DNA from ancient plague points to modern peril 
 
 By Richard Ingham (AFP) – Jan 27, 2014 
 
 Paris — "In some cases death came immediately; in others, after many days," the historian Procopius wrote as a terrifying disease scythed through Constantinople in 542 AD. 
 
 "With some, the body broke out with black pustules about as large as a lentil and these did not survive even one day, but all succumbed immediately. Vomiting of blood ensued in many, without visible cause, and immediately brought death." 
 
 What Procopius observed first hand was the Plague of Justinian, named after the Eastern Roman emperor he served and who contracted the disease but survived. 
 
 The first of three plague pandemics to have ravaged humanity, it killed between 25 and 100 million people across Asia, North Africa and Europe. 
 
 After an initial two-year rampage, it returned in waves before mysteriously disappearing in the middle of the eighth century. 
 
 Using DNA teased from 1,500-year-old teeth of plague victims buried in Germany, scientists have reconstructed the genetic profile of the killer and say its ability to mutate is a warning for people today. 
 
 Different from the Black Death 
 
 The strain of Yersinia pestis germ which caused the Plague of Justinian was different from the strain that triggered the Black Death in the 14th century, killing an estimated 30 million Europeans, they found. 
 
 It is also distinct from the Y. pestis strain that caused a third outbreak of plague in the late 19th century, and which was likely to have been a genetic offshoot from the Black Death microbe. 
 
 The evidence confirms, as expected, the role of rats as the germ's "reservoir" or natural source, according to a paper published in the journal The Lancet Infectious Diseases. 
 
 It also throws up new avenues for exploring the dynamics of plague: why a pandemic erupts and dies out, and how a novel strain emerges, becoming a threat against which the immune system has no defence. 
 
 ?We know the bacterium Y. pestis has jumped from rodents into humans throughout history, and rodent reservoirs of plague still exist today in many parts of the world," said Dave Wagner, an associate professor in the Center for Microbial Genetics and Genomics at Northern Arizona University. 
 
 "If the Justinian plague could erupt in the human population, cause a massive pandemic, and then die out, it suggests it could happen again." 
 
 Wagner added: "Fortunately we now have antibiotics that could be used to effectively treat plague, which lessens the chances of another large scale human pandemic." 
 
 'Intrinsically high virulence' 
 
 The samples used in the research came from two individuals buried in a mediaeval graveyard in Aschheim, Bavaria, and whose remains were dated to around 504 and 533 AD respectively. 
 
 Assembling their genomes is a feat, for they are the DNA codes of the oldest pathogens obtained to date. 
 
 Comparing the mediaeval strain to 131 Y. pestis bacteria in a database of the Black Death and 19th century plagues, the investigators concluded the Plague of Justinian came to the West out of Asia, as did the two later pandemics. 
 
 The 6th-century germ came equipped with a tool kit "of intrinsically high virulence," they write. 
 
 Helped by trade, poor hygiene and lack of immune defence among the host populations, this made the bacterium extraordinarily lethal, killing up to 40 percent of those it infected. 
 
 Less clear, though, is whether the pandemic germ was a cataclysm that almost literally came out of nowhere, or the culmination of a buildup -- possibly over centuries -- from isolated outbreaks. 
 
 As to why the plague disappeared and re-emerged seven centuries later, two theories are held. 
 
 One is that after infecting so many people, levels of immunity built up in the population, making it difficult for the germ to spread successfully. 
 
 Another is natural variation in climate which disrupted the conditions in which the germ spread. 
 
 Before each of the three plague pandemics, there was a spell of exceptional rainfall, and the climate was also unstable when these outbreaks ended, the study says. 
 
 Plague remains a background problem in some countries. Between 1,000 and 2,000 cases of plague are reported to world health watchdogs each year, although this figure is probably conservative, according to the US Centers for Disease Control and Prevention (CDC). 
 
 Copyright © 2014 AFP. All rights reserved. More » ||||| Many centuries before the Black Death wiped out a third to half of Europe, an equally virulent pandemic called the Plague of Justinian killed upwards of 100 million people in just two short years between 541 and 543 A.D. 
 
 Scientists have long debated the connection between what have been called the two most deadly plagues to wreak havoc on humankind. Now, an international team of researchers analyzing the remains of two people killed by the Plague of Justinian has concluded that the pandemics arose from two distinct strains of the bacterium Yersinia pestis. 
 
 The strain that caused the Plague of Justinian likely went extinct long before the emergence of the Black Death in the 14th century. 
 
 This is actually disturbing news for people today, the researchers said. Their findings imply that if such horrible strains of plague bacteria arose twice before, independently, there's no reason why another strain can't arise tomorrow … lurking today in the gut of a flea nesting in the fur of a rat. 
 
 This latest research appears today (Jan. 27) in the journal Lancet Infectious Disease. 
 
