![]() For example, the models in the current study did not account for local conditions that could have affected disease transmission, such as war, famine, immunity and public health interventions, they said. The researchers noted that their models could be improved with more data. ![]() "Overall, our results suggest that plague transmission in European epidemics occurred predominantly through human, rather than commensal rat or pneumonic transmission," the researchers wrote in their paper. Using publicly available data on plague deaths in nine regions during the second pandemic, the researchers found that the human parasite model best reflected death rates in seven of the nine regions, compared with the other two models. One model assumed the disease was spread from rats to fleas to people a second model assumed the disease was spread from human fleas and body lice to other people and a third model assumed the disease was spread from person to person through the air, which occurs only when people develop a form of plague known as pneumonic plague. In the new study, the researchers used mathematical equations to create three different models of plague transmission during a series of outbreaks in Europe called the second pandemic, which includes the Black Death and occurred during the 14th through 19th centuries. For example, fleas and lice could have fed on infected humans, and then transmitted the disease to other humans. ![]() This has led some researchers to speculate that human parasites played an important role in spreading the Black Death. And the Black Death spread much farther and faster, and killed many more people, than modern outbreaks do, the study authors said. For instance, records from the time do not mention large numbers of rats dying off, as was seen in later outbreaks in Europe starting in the 19th century, according to the new study. ![]() But some researchers argue that this mode of transmission doesn't fit with the historical evidence. ![]()
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