Great cormorants (Phalacrocorax carbo) as potential vectors for the dispersal of Vibrio cholerae

Vibrio cholerae is the cause of cholera, a devastating epidemic and pandemic disease. Despite its importance, the way of its global dissemination is unknown. V . cholerae is abundant in aquatic habitats and is known to be borne by copepods, chironomids and fishes. Our aim was to determine if fish-eating birds act as vectors in the spread of V . cholerae by consuming infected fish. We determined the existence of V . cholerae in the microbiome of 5/7 wild cormorants’ intestine. In three of these V . cholerae -positive wild cormorants, the presence of a gene for cholera toxin ( ctxA ) was detected. We subsequently tested eight captive, hand-reared cormorants, divided into two equal groups. Prior to the experiment, the feces of the cormorants were V . cholerae -negative. One group was fed exclusively on tilapias, which are naturally infected with V . cholerae , and the other was fed exclusively on goldfish or on koi that were V . cholerae -negative. We detected V . cholerae in the feces of the tilapia-fed, but not in the goldfish/koi-fed, cormorants. Hence, we demonstrate that fish-eating birds can be infected with V . cholerae from their fish prey. The large-scale movements of many fish-eating birds provide a potential mechanism for the global distribution of V . cholerae .