 The bacterium that causes the bubonic plague, Yersinia pestis, resides in the intestines of certain fleas that feed on rodents. A bite from an infected flea can spread the disease to humans. [6 Superbugs to Watch Out For] 
 
 "Plague remains a real threat in some places of the world, like Madagascar, which has more human plague cases than any other country — hundreds to over a thousand cases a year," said Dr. Dave Wagner, co-first-author on the study and an associate professor in the Center for Microbial Genetics and Genomics at Northern Arizona University. 
 
 Even the United States sees an average of seven bubonic plague infections yearly, from a strain introduced to California from China about 100 years ago. 
 
 Bubonic plague is curable with antibiotics if treated within a few days after infection. This and the fact that most people in wealthier countries don't live in close proximately to flea-carrying rodents — unlike the situation in medieval Europe and Asia — means that the chances of a plague pandemic are unlikely. 
 
 Nevertheless, a bubonic plague epidemic could rip through poor countries lacking proper hygiene, killing viciously and indiscriminately in just a few days upon infection. 
 
 "The main reason why there are a lot of plague cases in Madagascar is because they have large populations of non-native rats, which are good hosts for plague," Wagner told LiveScience. In the United States, the hosts often are other kinds of rodents, such as prairie dogs. 
 
 Previously, Wagner worked on the research team that established that the Plague of Justinian was indeed a bubonic plague caused by Yersinia pestis, settling a long-standing debate. They made this conclusion through DNA analysis of two victims of that plague. 
 
 The new study probed deeper and compared this unearthed Justinian bacterial strain to the well-studied Black Death strain. The researchers isolated miniscule DNA fragments from the teeth of those same two victims, both buried in Bavaria, Germany. (This feat itself resulted in obtaining the oldest known human pathogen genome.) 
 
 Using these DNA fragments, the researchers reconstructed the Yersinia pestis genome and compared it to a database of genomes from more than one hundred contemporary strains. The scientists found that this more ancient strain was an evolutionary "dead end," distinct from strains involved in the Black Death and subsequent outbreaks. 
 
 In fact, the third and most recent bubonic plague pandemic, which originated in Hong Kong around 1850 and killed millions, stems from the very same Black Death plague that decimated Europe, the researchers found. In other words, the ancient strain was gone, and only the Black Death strain remained to cause the 1850 pandemic. 
 
 "[This] research is both fascinating and perplexing, [and] it generates new questions, which need to be explored," said Dr. Hendrik Poinar, the senior author on the study and the director of the McMaster Ancient DNA Centre at McMaster University in Hamilton, Ontario. "For example, why did this [Justinian] pandemic, which killed somewhere between 50 and 100 million people, die out?" 
 
 Poinar said he hopes the study of ancient genomes can answer such questions, thereby helping prevent such pandemics today. 
 
 The researchers also determined that the Justinian strain likely originated in Asia, though some have speculated it started in Africa. But the scientists don't know when. Earlier epidemics, such as the Plague of Athens (circa 430 B.C.) and the Antonine Plague (circa 165 A.D.), could also be independent emergences of particularly virulent Yersinia pestis strains. 
 
 Doctors warn that pandemics can take many forms and remain a constant threat in this world of rapid global transportation and migration. The last great pandemic was the 1918 flu pandemic, which infected 500 million people and killed at least 75 million. The HIV/AIDS pandemic has taken approximately 30 million human lives since 1980. 
 
 The bubonic plagues, however, were extreme in killing such a high percentage of the European population — indeed, arguably, the cause of societal changes that ended the classical era of antiquity and then, 800 years later, gave birth to the Renaissance. 
 
 Follow Christopher Wanjek @wanjek for daily tweets on health and science with a humorous edge. Wanjek is the author of "Food at Work" and "Bad Medicine." His column, Bad Medicine, appears regularly on Live Science.
– The Plague of Justinian and the Black Death arose from separate bacteria strains, researchers say—and that's not a good thing, because if distinct plagues have ravaged the human population before, they could come up again, LiveScience reports. A group of researchers came to this conclusion by digging up two victims of the Black Death in Germany and studying DNA fragments in their teeth. They reconstructed the disease's genome and compared it to more than a hundred contemporary strains of plague, but no luck—the Black Death was an evolutionary dead end. This "generates new questions," says the study's top author. "For example, why did this [Justinian] pandemic, which killed somewhere between 50 and 100 million people, die out?" Maybe people built up an immunity to the bacteria, AFP notes, or natural climate variation could have stopped the germs from spreading. Either way, plague remains a threat in some countries, like Madagascar, where people live in closer proximity to flea-carrying rodents. Even the US has a few bubonic plague infections each year. "Fortunately we now have antibiotics that could be used to effectively treat plague, which lessens the chances of another large scale human pandemic," says a co-author of the study.