Scientists have documented the way in which a single gene in the bacterium that causes bubonic plague, Yersinia PestisIt allowed to survive hundreds of years by adjusting their virulence and the time it took to kill their victims, but these plague forms finally extinguished.
A study by researchers from McMaster University and the Institut Pasteur of France, published today in the magazine ScienceIt addresses some fundamental questions related to pandemics: how do human populations enter, cause immense disease and evolve different levels of virulence to persist in populations?
Black death remains the most fatal pandemic in registered human history, killing approximately 30 to 50 percent of the populations of Europe, Western Asia and Africa as it advanced through those regions. Appearing in 14th Centurio resurfaced in waves for more than 500 years, persisting until 1840.
Black death was caused by the same bacteria that caused Justinian’s plague, the first plague pandemic that had broken in the mid -500. The third plague pandemic began in China in 1855 and continues today. Its mortal effects are now more controlled by antibiotics, but they still feel in regions such as Madagascar and the Democratic Republic of the Congo, where cases are regularly informed.
“This is one of the first research studies to directly examine the changes in an ancient pathogen, one that we still see today, in an attempt to understand what promotes virulence, persistence and/or eventual extinction of pandemics,” says Hendrik Poinar, co-senior author of the study, the director of the old McMaster Center and possessor of Michael G. Cresidente of the genetic genetics.
The strains of the Justinian plague were extinguished after 300 years of devastating European and the Middle East populations. The strains of the second pandemic emerged from the populations of infected rodents, causing black death, before breaking into two main lineages. One of these two lineages is the ancestor of all current strains. The other resurfaced for centuries in Europe and finally extinguished in the early nineteenth century.
Using hundreds of samples of old and modern plague victims, the team was projected for a gene known as Pla, a high copy component of Y. Pestis What helps him move through the immune system without detecting lymph nodes before spreading to the rest of the body.
An extensive genetic analysis revealed that its number of copies or the total number of print The genes found in the bacteria had decreased in posterior shoots of the disease, which in turn decreased their mortality by 20 percent and increased the length of their infection, which means that guests lived more before dying. These studies were conducted in bubonic plague mice models.
On the contrary, when the print Gene was in its original number of copies, the disease was much more virulent and killed each of its guests and made much faster.
The scientists also identified a surprising similarity between the trajectories of modern and ancient strains, which evolved independently in similar reductions in print In the later stages of the first and second pandemic, and so far, in three samples of the third pandemic, which are found today in Vietnam.
Both in the pests of Justinian and black death, the evolutionary change occurred approximately 100 years after the first outbreaks. The scientists propose that when the number of copies of the gene fell and the infected rats lived more, they could extend the infection further, ensuring the reproductive success of the pathogen.
“The reduction of print It can reflect the size and changing density of the populations of rodents and humans, “explains Poinar.” It is important to remember that the plague was an epidemic of rats, which were the drivers of epidemics and pandemics. Humans were accidental victims. “
Black rats in cities probably acted as “amplification hosts” due to their high number and proximity to humans. Because black rats are highly susceptible to Y. PestisThe pathogen needed that rats populations remain high enough to supply new hosts for Y. Pestis Persist and allow the pandemic cycle to continue.
However, the printReduced strains finally became extinct, probably reflecting another change in the host-patogen relationship within their surroundings.
When the researchers sought signs of exhaustion in a large set of samples of the third pandemic preserved in a collection in the Institut Pasteur, they found three contemporary strains with print exhaustion.
“Thanks to Our International Collaborators Who Local Monitor Epidemics of Plague Worldwide, We Were Uble to Find the Unique Bacterial Samples used for This Project, Akin to Finding of Three Rare Needles in A Haystack,” Says Javier Pizarro-Cerrdá, co-senior author of the work, director of the work, director of the work, director of the Yersinia Research Unit and the WHO plague center in the Institut Pasteur.
The Institute houses one of the richest collections in the world of modern Y. Pestis Isolated, adds Guillem more Fiol, co-leader of the study of the study and postdoctoral researcher supervised by Pizarro-Cerdá.
“One of the most interesting aspects of our research was the possibility of exploring a characteristic observed for the first time in the extinct plague strains, which, for the first time, could be experimentally tested in contemporary bacterial strains alive,” he says.
“Although our research sheds light on an interesting pattern in the evolutionary history of the plague, most of the strains that continue to circulate today in Africa, South America and India are the most virulent, which were previously responsible for mass mortality,” says Ravneet, co-leader author of the study and doctoral candidate of the DNA center of McMaster Sidhu.