The black plague, the name by which the disease was called, several times pandemic, which killed between 1347 and 1530 (Lower Middle Ages) about a third of the European population, China and the Middle East, is caused by the bacteria Yersinia pestis.
A Y. pestis is a Gram-negative bacterium, very pathogenic to its hosts that very rarely outlive it. The extreme virulence of this microbe is due, in part, to the variable presence of a molecule on its surface (a lipopolysaccharide), which causes disproportionate activation of the host's immune system.
The immune response to the bacteria is reflected by the high production of substances called cytokines, which cause generalized vasodilation, putting the entire immune system in a state of siege, potentiating septic shock. It has a high resistance to destruction by immune system cells, not only resisting phagocytosis by macrophages but also inducing apoptosis (programmed destruction) of these immune cells.
A Y. pestisit is prepared, adapted, to bypass all immune attack strategies. Furthermore, it causes the destruction of actin filaments, a fundamental protein for muscle function and architecture. Therefore, the progression of the disease irreversibly reduces muscle strength. Tissue breakdown and vasodilation cause numerous hemorrhages which, together with the degeneration of hemoglobin, install a blue-green color that evolves into black, which prints the plague on the skin. The body is dressed in black and cell death plagues the air that can no longer be breathed.
Although its target organ is the lung (which allows the bacteria to be transmitted from person to person through droplets expelled by a sneeze or cough), causing "pseudo-tuberculosis", the disease manifests itself as a zoonosis, appearance of spots and swellings in the armpits and groin, commonly called buboes and hence its name bubonic plague.
This microorganism is transmitted to humans by fleas (Xenopsylla cheopis) that have been in contact with black rats (rattus rattus) and some other infected rodents, animals that are preferential hosts of that pathogen, which is endemic to them and normally fatal.
Fleas are vectors of inter-individual transmission of Y. pestis which, once sucked in with the blood of rodents, multiplies in the insect's intestine. From bite to bite, the flea spreads the bacteria from rodent to rodent, and from these to humans, but also to cats and companion dogs.
It was Paul Louis Simon, in the last decade of the 1894th century, who first identified the flea as the main vector that transmits the disease. The bacterium was first isolated in XNUMX, in Honk Kong, by bacteriologist Alexandre Yersin. Having determined the bacterium's mode of transmission, it became associated with it by giving its name to the pestilential microbe species: Yersinia pestis.
From the above, it is evident that the conditions of hygiene and public health, reduced exposure to infected animals and fleas, or their elimination, are determining factors in controlling the spread of the agent causing the plague.
In Portugal we owe the epidemiological, clinical and bacteriological proof of bubonic plague to Ricardo Jorge. In June 1899, when the third great plague of the plague hit the city of Porto, the action of the patron of Portuguese Public Health prevented the scourge from having been more devastating. However, the implementation of prophylactic actions, such as the evacuation and disinfection of houses, galvanized popular fury which, manipulated and encouraged by some opportunistic political groups of public ignorance, literally forced Ricardo Jorge to flee the city to safeguard his own life.
But there is no longer black plague?! Of course there is!
Over the last 150 years, we have seen significant advances in medical, microbiological and immunological sciences that have allowed us to identify the nature of the microorganisms that cause diseases in us, understand how they spread, their pathogenic mechanisms.
The knowledge acquired enabled the implementation of preventive public health attitudes against the spread of once-fatal microbes, discovering and manufacturing vaccines and antibiotics. These “magic bullets” allow those who have access to them to acquire, in addition to immunity and protection, an idea that the war is won. Nothing more wrong.
The World Health Organization has issued frequent warnings, either for the danger of resurgence of these diseases deemed "extinct" by the "medicated" world, or for the continuation of these diseases in places on the planet where they are the endemic present of human beings who are not have mornings in the future with health.
The Black Death remains endemic in parts of Africa, America and Asia. In 2003, more than 2000 thousand deaths were registered in nine countries alone. The scientific community that follows the Yersinia pestis has been emitting alarm signals (see eg Welch, TJ, PLoS One, March 2007 – http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000309) about the possibility that a multi-antibiotic-resistant strain we know might emerge and revive the pestilential illustrations of death from history books to newspaper covers.
In this context, which is not yet dark for the world more concerned about the public debt in crisis (Europe, United States…), it is important to use the knowledge that the research tools of modern biochemistry allow us to obtain by mapping and analyzing the genome of individuals.
By knowing the genes of the genomic library of a given pathogen, we can better understand how it works, identify the proteins and other biomolecules of its toxicity, reveal its role in the microbial balance necessary for health (let us remember that without bacteria we would not exist as such well illustrates the comic strip on the side!).
Technical advances now allow the collection, recovery and sequencing of DNA (deoxyribonucleic acid, structural and coding molecule of genes) from trace samples, amounts about a million times less than a gram, embedded in inorganic remains (teeth and matrix bone) of victims dead many centuries ago. In the case in the news, they made it possible for researchers to unearth the genes and reconstitute 99,9% of the genome of Y. pestis in a set of four human beings that were buried between 1348 and 1350, in East Smithfield, England.
The results published in the journal Nature (27 October 2011 – http://www.nature.com/nature/journal/v478/n7370/full/nature10549.html) contribute to the importance of paleogenetic studies. Researchers have found that the microbe that wiped out nearly a third of the European population in the late Middle Ages is genetically very identical with its current relatives. This suggests the same pathogenicity between medieval and current variants of Yersinia spp. Other factors, such as living conditions, public hygiene, among others, will have been decisive for the medieval pestilential calamity.
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Text from: Antonio Piedade
Biochemical
Science Coordinator in the Regional Press – Ciência Viva
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