<P> An estimate of the mortality rate for the modern bubonic plague, following the introduction of antibiotics, is 11%, although it may be higher in underdeveloped regions . 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 per cent die within eight days . Pneumonic plague has a mortality rate of 90 to 95 per cent . Symptoms include fever, cough, and blood - tinged sputum . As the disease progresses, sputum becomes free - flowing and bright red . Septicemic 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 septicemic 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 . </P> <P> A number of alternative theories--implicating other diseases in the Black Death pandemic--have also been proposed by some modern scientists (see below--"Alternative Explanations"). </P> <P> In October 2010, the open - access scientific journal PLoS Pathogens published a paper by a multinational team who undertook a new investigation into the role of Yersinia pestis in the Black Death following the disputed identification by Drancourt and Raoult in 1998 . 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". </P> <P> The study also found that there were two previously unknown but related clades (genetic branches) of the Y. pestis genome associated with medieval mass graves . These clades (which are thought to be extinct) were found to be ancestral to modern isolates of the modern Y. pestis strains Y. p. orientalis and Y. p. medievalis, suggesting the plague may have entered Europe in two waves . Surveys of plague pit remains in France and England indicate the first variant entered Europe through the port of Marseille 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 epidemics . Surveys of plague pit remains from the Dutch town of Bergen op Zoom showed 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 Bergen op Zoom (and possibly other parts of the southern Netherlands) was not directly infected from England or France in 1349 and suggesting a second wave of plague, different from those in Britain and France, may have been carried to the Low Countries from Norway, the Hanseatic cities or another site . </P>

Who discovered the cause of the black death