Mexico City commuters wore face-masks on Monday, to protect against
a deadly outbreak of swine flu that has killed 149 in Mexico. Cases of
infection have also been confirmed in the U.S. and at least four other
countries. The head of the World Health Organization has warned that
the deadly disease is a "serious situation" with "pandemic potential."
In today's TNR slideshow, we review the tragic consequences of past global pandemics.
Photo courtesy of Getty Images.