An analysis carried out on 25 skeletons of plague victims discovered by railway engineers beneath London last year, has revealed that the Black Death was even more lethal than previously thought. Scientists are now doubtful that the epidemic was spread by the bites of infected fleas living on rats. Instead, it appears that the pathogen mutated into a more virulent strain that was airborne.
The Black Death arrived in Britain from central Asia in the autumn of 1348 and by late spring the following year it had killed six out of every 10 people in London. It was one of the most devastating pandemics in human history, resulting in the deaths of an estimated 75 to 200 million people.
An analysis on the DNA extracted from the 14 th century skeletons unearthed in London revealed traces of Yersinia pestis bacterium, the pathogen responsible for the Black Death , confirming what scientists had suspected – the remains belonged to plague victims who had been hastily buried in a mass grave. Guided by underground radar scans, researchers now plan to expand their search for more victims as it is believed there could be hundreds if not thousands more nearby.
Traces of Yersinia pestis were found in the 14 th century skeletons. Photo source .
Scientists compared the strain of the plague preserved in the victims, to a strain that was recently responsible for killing 60 people in Madagascar. To their surprise, the 14th-century strain, was no more virulent than today's disease. That means that there must have been another factor that caused the 14 th-century strain to become a deadly pandemic, while the Madagascar one did not.
The findings cast doubt on the ‘facts’ that every schoolchild has learned for decades – the Black Death was caused by a highly contagious strain spread by fleas on rats.
“As an explanation for the Black Death in its own right, [bubonic plague is] simply not good enough,” said Dr Tim Brooks, an expert in infectious diseases at Public Health England. “It cannot spread fast enough from one household to the next to cause the huge number of cases that we saw during the Black Death epidemics.”
The Black Death was one of the most deadly pandemics in recorded history. Image source .
Scientists working at Public Health England have therefore suggested a different cause - for any plague to spread at such a pace it must have got into the lungs of victims who were malnourished and then spread by coughs and sneezes – fatal in medieval Europe’s crowded cities. It was therefore a pneumonic plague rather than a bubonic plague, which had a much lower survival rate and could kill within 24 hours.
“In a small number of people … the organism will spread to their lungs and they will then develop a pneumonia,” said Dr Brooks. “It is that critical switch, that if there were enough people in contact with them, that allows it to spread as a pneumonic plague.”
The results of the study have led to a breakthrough in our understanding of the ancient pandemic of the 14 th century, and offers new hope in the understanding of how plagues evolve and spread over the centuries.
Featured image: Black Death at Tourinai, 1349. Image source .
Mass Grave Shows the Black Death’s ‘Catastrophic’ Impact in Rural England
In the summer of 1348, the Black Death arrived in southwest England. The deadly disease rapidly swept through the country, ultimately killing between one-third and one-half of its population. Now, a team of researchers writing in the journal Antiquity has revealed new details about a mass grave of probable Black Death victims buried in the English countryside. The discovery offers rare insight into the plague’s “catastrophic” impact on rural communities.
The grave, located on the grounds of the historic Thornton Abbey in North Lincolnshire, was first excavated in 2013. Archaeologists unearthed the remains of at least 48 individuals, including 27 children. Differences in levels between the rows of bodies suggest the grave was “filled over the course of several days or weeks,” according to the study’s authors. Radiocarbon dating of two skeletons indicated the victims died sometime between 1295 and 1400, while ceramics and two silver pennies found in the grave helped experts narrow the date range down to the mid-14th century.
Though the researchers acknowledge that any number of factors could have driven the mass fatality in Lincolnshire, they suspect the Black Death is the “most probable cause.” Documentary evidence indicates the bubonic plague had hit Lincolnshire by the spring of 1349. What’s more, centuries-old DNA extracted from the teeth of 16 individuals buried at the site revealed the presence of Yersinia pestis, the bacterium that causes the disease.
The skeletons’ ages—which ranged from 1 year old to over 45—lend further credence to the theory that something devastating was at play. Hugh Willmott, a senior lecturer in European historical archaeology at the University of Sheffield and leader of the excavation, tells Live Science’s Mindy Weisberger that medieval cemeteries are typically dominated by very young and relatively old individuals, who are particularly susceptible to disease and injury.
“But what we’ve got is not that profile at all,” says Willmott. “We can tell from the proportion of individuals that everyone is being affected, and everyone is dying.”
Despite the Black Death’s seismic impact on medieval England’s population and society, graves filled with plague victims are quite rare. The best-known examples come from two 14th-century mass graves in London, “where the civic authorities were forced to open new emergency burial grounds to cope with the very large numbers of the urban dead,” explains Willmott in a statement.
Researchers once thought that rural villages with sparser populations were able to cope with the number of plague victims by burying the dead in separate churchyard graves, just as they would have done under less extreme circumstances. But the mass grave in Lincolnshire—which, according to the study authors, “represents the first Black Death mass grave found in Britain in a non-urban context”—suggests country dwellers were also overwhelmed by the Black Death’s toll.
Crucially, the researchers suspect that a hospital run by the clergy of Thornton Abbey was located just outside of the monastery’s walls records from 1322 reference the building, and the remains of a structure discovered south of the grave might represent the spot where the hospital once stood. If many people died at the facility during the Black Death outbreak, clergymen may have struggled to cope, opting for a communal grave instead of distinct burials. The location of the grave also suggests that something was profoundly amiss. Normally, Willmott tells Esther Addley of the Guardian, Lincolnshire’s dead would have been buried in a nearby parish graveyard.
“[P]erhaps the priest or the gravedigger has died—[so] you turn to the church, the canons at the abbey down the road,” the archaeologist explains.
The Lincolnshire grave thus seems to represent a “catastrophic failure of the established system of dealing with the dead,” according to the study. Rather poignantly, however, the burials were far from haphazard. Based on the compression of the skeletons’ shoulders, the researchers think the bodies were wrapped in shrouds, then carefully arrayed in eight rows.
“They are trying to treat them as respectfully as possible, because in the middle ages it’s very important to give the dead a proper burial,” Willmott tells the Guardian. “Even though it is the height of a terrible disaster, they are taking as much care as they can with the dead.”
Several possible causes have been advanced for the Black Death the most prevalent is the bubonic plague theory.  Efficient transmission of Yersinia pestis is generally thought to occur only through the bites of fleas whose mid guts become obstructed by replicating Y. pestis several days after feeding on an infected host. This blockage results in starvation and aggressive feeding behaviour by fleas that repeatedly attempt to clear their blockage by regurgitation, resulting in thousands of plague bacteria being flushed into the feeding site, infecting the host. However, modelling of epizootic plague observed in prairie dogs, suggests that occasional reservoirs of infection such as an infectious carcass, rather than "blocked fleas" are a better explanation for the observed epizootic behaviour of the disease in nature. 
One hypothesis about the epidemiology—the appearance, spread, and especially disappearance—of plague from Europe is that the flea-bearing rodent reservoir of disease was eventually succeeded by another species. The black rat (Rattus rattus) was originally introduced from Asia to Europe by trade, but was subsequently displaced and succeeded throughout Europe by the bigger brown rat (Rattus norvegicus). The brown rat was not as prone to transmit the germ-bearing fleas to humans in large die-offs due to a different rat ecology.   The dynamic complexities of rat ecology, herd immunity in that reservoir, interaction with human ecology, secondary transmission routes between humans with or without fleas, human herd immunity, and changes in each might explain the eruption, dissemination, and re-eruptions of plague that continued for centuries until its unexplained disappearance.
Signs and symptoms of the three forms of plague Edit
The plague comes in three forms and it brought an array of signs and symptoms to those infected. The classic sign of bubonic plague was the appearance of buboes in the groin, the neck, and armpits, which oozed pus and bled. Most victims died within four to seven days after infection. The septicaemic plague is a form of "blood poisoning", and pneumonic plague is an airborne plague that attacks the lungs before the rest of the body.
The bubonic plague was the most commonly seen form during the Black Death. The bubonic form of the plague has a mortality rate of thirty to seventy-five percent and symptoms include fever of 38–41 °C (101–105 °F), headaches, painful aching joints, nausea and vomiting, and a general feeling of malaise. The second most common form is the pneumonic plague and has symptoms that include fever, cough, and blood-tinged sputum. As the disease progressed, sputum became free flowing and bright red and death occurred within 2 days. The pneumonic form of the plague has a high mortality rate at ninety to ninety-five percent. Septicemic plague is the least common of the three forms, with a mortality rate close to one hundred percent. Symptoms include high fevers and purple skin patches (purpura due to DIC). Both pneumonic and septicemic plague can be caused by flea bites when the lymph nodes are overwhelmed. In this case they are referred to as secondary forms of the disease.
David Herlihy  identifies from the records another potential sign of the plague: freckle-like spots and rashes. Sources from Viterbo, Italy refer to "the signs which are vulgarly called lenticulae", a word which bears resemblance to the Italian word for freckles, lentiggini. These are not the swellings of buboes, but rather "darkish points or pustules which covered large areas of the body".
The uncharacteristically rapid spread of the plague could be due to respiratory droplet transmission, and low levels of immunity in the European population at that period. Historical examples of pandemics of other diseases in populations without previous exposure, such as smallpox and tuberculosis transmitted by aerosol amongst Native Americans, show that the first instance of an epidemic spreads faster and is far more virulent than later instances among the descendants of survivors, for whom natural selection has produced characteristics that are protective against the disease. [ citation needed ]
Molecular evidence for Y. pestis Edit
In 2000, Didier Raoult and others reported finding Y. pestis DNA by performing a "suicide PCR" on tooth pulp tissue from a fourteenth-century plague cemetery in Montpellier.  Drancourt and Raoult reported similar findings in a 2007 study. 
