"History books have long taught the Black Death, which wiped out a quarter of Europe's population in the Middle Ages,
was caused by bubonic plague, spread by infected fleas that lived on black rats. But new research in England suggests the
killer was actually an Ebola-like virus transmitted directly from person to person." from
http://abcnews.go.com/sections/living/DailyNews/blackdeath_010730.html
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