"When long-distance travel is rare, epidemics spread like a slow, rippling wave, as demonstrated by the simulation (left) and the actual historical spread of the black death during the Middle Ages.
Credit: Images courtesy of Oskar Hallatschek and D. Sherman and J. Salisbury"
Graphic source: http://www.sciencedaily.com/releases/2014/11/141105093508.htm
PUBLISHED ON THE WEB: February 23, 2000;
February 19, 2001
Updated: 12/29/2018 R316 (Entire page updated: 4/6/2016)
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Very comprehensive coverage 