However, other researchers argued the study was flawed and cited contrary evidence. In 2003, Susan Scott of the University of Liverpool argued that there was no conclusive reason to believe the Montpellier teeth were from Black Death victims.  Also in 2003, a team led by Alan Cooper from Oxford University tested 121 teeth from sixty-six skeletons found in 14th century mass graves, including well-documented Black Death plague pits in East Smithfield and Spitalfields. Their results showed no genetic evidence for Y. pestis, and Cooper concluded that though in 2003 "[w]e cannot rule out Yersinia as the cause of the Black Death . right now there is no molecular evidence for it."    Other researchers argued that those burial sites where Y. pestis could not be found had nothing to do with the Black Death in the first place. 
In October 2010 the journal PLoS Pathogens published a paper by Haensch et al. (2010),  a multinational team that investigated the role of Yersinia pestis in the Black Death. The paper detailed the results of new surveys that combined ancient DNA analyses and protein-specific detection which were used to find DNA and protein signatures specific for Y. pestis in human skeletons from widely distributed mass graves in northern, central and southern Europe that were associated archaeologically with the Black Death and subsequent resurgences. The authors concluded that this research, together with prior analyses from the south of France and Germany
". ends the debate about the etiology of the Black Death, and unambiguously demonstrates that Y. pestis was the causative agent of the epidemic plague that devastated Europe during the Middle Ages."
Significantly, the study also identified two previously unknown but related clades (genetic branches) of the Y. pestis genome that were associated with distinct medieval mass graves. These were found to be ancestral to modern isolates of the modern Y. pestis strains Orientalis and Medievalis, suggesting that these variant strains (which are now presumed to be extinct) may have entered Europe in two distinct waves.
The presence of Y. pestis during the Black Death and its phylogenetic placement was definitely established in 2011 with the publication of a Y. pestis genome using new amplification techniques used on DNA extracts from teeth from over 100 samples from the East Smithfield burial site in London.   
Surveys of plague pit remains in France and England indicate that the first variant entered western Europe through the port of Marseilles around November 1347 and spread through France over the next two years, eventually reaching England in the spring of 1349, where it spread through the country in three successive epidemics. However, surveys of plague pit remains from the Netherlands town of Bergen op Zoom showed that the Y. pestis genotype responsible for the pandemic that spread through the Low Countries from 1350 differed from that found in Britain and France, implying that Bergen op Zoom (and possibly other parts of the southern Netherlands) was not directly infected from England or France in AD 1349, suggesting that a second wave of plague infection, distinct from those in Britain and France, may have been carried to the Low Countries from Norway, the Hanseatic cities, or another site. 
Vectors of Y. pestis Edit
Historians who believe that the Black Death was indeed caused by bubonic plague have put forth several theories questioning the traditional identification of Rattus sp. and their associated fleas as plague's primary vector.
A 2012 report from the University of Bergen acknowledges that Y. pestis could have been the cause of the pandemic, but states that the epidemiology of the disease is different, most importantly the rapid spread and the lack of rats in Scandinavia and other parts of Northern Europe. R. rattus was present in Scandinavian cities and ports at the time of the Black Death but was not found in small, inland villages. Based on archaeological evidence from digs all over Norway, the black rat population was present in sea ports but remained static in the cold climate and would only have been sustained if ships continually brought black rats and that the rats would be unlikely to venture across open ground to remote villages. It argues that while healthy black rats are rarely seen, rats suffering from bubonic plague behave differently from healthy rats where accounts from warmer climates mention rats falling from roofs and walls and piling high in the streets, Samuel Pepys, who described trifling observations and events of the London plague of 1665 in great detail, makes no mention of sick or dead rats, nor does Absalon Pederssøn in his diary, which contains detailed descriptions of a plague epidemic in Bergen in 1565. Ultimately, Hufthammer and Walløe offer the possibility of human fleas and lice in place of rats. 
University of Oslo researchers concluded that Y. pestis was likely carried over the Silk Road via fleas on giant gerbils from Central Asia during intermittent warm spells.  
Michael McCormick, a historian supporting bubonic plague as the Black Death, explains how archaeological research has confirmed that the black or "ship" rat (Rattus rattus) was already present in Roman and medieval Europe. Also, the DNA of Y. pestis has been identified in the teeth of the human victims, the same DNA which has been widely believed to have come from the infected rodents.  Pneumonic expression of Y. pestis can be transmitted by human-to-human contact, but McCormick states that this does not spread as easily as previous historians have imagined. According to him, the rat is the only plausible agent of transmission that could have led to such a wide and quick spread of the plague. This is because of rats' proclivity to associate with humans and the ability of their blood to withstand very large concentrations of the bacillus.  When rats died, their fleas (which were infected with bacterial blood) found new hosts in the form of humans and animals. The Black Death tapered off in the eighteenth century, and according to McCormick, a rat-based theory of transmission could explain why this occurred. The plague(s) had killed a large portion of the human host population of Europe and dwindling cities meant that more people were isolated, and so geography and demography did not allow rats to have as much contact with Europeans. Greatly curtailed communication and transportation systems due to the drastic decline in human population also hindered the replenishment of devastated rat colonies.  [ clarification needed ]
Evidence against Y. pestis Edit
Although Y. pestis as the causitive agent of plague is widely accepted, recent scientific and historical investigations have led some researchers to doubt the long-held belief that the Black Death was an epidemic of bubonic plague. The arguments are based on differences in mortality levels, disease diffusion rates, rat distribution, flea reproduction and climate, and distribution of human population. 
In 1984, Graham Twigg published The Black Death: A Biological Reappraisal, where he argued that the climate and ecology of Europe and particularly England made it nearly impossible for rats and fleas to have transmitted bubonic plague. Combining information on the biology of Rattus rattus, Rattus norvegicus, and the common fleas Xenopsylla cheopis and Pulex irritans with modern studies of plague epidemiology, particularly in India, where the R. rattus is a native species and conditions are nearly ideal for plague to be spread, Twigg concludes that it would have been nearly impossible for Yersinia pestis to have been the causative agent of the plague, let alone its explosive spread across Europe. Twigg also shows that the common theory of entirely pneumonic spread does not hold up. He proposes, based on a reexamination of the evidence and symptoms, that the Black Death may actually have been an epidemic of pulmonary anthrax caused by Bacillus anthracis.
In 2002, Samuel K. Cohn published the controversial article, “The Black Death: End of the Paradigm”.  Cohn argues that the medieval and modern plagues were two distinct diseases differing in their symptoms, signs, and epidemiologies.  Cohn's argument that medieval plague was not rat-based is supported by his claims that the modern and medieval plagues occurred in different seasons (a claim supported in a 2009 article by Mark Welford and Brian Bossak  ), had unparalleled cycles of recurrence, and varied in the manner in which immunity was acquired. The modern plague reaches its peak in seasons with high humidity and a temperature of between 50 °F (10 °C) and 78 °F (26 °C), as rats' fleas thrive in this climate.  In comparison, the Black Death is recorded as occurring in periods during which rats' fleas could not have survived, i.e. hot Mediterranean summers above 78 °F (26 °C).  In terms of recurrence, the Black Death on average did not resurface in an area for between five and fifteen years after it had occurred.  In contrast, modern plagues often recur in a given area yearly for an average of eight to forty years. Last, Cohn presents evidence displaying that individuals gained immunity to the Black Death, unlike the modern plague, during the fourteenth century. He states that in 1348, two-thirds of those suffering from plague died, in comparison to one-twentieth by 1382.  Statistics display that immunity to the modern plague has not been acquired in modern times.
In the Encyclopedia of Population,  Cohn points to five major weaknesses in the bubonic plague theory:
- very different transmission speeds – the Black Death was reported to have spread 385 km in 91 days (4.23 km/day) in 664, compared to 12–15 km a year for the modern bubonic plague, with the assistance of trains and cars
- difficulties with the attempt to explain the rapid spread of the Black Death by arguing that it was spread by the rare pneumonic form of the disease – in fact this form killed less than 0.3% of the infected population in its worst outbreak (Manchuria in 1911)
- different seasonality – the modern plague can only be sustained at temperatures between 10 and 26 °C and requires high humidity, while the Black Death occurred even in Norway in the middle of the winter and in the Mediterranean in the middle of hot dry summers
- very different death rates – in several places (including Florence in 1348) over 75% of the population appears to have died in contrast the highest mortality for the modern bubonic plague was 3% in Bombay in 1903
- the cycles and trends of infection were very different between the diseases – humans did not develop resistance to the modern disease, but resistance to the Black Death rose sharply, so that eventually it became mainly a childhood disease
Cohn also points out that while the identification of the disease as having buboes relies on accounts of Boccaccio and others, they described buboes, abscesses, rashes and carbuncles occurring all over the body, the neck or behind the ears. In contrast, the modern disease rarely has more than one bubo, most commonly in the groin, and is not characterised by abscesses, rashes and carbuncles. This difference, he argues, ties in with the fact that fleas caused the modern plague and not the Black Death. Since flea bites do not usually reach beyond a person's ankles, in the modern period the groin was the nearest lymph node that could be infected. As the neck and the armpit were often infected during the medieval plague, it appears less likely that these infections were caused by fleas on rats. 
Ebola-like virus Edit
In 2001, Susan Scott and Christopher Duncan, respectively a demographer and zoologist from Liverpool University, proposed the theory that the Black Death might have been caused by an Ebola-like virus, not a bacterium. Their rationale was that this plague spread much faster and the incubation period was much longer than other confirmed Y. pestis–caused plagues. A longer period of incubation will allow carriers of the infection to travel farther and infect more people than a shorter one. When the primary vector is humans, as opposed to birds, this is of great importance. Epidemiological studies suggest the disease was transferred between humans (which happens rarely with Yersinia pestis and very rarely for Bacillus anthracis), and some genes that determine immunity to Ebola-like viruses are much more widespread in Europe than in other parts of the world. Their research and findings are thoroughly documented in Biology of Plagues.  More recently the researchers have published computer modeling  demonstrating how the Black Death has made around 10% of Europeans resistant to HIV.
