Pieter Brughel des älteren / Wikimedia
Triunfo from Death – Peste Negra, De Pieter Brughel des älteren
A single gene can help explain the persistence of the plague throughout human history. Changes on a single gene of the plague bacteria genome allowed to clarify a method that the germ used to survive and spread over time.
Responsible for the deadliest pandemic in history, the bacteria that causes the plague, the Yersinia pestis; It has existed in different strains, from antiquity to our day.
Now, a study this Thursday in Science finally revealed how the adaptations in a single gene helped plague survive during millennia.
As described, the Y. Pestis It has been infecting humans even before there are historical records. The most common form of the disease is known as “Bubonic”. Most of the time, it enters the body through infected fleas bites, although people can catch it directly from infected animals, including rats and cats.
Once inside the body, the bacteria moves to the lymphatic ganglia and replica. As it multiplies, it triggers the formation of “bubões” painful and full of pus, which give rise to the name of the “bubonic plague.”
The plague bacteria can also cause a blood infection, called Plague SEPTICEMICand a pulmonary infection, called plague pneumonic.
The three largest plague pandemics – plague of Justinian (between 542 and 750 AD), black plague (14th century) and plague of Yunnan (from 1855 to 1960) and are among the more deadly outbreaks in the history of humanity.
Beyond the impressive number of deaths associated with the pathogen agent, which is perhaps more remarkable in Y. Pestis is the longevity of its strains.
To investigate the set of genetic tools that the Y. Pestis uses to persist for so long, the researchers made an analysis of a plague gene known as pla in hundreds of samples collected from old and modern victims of the disease.
O gene pla encodes an enzyme that helps Y. Pestis moving through the body without being detected by the host’s immune system.
Previous studies suggested that the pla It’s a key factor which modulates both the lethality of a given strain of the plague and its ability to trigger outbreaks in humans.
However, a plague strain can carry a different number of genes pla than the other; And until then, it was unclear how this number of copies could affect its biology.
In the old plague genomes they analyzed – 20 of which dated the first plague pandemic and 94 of the second – the researchers observed a standard in which Plague strains lost copies of pla over timenamely in the posterior phases of each pandemic.
Among modern genomes, they found three strains that suggest that the same standard is currently unfolding.
The researchers theorized that this adaptation will have made infections less virulent, or harmful to the host body over time. This suggests that evolutionary change has helped the disease keep its hosts – whether rats or human – alive for longer – allowing, on the other hand, that it spread more widely.
