WASHINGTON (Reuters) - The plague germ that caused the "Black Death" in the 14th century and other ferocious pandemics has stalked humankind far longer than previously known.br clear='all'/img width='1' height='1' src='http://reuters.us.feedsportal.com/c/35217/f/654220/s/4ae5da3c/sc/3/mf.gif' border='0'/div class="feedflare"
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