In a similar vein, historian Norman Cantor, in In the Wake of the Plague: The Black Death and the World It Made (2001), suggests the Black Death might have been a combination of pandemics including a form of anthrax, a cattle murrain. He cites many forms of evidence including: reported disease symptoms not in keeping with the known effects of either bubonic or pneumonic plague, the discovery of anthrax spores in a plague pit in Scotland, and the fact that meat from infected cattle was known to have been sold in many rural English areas prior to the onset of the plague. The means of infection varied widely, with infection in the absence of living or recently dead humans in Sicily (which speaks against most viruses). Also, diseases with similar symptoms were generally not distinguished between in that period (see murrain above), at least not in the Christian world Chinese and Muslim medical records can be expected to yield better information which however only pertains to the specific disease(s) which affected these areas.
Cutaneous anthrax infection in humans shows up as a boil-like skin lesion that eventually forms an ulcer with a black center (eschar), often beginning as an irritating and itchy skin lesion or blister that is dark and usually concentrated as a black dot. Cutaneous infections generally form within the site of spore penetration between two and five days after exposure. Without treatment about 20% of cutaneous skin infection cases progress to toxemia and death.  Respiratory infection in humans initially presents with cold or flu-like symptoms for several days, followed by severe (and often fatal) respiratory collapse. Historical mortality was 92%.  Gastrointestinal infection in humans is most often caused by eating anthrax-infected meat and is characterized by serious gastrointestinal difficulty, vomiting of blood, severe diarrhea, acute inflammation of the intestinal tract, and loss of appetite. After the bacteria invades the bowel system, it spreads through the bloodstream throughout the body, making more toxins on the way. 
Black Death Study Shows Europeans Lived Longer After 14th Century Pandemic
The Black Death, a plague that first devastated Europe in the 1300s, had a silver lining. After the ravages of the disease, surviving Europeans lived longer, a new study finds.
An analysis of bones in London cemeteries from before and after the plague reveals that people had a lower risk of dying at any age after the first plague outbreak compared with before. In the centuries before the Black Death, about 10 percent of people lived past age 70, said study researcher Sharon DeWitte, a biological anthropologist at the University of South Carolina. In the centuries after, more than 20 percent of people lived past that age.
"It is definitely a signal of something very important happening with survivorship," DeWitte told Live Science. [Images: 14th-Century Black Death Graves]
The plague years
The Black Death, caused by the Yersinia pestis bacterium, first exploded in Europe between 1347 and 1351. The estimated number of deaths ranges from 75 million to 200 million, or between 30 percent and 50 percent of Europe's population. Sufferers developed hugely swollen lymph nodes, fevers and rashes, and vomited blood. The symptom that gave the disease its name was black spots on the skin where the flesh had died.
Scientists long believed that the Black Death killed indiscriminately. But DeWitte's previous research found the plague was like many sicknesses: It preferentially killed the very old and those already in poor health.
That discovery raised the question of whether the plague acted as a "force of selection, by targeting frail people," DeWitte said. If people's susceptibility to the plague was somehow genetic — perhaps they had weaker immune systems, or other health problems with a genetic basis — then those who survived might pass along stronger genes to their children, resulting in a hardier post-plague population.
In fact, research published in February in the journal Proceedings of the National Academy of Sciences suggested that the plague did write itself into human genomes: The descendants of plague-affected populations share certain changes in some immune genes.
To test the idea, DeWitte analyzed bones from London cemeteries housed at the Museum of London's Centre for Human Bioarchaeology. She studied 464 skeletons from three burial grounds dating to the 11th and 12th centuries, before the plague. Another 133 skeletons came from a cemetery used after the Black Death, from the 14th into the 16th century.
These cemeteries provided a mix of people from different socioeconomic classes and ages.
The longevity boost seen after the plague could have come as a result of the plague weeding out the weak and frail, DeWitte said, or it could have been because of another plague side effect. With as much as half of the population dead, survivors in the post-plague era had more resources available to them. Historical documentation records an improvement in diet, especially among the poor, DeWitte said.
"They were eating more meat and fish and better-quality bread, and in greater quantities," she said.
Or the effect could be a combination of both natural selection and improved diet, DeWitte said. She's now starting a project to find out whether Europe's population was particularly unhealthy prior to the Black Death, and if health trends may have given the pestilence a foothold.
The Black Death was an emerging disease in the 14th century, DeWitte said, not unlike HIV or Ebola today. Understanding how human populations responded gives us more knowledge about how disease and humanity interact, she said. Y. pestis strains still cause bubonic plague today, though not at the pandemic levels seen in the Middle Ages.
"Diseases like the Black Death have the ability to powerfully shape human demography and human biology," DeWitte said.
Scientists sequence the full Black Death genome and find the mother of all plagues
The road of East Smithfield runs through east London and carries a deep legacy of death. Two cemeteries, established in the area in the 14th century, contain round 2,500 of bodies, piled five deep. These remains belong to people killed by the Black Death, an epidemic that killed between 30 and 50 percent of Europe in just five years. It was one of the biggest disasters in human history and seven centuries on, its victims are still telling its story.
In the latest chapters, Verena Schuenemann from the University of Tubingen and Kirsten Bos from McMaster University have used samples from East Smithfield to reconstruct the full genome of the bacterium behind the Black Death. This species – Yersinia pestis – still causes plague today, and the modern strains are surprisingly similar to the ancient one.
Compared to the strain that acts as a reference for modern plague, the ancient genome differs by only 97 DNA ‘letters’ out of around 4.6 million. Y.pestis may not be the same bacterium that butchered medieval Europe 660 years ago, but it’s not far off. Indeed, Schuenemann and Bos found that all of the strains that infect humans today descended from one that circulated during the Black Death. Even now, people are still succumbing to a dynasty of disease that began in the Dark Ages.
The Black Death is supposedly the second of a trilogy of plague pandemics. It came after the Plague of Justinian in the sixth to eighth centuries, and preceded modern plague, which infects some 2,000 people a year. But some scientists and historians saw features in the Black Death that separates it from other plague pandemics – it spread too quickly, killed too often, recurred too slowly, appeared in different seasons, caused symptoms in different parts of the body, and so on.
These differences have fuelled many alternative theories for the Black Death, which push Y.pestis out of the picture. Was it caused by an Ebola-like virus? An outbreak of anthrax? Some as-yet-unidentified infection that has since gone extinct? In 2000, Didier Raoult tried to solve the debate by sequencing DNA from the teeth of three Black Death victims, exhumed from a French grave. He found Y.pestis DNA. “We believe that we can end the controversy,” he wrote. “Medieval Black Death was plague.”
Raoult was half-wrong. The controversy did not end. Some people argued that it’s not clear if the remains came from Black Death victims at all. Meanwhile, Alan Cooper analysed teeth from 66 skeletons taken from so-called “plague pits”, including the one in East Smithfield. He found no trace of Y.pestisHe found no trace of Y.pestis. Other teams did their own analyses, and things went back and forth with a panto-like tempo. Oh yes, Y.pestis was thereOh yes, Y.pestis was thereOh yes, Y.pestis was there. Oh no it wasn’t. Oh yes it wasOh yes it was.
In 2010, Stephanie Haensch served up some of the strongest evidence that Y.pestis caused the Black Death, using DNA extracted from a variety of European burial sites. Schuenemann and Bos bolstered her conclusion by taking DNA from bodies that had been previously exhumed from East Smithfield, and stored in the Museum of London. “We sifted through every single intact skeleton and every intact tooth in the collection,” says Bos. They extracted DNA from 99 bones and teeth and found Y.pestis in 20 of them.
Schuenemann and Bos took great care to ensure that their sequences hadn’t been contaminated by modern bacteria. Aside from the usual precautions, they did all of her work at a facility that had never touched a Y.pestis sample, they had the results independently confirmed in a different lab, and they found traces of DNA damage that are characteristic of ancient sequences. They also failed to find any Y.pestis DNA in samples treated in exactly the same way, taken from a medieval cemetery that preceded the Black Death. Finally, it’s clear that the people exhumed from East Smithfield did indeed die from the Black Death – it’s one of the few places around the world that has been “definitively and uniquely” linked to that pandemic.
Even though they had its DNA, deciphering the ancient bacterium’s genome was difficult. The DNA was so heavily fractured that Schuenemann and Bos only managed to extract enough from four of their teeth. They lined up the fragments against a modern plague genome, and looked for overlaps between the remaining stragglers. In the draft that they’ve published, every stretch of DNA has been checked an average of 28 times.
By comparing this ancient genome with 17 modern ones, and those of other related bacteria, Scheuenemann and Bos created a family tree of plague that reveals the history of the disease. They showed that the last common ancestor of all modern plagues, lived between 1282 and 1343 before it swept through Europe, diversifying as it went. The East Smithfield strain was very close to that ancestral strain, differing by only two DNA letters.
This raises some questions about the plague of Justinian. The team think that it was either the work of an entirely different microbe, or it was caused by a strain of Y.pestis that is no longer around and likely left no descendants behind. It was the supposed second pandemic – the Black Death – that truly introduced Y.pestis to the world. This global tour seeded the strains that exist today.
By the time it hit East Smithfield, the plague was already changing. Schuenemann and Bos found that one of their four teeth harboured a slightly different version of Y.pestis, which was three DNA letters closer to modern strains than the other ancient ones. Even in the middle of the pandemic, the bacterium was mutating.
In the intervening centuries, Y.pestis has changed but not by much. None of the few differences between the ancient and modern genomes appear in genes that affect how good the bacterium is at causing diseases. None of them can obviously explain why the Black Death was so much more virulent than modern plague. “There’s no particular smoking gun,” says Hendrik Poinar, who was one of the study’s leaders.
That’s somewhat anticlimactic. In August, Poinar told me: “We need to know what changes in the ancient [bacterium] might have accounted for its tremendous virulence… There is really no way to know anything about the biology of the pathogen, until the entire genome is sequenced.” Now that the full genome is out, it seems to offer precious few clues.
