Vibrios are highly motile, gram-negative, curved or comma-shaped rods with a single polar flagellum. Of the vibrios that are clinically significant to humans, Vibrio cholerae O group 1, the agent of cholera, is the most important. Vibrio cholerae was first isolated in pure culture by Robert Koch in 1883, although it had been seen by other investigators, including Pacini, who is credited with describing it first in Florence, Italy, in 1854.

Cholera is a life-threatening secretory diarrhea induced by an enterotoxin secreted by V cholerae. Cholera and the cholera enterotoxin are increasingly recognized as the prototypes for a wide variety of non-invasive diarrheal diseases, collectively known as the enterotoxic enteropathies; of these, diarrhea due to enterotoxigenic strains of Escherichia coli (see Ch. 26) is the most important. Cholera remains a major epidemic disease. There have been seven great pandemics. The latest, which started in 1961, invaded the Western Hemisphere (for the first time this century) with a massive outbreak in Peru in 1991. There have since been more than a million cases in Central and South America as well as a few imported cases in the U.S. and Canada. V cholerae serogroup O139, which arose in October of 1992 in India and Bangladesh, may become the cause of the 8th great pandemic of cholera.

Other vibrios may also be clinically significant in humans, and some are known to cause diseases in domestic animals. Nonpathogenic vibrios are widely distributed in the environment, particularly in estuarine waters and seafoods. For this reason, isolation of a vibrio from a patient with diarrheal disease does not necessarily indicate an etiologic relationship.