Introduction

Summary

The Seventh Pandemic was different from the first six in several respects. Its agent was a new biotype of the cholera pathogen, Vibrio cholerae 01 El Tor. Evolutionary biology suggests why El Tor was able to replace the more virulent classic cholera. Natural selection favored the more benign El Tor; although classic cholera killed its victims more quickly, it lost opportunities to infect more potential hosts. Patients with milder El Tor, less severely ill, were more mobile and could infect others at greater distance and over a longer period of time. Classic cholera in the earlier pandemics traveled from country to country and moved only as quickly as available transport permitted, but the Seventh Pandemic leap-frogged continents by air and benefited from faster ships, trains, and automobiles. It also lasted longer than any of the earlier pandemics. After forty-eight years it shows no sign of abating today.

The diminished impact of the sixth cholera pandemic led many experts to believe that the world was seeing the last of this terrible calamity. Europe's last case dated back to the 1920s, and Mecca's to 1912. Regular reports of cholera did surface from time to time in its traditional home in South Asia, but pandemics seemed to have disappeared.

Researchers first labeled the new biotype (Vibrio cholerae 01 El Tor) “paracholera” because it was initially confined not to cholera's original home in the Ganges Delta, but, from its first appearance in 1937 through to 1960, to Indonesia.