Instead, the team thinks that a constellation of other factors might have made the Black Death such a potent pandemic. At the time, medieval Europe went through a drastic change in climate, becoming colder and wetter. Black rat numbers shot up, crops suffered and people went hungry. “It’s hard to believe that these people living in 1348 London weren’t being infected by various viruses,” says Poinar. “So you probably had an immune compromised population living in very stressful conditions, and they were hit by Y.pestis, maybe for the first time.” They were both physically and culturally unprepared. Their immune systems were naive, they didn’t know what the disease was, and they didn’t know how to treat or prevent it.
In later centuries, it was a different story. Medical treatments helped to cope with the symptoms and affected people were quickly quarantined. Today, we have antibiotics that help to treat plague, and these would be effective against the Black Death strain. We have evolved too. People who were most susceptible to plague were killed, which probably left the most resistant survivors behind. Next, Poinar wants to look at the DNA of people buried in pre-plague and post-plague cemeteries to see if the Black Death had altered our own genome.
Sequencing the Black Death genome may not tell us about why it was so deadly, but it still reveals how the bacterium evolved. Now, Schuenemann and Bos can look at how Y.pestis transformed from a bacterium that infects rodents to one that kills humans and how it evolved over time. That knowledge could be very important, especially since plague is rebounding as a “re-emerging” disease.
The Black Death strain is the second historical pathogen whose genome has been sequenced and certainly the oldest (the first was the 1918 pandemic flu). There are many others to look at, including the Justinian plague strain, and historical versions of tuberculosis, syphilis and cholera.
In the meantime, the East Smithfield bodies have told their story and Bos and Schuenemann are letting them rest. They were very careful with the teeth that they yanked DNA from, and they are now returning these samples to the Museum of London. Having yielded their secrets, they’ll be stuck back into their old skeletons.
Reference: Bos, Schuenemann, Golding, Burbano, Waglechner, Coombes, McPhee, DeWitte, Meyer, Schmedes, Wood, Earn, Herring, Bauer, Poinar & Kruase. 2011. A draft genome of Yersinia pestis from victims of the Black Death. Nature http://dx.doi.org/10.1038/nature10549
Schuenemann, Bos, deWitte, Schmedes, Jamieson, Mittnik, Forrest, Coombes, Wood, Earn, White, Krause & Poinar. 2011. Targeted enrichment of ancient pathogens yielding the pPCP1 plasmid of Yersinia pestis from victims of the Black Death. PNAS http://dx.doi.org/10.1073/pnas.1105107108
PS Oddly, the team’s new paper, where they publish the full Black Death genome, somewhat refutes their first one, where they had only sequenced fragments. Previously, they identified two mutations in the ancient DNA that weren’t seen in any other strain. But those two mutations aren’t there in the full genome, and it now seems that they were a mistake. Ancient DNA can be chemically damaged so that Cs change into Ts. That’s probably what happened in the previous study. Schuenemann and Bos are more confident that their new sequences are correct. They treated their samples with a method that repairs the C-to-T changes, and they went over every bit of DNA 30 times.
The Bubonic Plague resulted in long-term changes to human immunity
AURORA, Colo. — The Bubonic plague, or “Black Death,” wreaked havoc all over Europe for centuries during Medieval times. Interestingly, a new study finds that the awful disease left a lasting impression on humanity – and not just in the history books. Scientists from the University of Colorado have collected compelling evidence suggesting the plague sparked evolutionary, immune system changes in human DNA that remain to this day.
Researchers examined the remains of 36 bubonic plague victims buried in a 16th century mass grave in Germany to make these discoveries.
“We found that innate immune markers increased in frequency in modern people from the town compared to plague victims,” says the study’s joint-senior author Paul Norman, PhD, associate professor in the Division of Personalized Medicine at Colorado’s School of Medicine, in a university release. “This suggests these markers might have evolved to resist the plague.”
The team collected DNA from the inner ear bones of the remains, which had been residing in the southern German city of Ellwangen. This is worth noting because Ellwangen dealt with bubonic plague outbreaks in both the 16th and 17th centuries. In addition, study authors compared the DNA to samples from 50 modern residents of the area.
So how did the plague change in the human immune system?
Their analyses reveal modern residents have changes in their “allele distribution for two innate pattern-recognition receptors and four Human Leukocyte Antigen molecules.” These genes help the body trigger and and direct its immune response to an infection. Researchers believe exposure to Yersinia pestis, a pathogen that causes the bubonic plague, caused these changes to take place.
“We propose that these frequency changes could have resulted from Y.pestis plague exposure during the 16th century,” Norman adds.
This is the first study ever to suggest that Yersinia pestis caused long-term changes in immunity-relevant genes in Germany and probably many other European regions as well. Considering that the bubonic plague persisted across Europe for roughly 5,000 years, researchers speculate immunity genes could have been dormant in humans for a long time and only recently “activated” through epidemic events.
“Although the lethality of the plague is very high without treatment it remains likely that specific individuals are protected from, or more susceptible to, severe disease through polymorphism in the determinants of natural immunity,” researchers write. “In this case, any change in allele frequencies that occurred during a given epidemic crisis could be evident as genetic adaptation and detectable in modern day individuals.”
So does virus immunity still come down to survival of the fittest?
Additional simulations conducted by the team show that in all likelihood natural selection helped spark those allele frequency changes.
“I think this study shows that we can focus on these same families of genes in looking at immunity in modern pandemics,” Norman continues. “We know these genes were heavily involved in driving resistance to infections. It sheds light on our own evolution.”
“There will always be people who have some resistance. They just don’t get sick and die, and the human population bounces back. I wouldn’t want to discourage anyone from taking a vaccine for the current pandemic,” the study author concludes. “It’s a much safer bet than counting on your genes to save you.”
The study appears in the journal Molecular Biology and Evolution.
European writers contemporary with the plague described the disease in Latin as pestis or pestilentia, 'pestilence' epidemia, 'epidemic' mortalitas, 'mortality'.  In English prior to the 18th century, the event was called the "pestilence" or "great pestilence", "the plague" or the "great death".    Subsequent to the pandemic "the furste moreyn" (first murrain) or "first pestilence" was applied, to distinguish the mid-14th century phenomenon from other infectious diseases and epidemics of plague.  The 1347 pandemic plague was not referred to specifically as "black" in the 14th or 15th centuries in any European language, though the expression "black death" had occasionally been applied to fatal disease beforehand. 
"Black death" was not used to describe the plague pandemic in English until the 1750s the term is first attested in 1755, where it translated Danish: den sorte død, lit. 'the black death'.   This expression as a proper name for the pandemic had been popularized by Swedish and Danish chroniclers in the 15th and early 16th centuries, and in the 16th and 17th centuries was transferred to other languages as a calque: Icelandic: svarti dauði, German: der schwarze Tod, and French: la mort noire.   Previously, most European languages had named the pandemic a variant or calque of the Latin: magna mortalitas, lit. 'Great Death'. 
The phrase 'black death' – describing Death as black – is very old. Homer used it in the Odyssey to describe the monstrous Scylla, with her mouths "full of black Death" (Ancient Greek: πλεῖοι μέλανος Θανάτοιο , romanized: pleîoi mélanos Thanátoio).   Seneca the Younger may have been the first to describe an epidemic as 'black death', (Latin: mors atra) but only in reference to the acute lethality and dark prognosis of disease.    The 12th–13th century French physician Gilles de Corbeil had already used atra mors to refer to a "pestilential fever" (febris pestilentialis) in his work On the Signs and Symptoms of Diseases (De signis et symptomatibus aegritudium).   The phrase mors nigra, 'black death', was used in 1350 by Simon de Covino (or Couvin), a Belgian astronomer, in his poem "On the Judgement of the Sun at a Feast of Saturn" (De judicio Solis in convivio Saturni), which attributes the plague to an astrological conjunction of Jupiter and Saturn.  His use of the phrase is not connected unambiguously with the plague pandemic of 1347 and appears to refer to the fatal outcome of disease. 
The historian Cardinal Francis Aidan Gasquet wrote about the Great Pestilence in 1893  and suggested that it had been "some form of the ordinary Eastern or bubonic plague".  [c] In 1908, Gasquet claimed that use of the name atra mors for the 14th-century epidemic first appeared in a 1631 book on Danish history by J. I. Pontanus: "Commonly and from its effects, they called it the black death" (Vulgo & ab effectu atram mortem vocitabant).  
Recent research has suggested plague first infected humans in Europe and Asia in the Late Neolithic-Early Bronze Age.  Research in 2018 found evidence of Yersinia pestis in an ancient Swedish tomb, which may have been associated with the "Neolithic decline" around 3000 BCE, in which European populations fell significantly.   This Y. pestis may have been different from more modern types, with bubonic plague transmissible by fleas first known from Bronze Age remains near Samara. 
The symptoms of bubonic plague are first attested in a fragment of Rufus of Ephesus preserved by Oribasius these ancient medical authorities suggest bubonic plague had appeared in the Roman Empire before the reign of Trajan, six centuries before arriving at Pelusium in the reign of Justinian I.  In 2013, researchers confirmed earlier speculation that the cause of the Plague of Justinian (541–542 CE, with recurrences until 750) was Y. pestis.   This is known as the First plague pandemic.
The most authoritative contemporary account is found in a report from the medical faculty in Paris to Philip VI of France. It blamed the heavens, in the form of a conjunction of three planets in 1345 that caused a "great pestilence in the air" (miasma theory).  Muslim religious scholars taught that the pandemic was a “martyrdom and mercy” from God, assuring the believer's place in paradise. For non-believers, it was a punishment.  Some Muslim doctors cautioned against trying to prevent or treat a disease sent by God. Others adopted preventive measures and treatments for plague used by Europeans. These Muslim doctors also depended on the writings of the ancient Greeks.  
Predominant modern theory
Due to climate change in Asia, rodents began to flee the dried-out grasslands to more populated areas, spreading the disease.  The plague disease, caused by the bacterium Yersinia pestis, is enzootic (commonly present) in populations of fleas carried by ground rodents, including marmots, in various areas, including Central Asia, Kurdistan, Western Asia, North India, Uganda and the western United States.  
