The environmental reservoirs and vector of Vibrio cholerae

Cholera is a life-threatening diarrheal disease that can spread rapidly and in explosive epidemics from one region to another, affecting large numbers of people. V. cholerae, a gram-negative motile bacterium, is the causative agent of this intestinal disease. To date, more than 200 serogroups of V. cholerae have been recorded, of which only two (O1 and O139) have been associated with major epidemics. Cholera spreads in pandemics; however, the mechanism that enables V. cholerae to cross water bodies, including oceans, is still puzzling. V. cholerae proliferates while attached to or associated with eukaryotic organisms in the aquatic environment, particularly copepods (Crustacea). Chironomids (Diptera) were also found to serve as intermediate 'host' reservoirs for V. cholerae. Recently, it was found that both copepods and chironomids are dispersed by migratory waterbirds, which either consume them (endozoochory) or carry them externally (epizoochory). Evidence on epidemic V. cholerae strains that were isolated from waterbirds was published about twenty years ago but failed to attract the attention of the scientific community. Hence we conclude that waterfowl might be responsible for the dissemination of V. cholerae between continents, and thus for the pandemicity of cholera. Better understanding of the species of waterfowl that carry V. cholerae and their migration patterns might therefore be useful in predicting future outbreaks of cholera.