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. summary 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. transmission main article: black death migration lack of hygiene 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. by the early fourteenth century so much filth had collected inside urban europe that french and italian cities were naming streets after human waste. in medieval paris, several street names were inspired by merde, the french word for "shit". there were rue merdeux, rue merdelet, rue merdusson, rue des merdons and rue merdiere—as well as a rue du pipi. pigs, cattle, chickens, geese, goats and horses roamed the streets of medieval london and paris. medieval homeowners were supposed to police their housefronts, including removing animal dung, but most urbanites were as careless as william e. cosner, a resident of the london suburb of farringdon without. a complaint lodged against cosner charges that "men could not pass for the stink . . . horse dung and horse piss." one irate londoner complained that the runoff from the local slaughterhouse had made his garden "stinking and putrid", while another charged that the blood from slain animals flooded nearby streets and lanes, "making a foul corruption and abominable sight to all dwelling near." in much of medieval europe, sanitation legislation consisted of an ordinance requiring homeowners to shout, "look out below!" three times before dumping a full chamber pot into the street. early christians, who thought self-abnegation a cardinal virtue, considered bathing, if not a vice, then a temptation. "who knows what impure thoughts might arise in a tub of warm water? with this danger in mind, st. benedict declared, "to those who are well, and especially to the young, bathing shall seldom be permitted." st. agnes took the injunction to heart and died without ever bathing. territorial origins 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" over 2,600 years ago. 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. however more recent research notes that the previous sampling had a very heavy east asian bias and that sampling since then has discovered strains of y. pestis in the caucasus region that were previously thought to be restricted to china. there is also no physical or specific textual evidence of the black death in 14th century china. as a result, china's place in the sequence of the plague's spread is still debated to this day. according to charles creighton, records of epidemics in 14th century china suggest nothing more than typhus and major chinese outbreaks of epidemic disease post-date the european epidemic by several years. the earliest chinese descriptions of the bubonic plague do not appear until the 1640s. 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; this is supported by recent direct findings of y. pestis dna in teeth samples from graves in the area with inscriptions referring to "pestilence" as the cause of death. epidemics killed an estimated 25 million across asia during the fifteen years before the black death reached constantinople in 1347. the evidence does not suggest, at least at present, that these mortality crises were caused by plague. although some scholars, including mcneill and cao, see the 1333 outbreak as a prelude to the outbreaks in europe from the late 1340s to the early 1350s, scholars of the yuan and ming periods remain skeptical about such an interpretation. nonetheless, the remarkably high mortality rates during the datong mortality should discourage us from rejecting the possibility of localized/regional outbreaks of plague in different parts of china, albeit differing in scale from, and unrelated to, the pandemic mortality of the black death. what we lack is any indication of a plague pandemic that engulfed vast territories of the yuan empire and later moved into western eurasia through central asia.— philip slavin according to john norris, evidence from issyk-kul indicates a small sporadic outbreak characteristic of transmission from rodents to humans with no wide-scale impact. according to achtman, the dating of the plague suggests that it was not carried along the silk road, and its widespread appearance in that region probably postdates the european outbreak. there are no records of the symptoms of the black death from mongol sources or writings from travelers east of the black sea prior to the crimean outbreak in 1346. finally, the silk road had already been heavily disrupted before the spread of the black death. western and middle eastern traders found it difficult to trade on the silk road by 1325 and impossible by 1340, making spread of the plague less likely. others still favor an origin in china or even kurdistan, and not central asia. according to the theory of chinese origin, the disease may have traveled along the silk road with mongol armies and traders, or it could have arrived via ship, but this theory is still contested. it is speculated that rats aboard zheng he's ships in the 15th century may have carried the plague to southeast asia, india and africa. 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. demographic historians estimate that china's population fell by at least 15 percent, and perhaps as much as a third, between 1340 and 1370. this population loss coincided with the black death that ravaged europe and much of the islamic world in 1347–52. however, there is a conspicuous lack of evidence for pandemic disease on the scale of the black death in china at this time. war and famine – and the diseases that typically accompanied them – probably were the main causes of mortality in the final decades of mongol rule.— richard von glahn monica h. green suggests that the reason why other parts of eurasia outside the west do not contain the same evidence of the black plague is because there were actually four strains of yersinia pestis that became predominant in different parts of the world. mongol records of illness such as food poisoning may have been referring to the black plague. another theory is that the black death originated near europe and cycled through the mediterranean, northern europe and russia before making its way to china. other historians such as john norris and ole benedictaw believe the black death likely originated in europe or the middle east and never reached china. european outbreak the seventh year after it began, it came to england and first began in the towns and ports joining on the seacoasts, in dorsetshire, where, as in other counties, it made the country quite void of inhabitants so that there were almost none left alive.... 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. geoffrey the baker, chronicon angliae 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