Y. pestis was discovered by Alexandre Yersin, a pupil of Louis Pasteur, during an epidemic of bubonic plague in Hong Kong in 1894 Yersin also proved this bacillus was present in rodents and suggested the rat was the main vehicle of transmission.   The mechanism by which Y. pestis is usually transmitted was established in 1898 by Paul-Louis Simond and was found to involve the bites of fleas whose midguts had become obstructed by replicating Y. pestis several days after feeding on an infected host. This blockage starves the fleas and drives them to aggressive feeding behaviour and attempts to clear the blockage by regurgitation, resulting in thousands of plague bacteria being flushed into the feeding site, infecting the host. The bubonic plague mechanism was also dependent on two populations of rodents: one resistant to the disease, which act as hosts, keeping the disease endemic, and a second that lack resistance. When the second population dies, the fleas move on to other hosts, including people, thus creating a human epidemic. 
Definitive confirmation of the role of Y. pestis arrived in 2010 with a publication in PLOS Pathogens by Haensch et al.  [d] They assessed the presence of DNA/RNA with polymerase chain reaction (PCR) techniques for Y. pestis from the tooth sockets in human skeletons from mass graves in northern, central and southern Europe that were associated archaeologically with the Black Death and subsequent resurgences. The authors concluded that this new research, together with prior analyses from the south of France and Germany, "ends the debate about the cause of the Black Death, and unambiguously demonstrates that Y. pestis was the causative agent of the epidemic plague that devastated Europe during the Middle Ages".  In 2011, these results were further confirmed with genetic evidence derived from Black Death victims in the East Smithfield burial site in England. Schuenemann et al. concluded in 2011 "that the Black Death in medieval Europe was caused by a variant of Y. pestis that may no longer exist". 
Later in 2011, Bos et al. reported in Nature the first draft genome of Y. pestis from plague victims from the same East Smithfield cemetery and indicated that the strain that caused the Black Death is ancestral to most modern strains of Y. pestis. 
Since this time, further genomic papers have further confirmed the phylogenetic placement of the Y. pestis strain responsible for the Black Death as both the ancestor  of later plague epidemics including the third plague pandemic and as the descendant  of the strain responsible for the Plague of Justinian. In addition, plague genomes from significantly earlier in prehistory have been recovered. 
DNA taken from 25 skeletons from 14th century London have shown plague is a strain of Y. pestis almost identical to that which hit Madagascar in 2013.  
It is recognised that an epidemiological account of plague is as important as an identification of symptoms, but researchers are hampered by the lack of reliable statistics from this period. Most work has been done on the spread of the disease in England, and even estimates of overall population at the start vary by over 100% as no census was undertaken in England between the time of publication of the Domesday Book of 1086 and the poll tax of the year 1377.  Estimates of plague victims are usually extrapolated from figures for the clergy.
Mathematical modelling is used to match the spreading patterns and the means of transmission. A research in 2018 challenged the popular hypothesis that "infected rats died, their flea parasites could have jumped from the recently dead rat hosts to humans". It suggested an alternative model in which "the disease was spread from human fleas and body lice to other people". The second model claims to better fit the trends of death toll because the rat-flea-human hypothesis would have produced a delayed but very high spike in deaths, which contradict historical death data.  
Lars Walløe complains that all of these authors "take it for granted that Simond's infection model, black rat → rat flea → human, which was developed to explain the spread of plague in India, is the only way an epidemic of Yersinia pestis infection could spread", whilst pointing to several other possibilities.  Similarly, Monica Green has argued that greater attention is needed to the range of (especially non-commensal) animals that might be involved in the transmission of plague. 
Archaeologist Barney Sloane has argued that there is insufficient evidence of the extinction of numerous rats in the archaeological record of the medieval waterfront in London and that the disease spread too quickly to support the thesis that Y. pestis was spread from fleas on rats he argues that transmission must have been person to person.   This theory is supported by research in 2018 which suggested transmission was more likely by body lice and fleas during the second plague pandemic. 
Although academic debate continues, no single alternative solution has achieved widespread acceptance.  Many scholars arguing for Y. pestis as the major agent of the pandemic suggest that its extent and symptoms can be explained by a combination of bubonic plague with other diseases, including typhus, smallpox and respiratory infections. In addition to the bubonic infection, others point to additional septicaemic (a type of "blood poisoning") and pneumonic (an airborne plague that attacks the lungs before the rest of the body) forms of plague, which lengthen the duration of outbreaks throughout the seasons and help account for its high mortality rate and additional recorded symptoms.  In 2014, Public Health England announced the results of an examination of 25 bodies exhumed in the Clerkenwell area of London, as well as of wills registered in London during the period, which supported the pneumonic hypothesis.  Currently, while osteoarcheologists have conclusively verified the presence of Y. pestis bacteria in burial sites across northern Europe through examination of bones and dental pulp, no other epidemic pathogen has been discovered to bolster the alternative explanations. In the words of one researcher: "Finally, plague is plague." 
The importance of hygiene was recognised only in the nineteenth century with the development of the germ theory of disease until then streets were commonly filthy, with live animals of all sorts around and human parasites abounding, facilitating the spread of transmissible disease. 
According to a team of medical geneticists led by Mark Achtman that analysed the genetic variation of the bacterium, Yersinia pestis "evolved in or near China",   from which it spread around the world in multiple epidemics. Later research by a team led by Galina Eroshenko places the origins more specifically in the Tian Shan mountains on the border between Kyrgyzstan and China. 
Nestorian graves dating to 1338–1339 near Issyk-Kul in Kyrgyzstan have inscriptions referring to plague, which has led some historians and epidemiologists to think they mark the outbreak of the epidemic. Others favour an origin in China.  According to this theory, the disease may have travelled along the Silk Road with Mongol armies and traders, or it could have arrived via ship.  Epidemics killed an estimated 25 million across Asia during the fifteen years before the Black Death reached Constantinople in 1347.  
Research on the Delhi Sultanate and the Yuan Dynasty shows no evidence of any serious epidemic in fourteenth-century India and no specific evidence of plague in fourteenth-century China, suggesting that the Black Death may not have reached these regions.    Ole Benedictow argues that since the first clear reports of the Black Death come from Kaffa, the Black Death most likely originated in the nearby plague focus on the northwestern shore of the Caspian Sea. 
. But at length it came to Gloucester, yea even to Oxford and to London, and finally it spread over all England and so wasted the people that scarce the tenth person of any sort was left alive.
Plague was reportedly first introduced to Europe via Genoese traders from their port city of Kaffa in the Crimea in 1347. During a protracted siege of the city, in 1345–1346 the Mongol Golden Horde army of Jani Beg, whose mainly Tatar troops were suffering from the disease, catapulted infected corpses over the city walls of Kaffa to infect the inhabitants,  though it is more likely that infected rats travelled across the siege lines to spread the epidemic to the inhabitants.   As the disease took hold, Genoese traders fled across the Black Sea to Constantinople, where the disease first arrived in Europe in summer 1347. 
The epidemic there killed the 13-year-old son of the Byzantine emperor, John VI Kantakouzenos, who wrote a description of the disease modelled on Thucydides's account of the 5th century BCE Plague of Athens, but noting the spread of the Black Death by ship between maritime cities.  Nicephorus Gregoras also described in writing to Demetrios Kydones the rising death toll, the futility of medicine, and the panic of the citizens.  The first outbreak in Constantinople lasted a year, but the disease recurred ten times before 1400. 
Carried by twelve Genoese galleys, plague arrived by ship in Sicily in October 1347  the disease spread rapidly all over the island. Galleys from Kaffa reached Genoa and Venice in January 1348, but it was the outbreak in Pisa a few weeks later that was the entry point to northern Italy. Towards the end of January, one of the galleys expelled from Italy arrived in Marseilles. 
From Italy, the disease spread northwest across Europe, striking France, Spain (the epidemic began to wreak havoc first on the Crown of Aragon in the spring of 1348),  Portugal and England by June 1348, then spread east and north through Germany, Scotland and Scandinavia from 1348 to 1350. It was introduced into Norway in 1349 when a ship landed at Askøy, then spread to Bjørgvin (modern Bergen) and Iceland.  Finally, it spread to northwestern Russia in 1351. Plague was somewhat more uncommon in parts of Europe with less developed trade with their neighbours, including the majority of the Basque Country, isolated parts of Belgium and the Netherlands, and isolated Alpine villages throughout the continent.   
According to some epidemiologists, periods of unfavourable weather decimated plague-infected rodent populations and forced their fleas onto alternative hosts,  inducing plague outbreaks which often peaked in the hot summers of the Mediterranean,  as well as during the cool autumn months of the southern Baltic states.  [e] Among many other culprits of plague contagiousness, malnutrition, even if distantly, also contributed to such an immense loss in European population, since it weakened immune systems. 
Western Asian and North African outbreak
The disease struck various regions in the Middle East and North Africa during the pandemic, leading to serious depopulation and permanent change in both economic and social structures.  As infected rodents infected new rodents, the disease spread across the region, entering also from southern Russia.
By autumn 1347, plague had reached Alexandria in Egypt, transmitted by sea from Constantinople according to a contemporary witness, from a single merchant ship carrying slaves.  By late summer 1348 it reached Cairo, capital of the Mamluk Sultanate, cultural centre of the Islamic world, and the largest city in the Mediterranean Basin the Bahriyya child sultan an-Nasir Hasan fled and more than a third of the 600,000 residents died.  The Nile was choked with corpses despite Cairo having a medieval hospital, the late 13th century bimaristan of the Qalawun complex.  The historian al-Maqrizi described the abundant work for grave-diggers and practitioners of funeral rites, and plague recurred in Cairo more than fifty times over the following century and half. 
