text: Black death 'discriminated' between victims
  The Black Death that decimated populations in Europe and elsewhere during the middle of the 14th century may not have been a blindly indiscriminate killer as previously believed.
  An analysis of 490 skeletons from a London cemetery for Black Death victims shows the infection did not affect everyone equally, researchers say.
  Anthropologists Dr Sharon DeWitte, of the University at Albany in New York and Pennsylvania State University's Professor James Wood say many perfectly healthy people were killed by the plague.
  However, writing in the latest Proceedings of the National Academy of Sciences, they say those already in poor health before the pandemic were more likely to have perished.
  "A lot of people have assumed the Black Death killed indiscriminately, just because it had such massive mortality," DeWitte says.
  "There's been a tradition of thinking that the Black Death was this unique case where no one was safe and if you were exposed to the disease that was it.
  "You had three to five days, and then you were dead."
  The researchers found however that the state of people's health before contracting the disease played a role in whether they survived.
  The plague of 1347 to 1351 was one of the deadliest epidemics in human history, killing about 75 million people, according to some estimates, including up to 50% of the European populations affected.
  It was called the Black Death because of the black spots the bubonic form of the plague caused on the skin.
  DeWitte and Wood analysed skeletons unearthed during excavations in the 1980s from London's East Smithfield Black Death cemetery.
  For comparison they used 291 pre-Black Death skeletons from Denmark during the same era.
  The scientists estimated the victim's age at their time of death and looked for bone abnormalities that would show people had health problems before they died of plague.
  They found such abnormalities in many of the skeletons, suggesting these people had experienced malnutrition, iron deficiencies and infections well before the arrival of the Black Death.
  The proportion of London skeletons showing signs of poor health compared with those in relative good health, indicated the plague was selective in who it killed, the researchers report.
  The most likely reason for frail victims' deaths was that poor nutrition weakened their immune response, the authors say.
  They say experts have believed the Black Death killed indiscriminately because it was so virulent and the European population so immunologically unprepared.
  "The Black Death was highly virulent and undoubtedly killed many otherwise healthy people who would have been unlikely to die under normal-mortality conditions," they write.
  "The results suggest the Black Death did not kill indiscriminately, but it did discriminate less sharply than death normally does."
  Scientists think the plague was caused by Yersinia pestis, a bacterial disease spread by fleas from rats. It still kills between 100 and 200 people a year.