the earlier version of the bacteria produced only mild symptoms in people who were infected with the microorganism.
Previously only causing gastrointestinal infections when Yersinia Pestis acquired the Pla gene it started causing the fatal pneumonic plague. But researchers have recently said that this bacteria has undergone multiple genetic changes a few centuries ago and this has made it be become murderous. This was shown by inserting the gene for Pla into similar strains not known to cause lung infections.
Studying the mouse models they determined that the ancestral bacteria could colonize the lung but was not the cause of the deadly infection that pneumonic plague is.
Tracing the plague The bacterium Yersinia pestis has inflicted nearly unimaginable misery upon humankind over the centuries, killing an estimated 200 million or more people and triggering horrific plagues in the 6th and 14th centuries.
Earlier studies had shown that this amino acid mutation slightly changes the activity of PLA, but that work had been done only in test tubes, Lathem said.
The bubonic plague was not deadly until the bacteria acquired certain mutations.
“It turns out that the ancestral variant of PLA reduces the ability of the bacteria to get into the deeper tissues by about 100 times compared to the modern variant”, Lathem said. According to Lathem, the surprising conclusion from this aspect of the study is that, contrary to current thinking in the field, Y. pestis may have first evolved as a respiratory pathogen before it could cause the more common form of disease, bubonic plague. [7 Devastating Infectious Diseases]. But with the new mutation, it could infect people at a fast and furious pace, causing pandemics, the researchers said.
That would mean it could have occurred in the century before the Justinian Plague. Importantly, no other changes to Yersinia were needed in order to trigger lung infection.
Advertisement
As per the United States 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. “It’s still circulating out here in the wild”.