During 1347, the disease travelled eastward to Gaza by April by July it had reached Damascus, and in October plague had broken out in Aleppo.  That year, in the territory of modern Lebanon, Syria, Israel, and Palestine, the cities of Ashkelon, Acre, Jerusalem, Sidon, and Homs were all infected. In 1348–1349, the disease reached Antioch. The city's residents fled to the north, but most of them ended up dying during the journey.  Within two years, the plague had spread throughout the Islamic world, from Arabia across North Africa.  [ page needed ] The pandemic spread westwards from Alexandria along the African coast, while in April 1348 Tunis was infected by ship from Sicily. Tunis was then under attack by an army from Morocco this army dispersed in 1348 and brought the contagion with them to Morocco, whose epidemic may also have been seeded from the Islamic city of Almería in al-Andalus. 
Mecca became infected in 1348 by pilgrims performing the Hajj.  In 1351 or 1352, the Rasulid sultan of the Yemen, al-Mujahid Ali, was released from Mamluk captivity in Egypt and carried plague with him on his return home.   During 1348, records show the city of Mosul suffered a massive epidemic, and the city of Baghdad experienced a second round of the disease. [ citation needed ]
Signs and symptoms
Symptoms of the disease include fever of 38–41 °C (100–106 °F), headaches, painful aching joints, nausea and vomiting, and a general feeling of malaise. Left untreated, of those that contract the bubonic plague, 80 percent die within eight days. 
Contemporary accounts of the pandemic are varied and often imprecise. The most commonly noted symptom was the appearance of buboes (or gavocciolos) in the groin, neck, and armpits, which oozed pus and bled when opened.  Boccaccio's description:
In men and women alike it first betrayed itself by the emergence of certain tumours in the groin or armpits, some of which grew as large as a common apple, others as an egg . From the two said parts of the body this deadly gavocciolo soon began to propagate and spread itself in all directions indifferently after which the form of the malady began to change, black spots or livid making their appearance in many cases on the arm or the thigh or elsewhere, now few and large, now minute and numerous. As the gavocciolo had been and still was an infallible token of approaching death, such also were these spots on whomsoever they showed themselves.   [f]
This was followed by acute fever and vomiting of blood. Most victims died two to seven days after initial infection. Freckle-like spots and rashes,  which could have been caused by flea-bites, were identified as another potential sign of plague.
Lodewijk Heyligen, whose master the Cardinal Colonna died of plague in 1348, noted a distinct form of the disease, pneumonic plague, that infected the lungs and led to respiratory problems.  Symptoms include fever, cough, and blood-tinged sputum. As the disease progresses, sputum becomes free-flowing and bright red. Pneumonic plague has a mortality rate of 90 to 95 percent. 
Septicaemic plague is the least common of the three forms, with a mortality rate near 100%. Symptoms are high fevers and purple skin patches (purpura due to disseminated intravascular coagulation).  In cases of pneumonic and particularly septicaemic plague, the progress of the disease is so rapid that there would often be no time for the development of the enlarged lymph nodes that were noted as buboes. 
There are no exact figures for the death toll the rate varied widely by locality. In urban centres, the greater the population before the outbreak, the longer the duration of the period of abnormal mortality.  It killed some 75 to 200 million people in Eurasia.    [ better source needed ] The mortality rate of the Black Death in the 14th century was far greater than the worst 20th-century outbreaks of Y. pestis plague, which occurred in India and killed as much as 3% of the population of certain cities.  The overwhelming number of deceased bodies produced by the Black Death caused the necessity of mass burial sites in Europe, sometimes including up to several hundred or several thousand skeletons.  The mass burial sites that have been excavated have allowed archaeologists to continue interpreting and defining the biological, sociological, historical, and anthropological implications of the Black Death. 
According to medieval historian Philip Daileader, it is likely that over four years, 45–50% of the European population died of plague.  [g] Norwegian historian Ole Benedictow suggests it could have been as much as 60% of the European population.  [h] In 1348, the disease spread so rapidly that before any physicians or government authorities had time to reflect upon its origins, about a third of the European population had already perished. In crowded cities, it was not uncommon for as much as 50% of the population to die.  Half of Paris' population of 100,000 people died. In Italy, the population of Florence was reduced from between 110,000 and 120,000 inhabitants in 1338 down to 50,000 in 1351. At least 60% of the population of Hamburg and Bremen perished,  and a similar percentage of Londoners may have died from the disease as well,  with a death toll of approximately 62,000 between 1346 and 1353.  [i] Florence's tax records suggest that 80% of the city's population died within four months in 1348.  Before 1350, there were about 170,000 settlements in Germany, and this was reduced by nearly 40,000 by 1450.  The disease bypassed some areas, with the most isolated areas being less vulnerable to contagion. Plague did not appear in Douai in Flanders until the turn of the 15th century, and the impact was less severe on the populations of Hainaut, Finland, northern Germany, and areas of Poland.  Monks, nuns, and priests were especially hard-hit since they cared for victims of the Black Death. 
The physician to the Avignon Papacy, Raimundo Chalmel de Vinario (Latin: Magister Raimundus, lit. 'Master Raymond'), observed the decreasing mortality rate of successive outbreaks of plague in 1347–48, 1362, 1371, and 1382 in his 1382 treatise On Epidemics (De epidemica).  In the first outbreak, two thirds of the population contracted the illness and most patients died in the next, half the population became ill but only some died by the third, a tenth were affected and many survived while by the fourth occurrence, only one in twenty people were sickened and most of them survived.  By the 1380s in Europe, it predominantly affected children.  Chalmel de Vinario recognized that bloodletting was ineffective (though he continued to prescribe bleeding for members of the Roman Curia, whom he disliked), and claimed that all true cases of plague were caused by astrological factors and were incurable he himself was never able to effect a cure. 
The most widely accepted estimate for the Middle East, including Iraq, Iran, and Syria, during this time, is for a death toll of about a third of the population.  The Black Death killed about 40% of Egypt's population.  In Cairo, with a population numbering as many as 600,000, and possibly the largest city west of China, between one third and 40% of the inhabitants died inside of eight months. 
Italian chronicler Agnolo di Tura recorded his experience from Siena, where plague arrived in May 1348:
Father abandoned child, wife husband, one brother another for this illness seemed to strike through the breath and sight. And so they died. And none could be found to bury the dead for money or friendship. Members of a household brought their dead to a ditch as best they could, without priest, without divine offices . great pits were dug and piled deep with the multitude of dead. And they died by the hundreds both day and night . And as soon as those ditches were filled more were dug . And I, Agnolo di Tura . buried my five children with my own hands. And there were also those who were so sparsely covered with earth that the dogs dragged them forth and devoured many bodies throughout the city. There was no one who wept for any death, for all awaited death. And so many died that all believed it was the end of the world. 
With such a large population decline from the pandemic, wages soared in response to a labour shortage.  On the other hand, in the quarter century after the Black Death in England, it is clear many labourers, artisans, and craftsmen, those living from money-wages alone, did suffer a reduction in real incomes owing to rampant inflation.  Landowners were also pushed to substitute monetary rents for labour services in an effort to keep tenants. 
Some historians believe the innumerable deaths brought on by the pandemic cooled the climate by freeing up land and triggering reforestation. This may have led to the Little Ice Age. 
Renewed religious fervour and fanaticism bloomed in the wake of the Black Death. Some Europeans targeted "various groups such as Jews, friars, foreigners, beggars, pilgrims", lepers,   and Romani, blaming them for the crisis. Lepers, and others with skin diseases such as acne or psoriasis, were killed throughout Europe.
Because 14th-century healers and governments were at a loss to explain or stop the disease, Europeans turned to astrological forces, earthquakes, and the poisoning of wells by Jews as possible reasons for outbreaks.  Many believed the epidemic was a punishment by God for their sins, and could be relieved by winning God's forgiveness. 
There were many attacks against Jewish communities.  In the Strasbourg massacre of February 1349, about 2,000 Jews were murdered.  In August 1349, the Jewish communities in Mainz and Cologne were annihilated. By 1351, 60 major and 150 smaller Jewish communities had been destroyed.  During this period many Jews relocated to Poland, where they received a warm welcome from King Casimir the Great. 
One theory that has been advanced is that the devastation in Florence caused by the Black Death, which hit Europe between 1348 and 1350, resulted in a shift in the world view of people in 14th-century Italy and led to the Renaissance. Italy was particularly badly hit by the pandemic, and it has been speculated that the resulting familiarity with death caused thinkers to dwell more on their lives on Earth, rather than on spirituality and the afterlife.  [j] It has also been argued that the Black Death prompted a new wave of piety, manifested in the sponsorship of religious works of art. 
This does not fully explain why the Renaissance occurred in Italy in the 14th century. The Black Death was a pandemic that affected all of Europe in the ways described, not only Italy. The Renaissance's emergence in Italy was most likely the result of the complex interaction of the above factors,  in combination with an influx of Greek scholars following the fall of the Byzantine Empire. [ citation needed ] As a result of the drastic reduction in the populace the value of the working class increased, and commoners came to enjoy more freedom. To answer the increased need for labour, workers travelled in search of the most favorable position economically.  [ better source needed ]
Prior to the emergence of the Black Death, the workings of Europe were run by the Catholic Church and the continent was considered a feudalistic society, composed of fiefs and city-states.  The pandemic completely restructured both religion and political forces survivors began to turn to other forms of spirituality and the power dynamics of the fiefs and city-states crumbled.  
Cairo's population, partly owing to the numerous plague epidemics, was in the early 18th century half of what it was in 1347.  The populations of some Italian cities, notably Florence, did not regain their pre-14th century size until the 19th century.  The demographic decline due to the pandemic had economic consequences: the prices of food dropped and land values declined by 30–40% in most parts of Europe between 1350 and 1400.  Landholders faced a great loss, but for ordinary men and women it was a windfall. The survivors of the pandemic found not only that the prices of food were lower but also that lands were more abundant, and many of them inherited property from their dead relatives, and this probably destabilized feudalism.  
The word "quarantine" has its roots in this period, though the concept of isolating people to prevent the spread of disease is older. In the city-state of Ragusa (modern Dubrovnik, Croatia), a thirty-day isolation period was implemented in 1377 for new arrivals to the city from plague-affected areas. The isolation period was later extended to forty days, and given the name "quarantino" from the Italian word for "forty". 
Second plague pandemic
The plague repeatedly returned to haunt Europe and the Mediterranean throughout the 14th to 17th centuries.  According to Jean-Noël Biraben, the plague was present somewhere in Europe in every year between 1346 and 1671.  (Note that some researchers have cautions about the uncritical use of Biraben's data.  ) The second pandemic was particularly widespread in the following years: 1360–63 1374 1400 1438–39 1456–57 1464–66 1481–85 1500–03 1518–31 1544–48 1563–66 1573–88 1596–99 1602–11 1623–40 1644–54 and 1664–67. Subsequent outbreaks, though severe, marked the retreat from most of Europe (18th century) and northern Africa (19th century).  The historian George Sussman argued that the plague had not occurred in East Africa until the 1900s.  However, other sources suggest that the Second pandemic did indeed reach Sub-Saharan Africa. 
According to historian Geoffrey Parker, "France alone lost almost a million people to the plague in the epidemic of 1628–31."  In the first half of the 17th century, a plague claimed some 1.7 million victims in Italy.  More than 1.25 million deaths resulted from the extreme incidence of plague in 17th-century Spain. 
The Black Death ravaged much of the Islamic world.  Plague was present in at least one location in the Islamic world virtually every year between 1500 and 1850.  Plague repeatedly struck the cities of North Africa. Algiers lost 30,000–50,000 inhabitants to it in 1620–21, and again in 1654–57, 1665, 1691, and 1740–42.  Cairo suffered more than fifty plague epidemics within 150 years from the plague's first appearance, with the final outbreak of the second pandemic there in the 1840s.  Plague remained a major event in Ottoman society until the second quarter of the 19th century. Between 1701 and 1750, thirty-seven larger and smaller epidemics were recorded in Constantinople, and an additional thirty-one between 1751 and 1800.  Baghdad has suffered severely from visitations of the plague, and sometimes two-thirds of its population has been wiped out. 
Third plague pandemic
The third plague pandemic (1855–1859) started in China in the mid-19th century, spreading to all inhabited continents and killing 10 million people in India alone.  The investigation of the pathogen that caused the 19th-century plague was begun by teams of scientists who visited Hong Kong in 1894, among whom was the French-Swiss bacteriologist Alexandre Yersin, after whom the pathogen was named. 
Twelve plague outbreaks in Australia between 1900 and 1925 resulted in well over 1,000 deaths, chiefly in Sydney. This led to the establishment of a Public Health Department there which undertook some leading-edge research on plague transmission from rat fleas to humans via the bacillus Yersinia pestis. 
The first North American plague epidemic was the San Francisco plague of 1900–1904, followed by another outbreak in 1907–1908.   
Modern treatment methods include insecticides, the use of antibiotics, and a plague vaccine. It is feared that the plague bacterium could develop drug resistance and again become a major health threat. One case of a drug-resistant form of the bacterium was found in Madagascar in 1995.  A further outbreak in Madagascar was reported in November 2014.  In October 2017 the deadliest outbreak of the plague in modern times hit Madagascar, killing 170 people and infecting thousands. 
An estimate of the case fatality rate for the modern bubonic plague, following the introduction of antibiotics, is 11%, although it may be higher in underdeveloped regions. 
- A Journal of the Plague Year – 1722 book by Daniel Defoe describing the Great Plague of London of 1665–1666 – a 2010 action horror film set in medieval England in 1348 ("The Betrothed") – a plague novel by Alessandro Manzoni, set in Milan, and published in 1827 turned into an opera by Amilcare Ponchielli in 1856, and adapted for film in 1908, 1941, 1990, and 2004
- Cronaca fiorentina ("Chronicle of Florence") – a literary history of the plague, and of Florence up to 1386, by Baldassarre Bonaiuti
- Danse Macabre ("Dance of Death") – an artistic genre of allegory of the Late Middle Ages on the universality of death
- The Decameron – by Giovanni Boccaccio, finished in 1353. Tales told by a group of people sheltering from the Black Death in Florence. Numerous adaptations to other media have been made – a 1992 science fiction novel by Connie Willis
- A Feast in Time of Plague – a verse play by Aleksandr Pushkin (1830), made into an opera by César Cui in 1900 – a popular French legend supposed to provide immunity to the plague – Medieval "flagellant songs"
- "A Litany in Time of Plague" – a sonnet by Thomas Nashe which was part of his play Summer's Last Will and Testament (1592)
- The Plague – a 1947 novel by Albert Camus, often read as an allegory about Fascism
- The Seventh Seal – a 1957 film written and directed by Ingmar Bergman
- World Without End – a 2007 novel by Ken Follett, turned into a miniseries of the same name in 2012
- The Years of Rice and Salt – an alternative history novel by Kim Stanley Robinson set in a world in which the plague killed virtually all Europeans
- ^ Other names include Great Mortality (Latin: magna mortalitas, lit.'Great Death', common in the 14th century), atra mors, 'black death', the Great Plague, the Great Bubonic Plague or the Black Plague.
- ^ Declining temperatures following the end of the Medieval Warm Period added to the crisis
- ^ He was able to adopt the epidemiology of the bubonic plague for the Black Death for the second edition in 1908, implicating rats and fleas in the process, and his interpretation was widely accepted for other ancient and medieval epidemics, such as the Plague of Justinian that was prevalent in the Eastern Roman Empire from 541 to 700 CE. 
- ^ In 1998, Drancourt et al. reported the detection of Y. pestis DNA in human dental pulp from a medieval grave.  Another team led by Tom Gilbert cast doubt on this identification  and the techniques employed, stating that this method "does not allow us to confirm the identification of Y. pestis as the aetiological agent of the Black Death and subsequent plagues. In addition, the utility of the published tooth-based ancient DNA technique used to diagnose fatal bacteraemias in historical epidemics still awaits independent corroboration".
- ^ However, other researchers do not think that plague ever became endemic in Europe or its rat population. The disease repeatedly wiped out the rodent carriers, so that the fleas died out until a new outbreak from Central Asia repeated the process. The outbreaks have been shown to occur roughly 15 years after a warmer and wetter period in areas where plague is endemic in other species, such as gerbils. 
- ^ The only medical detail that is questionable in Boccaccio's description is that the gavocciolo was an "infallible token of approaching death", as, if the bubo discharges, recovery is possible. 
- ^ According to medieval historian Philip Daileader,
The trend of recent research is pointing to a figure more like 45–50% of the European population dying during a four-year period. There is a fair amount of geographic variation. In Mediterranean Europe, areas such as Italy, the south of France and Spain, where plague ran for about four years consecutively, it was probably closer to 75–80% of the population. In Germany and England . it was probably closer to 20%. 
Detailed study of the mortality data available points to two conspicuous features in relation to the mortality caused by the Black Death: namely the extreme level of mortality caused by the Black Death, and the remarkable similarity or consistency of the level of mortality, from Spain in southern Europe to England in north-western Europe. The data is sufficiently widespread and numerous to make it likely that the Black Death swept away around 60% of Europe's population. The generally assumed population of Europe at the time is about 80 million, implying that around 50 million people died in the Black Death. 
How to Prevent a Future Pandemic?
Plague and cholera pandemics first disseminated along trade and military routes. Thereafter, the geographical spread of pathogens followed the movement of human population through rail, ship and air travels. Nowadays, the globalization of travels and trade of animals and animal-based foods further increase the spread of infectious diseases and the speed with which they are disseminated around the world. Land use and urbanization to accommodate agriculture and living areas modify the habitats of pathogens, hosts and disease vectors and affect the transmission dynamics of infections to humans. The geographic distribution of disease vectors and hosts as well as the living habitats of microorganisms is also affected by climate changes and could potentially increase the spread of pathogens. Increased contacts between humans and animals through breeding, hunting, wet markets and trade of exotic pets also favor the risk of spillover of zoonotic pathogens. The spread of infectious diseases is thus expected to increase due to human activities and their effects on the environment. Epidemics and pandemics will also occur more frequently and will represent new challenges for public health.
In order to control the transmission of water-borne pathogens such as V. cholera, the WHO has launched a water, sanitation and hygiene (WASH) program in developing countries (Matilla et al., 2018). This program emphasizes the provision of safe and clean sources of water, effective sanitation infrastructure and ensures appropriate hygiene practices. The WASH program was reported to increase safe drinking water accesses, safe sanitation services and basic handwashing facilities with soap and water at home to 71%, 45% and 60% of the global population, respectively (UNICEF and World Health Organization [WHO], 2019).
Vector control is the primary tool to control vector-borne diseases such as malaria, Dengue virus, Chikungunya virus and Zika virus (Wilson A.L. et al., 2020). These methods can target either the immature stages (by the use of predator species and chemical or biological larvicides or by the modification of the habitat) or the adult vectors (by the use of nets, topical repellents, insecticides and spraying). Furthermore, novel vector control methods are under development such as the genetic manipulation of mosquitos (Hammond and Galizi, 2017), bacterial infection of vectors (e.g., Wolbachia) (Flores and O’Neill, 2018) and eave tubes with insecticide-laden electrostatic netting (Knols et al., 2016). However, the development of novel vector control tools is still needed.
The implementation of global surveillance programs for the rapid detection of pathogen spillover from animal to the human population is of prime importance. The One Health concept promotes optimal health for human, animal and environment (One Health Commission [OHC], 2020). The environmental effects resulting from land use, urbanization and climate changes may increase the risk of pathogens spillover from animals to humans and emphasize the importance of a One Health integrative approach for the surveillance of zoonosis (Okello et al., 2011 Rabozzi et al., 2012). Such integrative approaches are used to implement surveillance programs for the prevention and control of emerging and re-emerging infections in developing countries. These multidisciplinary efforts could have positive impacts in these countries as they are the most afflicted by the effects of zoonoses (Bidaisee and Macpherson, 2014).
Viral zoonoses constitute particularly a serious threat to public health as viruses were at the origin of the most recent pandemics. It is thus important to evaluate the risk of cross-species transmission of viruses to humans. The viral richness associated to an animal species could predict zoonotic potential of mammalian viruses (Olival et al., 2017). It was shown that the cross-species transmission of mammalian viruses increases with respect to the phylogenetic proximity between hosts and humans. Furthermore, viruses that infect a phylogenetically broader ranges of hosts are more likely to be zoonotic. Characterizing the diversity of viruses in key wildlife species will help to reduce the time between detection and response during an outbreak (Epstein and Anthony, 2017). Furthermore, the global virome project was launched to detect and identify viral threats to human health, characterize the host ranges of viruses, identify behaviors that favor spillover, establish a global surveillance network and identify transmission and pathogenicity markers for high-risk viruses (Carroll et al., 2018 Kwok et al., 2020). Viral metagenomic next-generation sequencing analysis of nasal/throat swabs from individuals at risk of zoonotic infections was also used to expand the detection of novel viruses and the characterization of the respiratory virome of humans exposed to animals (Thi Kha Tu et al., 2020).
Strains of ‘Yersinia pestis’ were found on ancient human fossils
A new DNA study performed on Bronze Age human skeletons has revealed that the plague, well known for the Black Death in 1347, had first spread as early as the year 3,000 B.C. The investigation was published in the journal Cell Press.
The Black Death, caused by the bacteria Yersinia pestis, killed about 50 million people in Europe. The oldest evidence found of this bacteria was only about 1,500 years old even though scientists had already though it was responsible for early plagues as well.
Descriptions of the disease were also found which described its quick spread and some of the same symptoms that match modern outbreaks. Even though earlier outbreaks probably did not spread as fast as the Black Death, investigators believe it may have caused mass migrations in Europe and Asia.
The Black Death was one of the most devastating pandemics in human history, resulting in the deaths of an estimated 75 to 200 million people and peaking in Europe in the years 1346–53. Credit: Wikipedia
Scientists also consider that the Y-pestis was responsible for the Plague of Athens, dated back to the fifth century BC but real records of plague infections come from the Plague of Justinian, which occurred in the sixth century. Another example is the Great plague, one of the most devastating pandemics in recorded history.
During this new study, researchers analyzed the teeth samples from the remains of 101 ancient plague victims. These skeletons had been collected from a variety of archaeological excavations. Molecules of the Yersinia pestis were found in the DNA of seven individuals. The earliest body containing this bacteria dated back to the Bronze Age Siberia which dated to 2794 B.C.
Simon Rasmussen, a lead author of the study and a bioinformatician at the Technical University of Denmark said “We were able to find genuine Yersinia pestis DNA in our samples 3,000 years earlier than what had previously been shown,” as Live Science reported.
CDC (data from WHO). Credit: Business Insider
Investigators have also found that the bacteria has mutated over time. One of the genes that was not found in genomes from the Bronze Age was the ‘ymt gene’. More recent genomes are stronger and contain this gene, which protects the bacteria inside the guts of fleas and helps the insects spread the plague to humans.
Investigators believe this new advance may help them prevent and cure future plagues. “By knowing which new genes and mutations lead to the development of plague, we may be better at predicting or identifying bacteria that could develop into new infectious diseases” Rasmussen concluded.
BLACK DEATH SPREAD BY airborne and had TO BE by coughs and sneezes
BLACK DEATH SPREAD BY airborne and had TO BE by coughs and sneezes
It has long been thought the Black Death, the plague that decimated the population of Britain in the mid-14th century, was spread by fleas carried on rats.
However, 25 skeletons recently unearthed in Clerkenwell, London, believed to be of plague victims, have cast doubt on this age-old theory and provided evidence that they deadly disease may have, in fact, been airborne.
The DNA of the remains was compared to samples from an outbreak in Madagascar, in 2012, which killed 60 people.
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New theory: Analysis of skeletons discovered in London believed to be victims of the Black Death suggests the disease was not spread by rat fleas, but was in fact airborne
DNA of plague bacteria taken from the 25 skeletons discovered in Clerkenwell was compared to samples from a recent outbreak in Madagascar which killed 60 people
The remains were discovered during excavations of Charterhouse Square in Farringdon, London, an area of the capital left largely undisturbed for years
The scientists were shocked to discover that the two samples were an almost perfect match, meaning the 14th century plague was no more virulent than it is today.
They believe that for such a disease to have spread so quickly and cause so much damage it must have been spread by coughs and sneezes, getting into the lungs of its already weak and malnourished victims.
Dr Tim Brooks from Public Health England in Porton Down where the research was carried out, told the Guardian: 'As an explanation [rat fleas] for the Black Death in its own right, it simply isn't good enough. 'It cannot spread fast enough from one household to the next to cause the huge number of cases that we saw during the Black Death epidemics.'
It means that rather than being a bubonic plague it was in fact pneumonic meaning it was spread from human to human, rather than by flea bites.
The skeletons of 13 men, three women and two children, as well as seven other unidentifiable remains, were found under Charterhouse Square in Farringdon during excavation work for the 㾺.8 billion Crossrail project.
The DNA samples, which were extracted from the molar teeth of the skeletons, have also revealed intriguing details about the individual victims.
The researchers were shocked to discover that the two samples were an almost perfect match, meaning the 14th century plague was no more virulent than it is today
The DNA samples, which were extracted from the molar teeth of the skeletons, have also revealed intriguing details of the victims' lives
Don Walker, an osteologist with the Museum of London with one of the 25 skeletons found by construction workers under central London's Charterhouse Square last year
Researchers found that four in 10 Londoners killed during the epidemic grew up in other parts of Britain, making the medieval residents of London just as cosmopolitan as they are today.
Experts said the discovery of the skeletons was 'significant', saying that thousands more bodies could have been laid to rest in a mass grave in the area - which at the time was outside of the city boundaries.
Don Walker, an osteologist with the Museum of London, outlined the biography of one man whose ancient bones were found by construction workers under London's Charterhouse Square.
He was breast-fed as a baby, moved to London from another part of England, had bad tooth decay in childhood, grew up to work as a laborer, and died in early adulthood from the bubonic plague that ravaged Europe in the 14th century.
The poor man's life was nasty, brutish and short, but his afterlife is long and illuminating.
'It's fantastic we can look in such detail at an individual who died 600 years ago,' Walker said. 'It's incredible, really.'
Radiocarbon dating and analysis of pottery shards helped determine when the burials took place. Forensic geophysics - more commonly used in murder and war-crimes investigations - helped locate more graves under the square. Studying oxygen and strontium isotopes in the bones revealed details of diet and health.
Archaeologists were surprised to discover that the skeletons lay in layers and appeared to come from three different periods: the original Black Death epidemic in 1348-1350, and later outbreaks in 1361 and the early 15th century.
'It suggests that the burial ground was used again and again for the burial of plague victims,' said Jay Carver, Crossrail's lead archaeologist.
Bring out your dead: The Black Death decimated the population of Britain in the mid 14th century killing an estimated six of 10 londoners
The new finding have come from comparing DNA from teeth of the skeletons to samples from a recent plague outbreak in Madagascar
The excavation work was being carried out in order to make way for the new Crossrail train line
The Black Death is thought to have killed at least 75 million people, including half of Britain's population, yet the burials suggest a surprisingly high degree of social order - at first.
As the plague ravaged continental Europe, city fathers leased land for an emergency burial ground. The burials were simple but orderly, the bodies wrapped in shrouds and laid out in neat rows, sealed with a layer of clay.
The later skeletons, however, show more signs of upper-body injuries, consistent with a period of lawlessness and social breakdown.
Many of the bodies showed signs of poor health, the experts said. A high rate of back damage also suggested they had jobs involving heavy manual labour.
The remains also revealed that one of the bodies could have been that of a monk - after showing signs of vegetarianism in later life, which is something a Carthusian monk would have done during the 14th century.
One of the skeletons showed evidence of malnutrition and a large variation of diet 30 years prior to death, coinciding with the Great Famine of 1315 to 1317.
Six out of 10 sets of remains analysed were from people born and bred in London. But four had moved from further afield - presumably seeking work - from the southeast of England, central England or the east of England and one from northern England or Scotland.
Mr Carver said: 'This is probably the first time in modern archaeological investigation that we have finally found evidence for a burial ground in this area which potentially contains thousands of victims from the Black Death and potentially later plague events as well.
'Historical documents suggest the burial ground was established for poor strangers. There is no doubt from the osteological work that the individuals buried here were not the wealthy classes, and they are representing the typical Londoner.'
Six out of 10 bodies analysed were born and bred in London. But four had come from further afield - presumably seeking work - from the South East of England, central England or the East of England and one from northern England or Scotland
The remains also revealed that one of the bodies could have been that of a monk - after showing signs of vegetarianism in later life, which is something a Carthusian monk would have done during the 14th century
Archaeologist Jay Carver said: 'Analysis of the Crossrail find has revealed an extraordinary amount of information allowing us to solve a 660-year mystery'
He added: 'Analysis of the Crossrail find has revealed an extraordinary amount of information allowing us to solve a 660-year mystery. This discovery is a hugely important step forward in documenting and understanding Europe's most devastating pandemic.'
Forensic geophysics techniques have shown that there are potentially more burials across Charterhouse Square.
In July this year a 'community excavation project' will take place to try to determine the extent of the cemetery.
A similar skeleton formation was found in a Black Death burial site in nearby east Smithfield in the 1980s. Experts are now planning to compare the data gathered from the two burial sites.
The findings will be featured in a new Channel 4 programme, Return Of The Black Death, which will be aired at 8pm on April 6.
Crossrail's lead archeologist Jay Carver inspecting one of the 25 skeletons, left. Research has shown that the burial ground was established in 1348