WATERBIRDS AS POSSIBLE VECTORS OF VIBRIO CHOLERAE

V. cholerae, the causative agent of cholera is a natural inhabitant of aquatic ecosystems where it can exist in a free-living planktonic form or associate with copepods and chironomids. Cholera can spread rapidly in epidemics and pandemics, however, the mechanism that enables the bacteria to cross water bodies is still puzzling. It was found that both copepods and chironomids are dispersed by migratory waterbirds. We hypothesized that migratory birds which consume or carry externally chironomids and copepods, may distribute V. cholerae among water bodies. In addition, in the food chain, fish may link chironomids and copepods to waterbirds. We were able to isolate V. cholerae from the intestine of several fish and waterbirds species, demonstrating that indeed waterbirds may be vectors of the cholera bacterium. For finding further evidence to our hypothesis, we studied cormorants (Phalacrocorax carbo)that lived in captivity. These cormorants did not contain V. cholerae in their droppings. The cormorants were divided into two groups that were fed with two different fish species; (1) Tilapia fish (Oreochromis aureus x niloticus) that contained V. cholerae in their intestine and (2) Golden fish(Carassius auratus auratus) that did not contain the bacteria. V. cholerae was isolated only from bird droppings that were fed with Tilapia fish. These demonstrated that waterbirds get infected with V. cholerae when feeding on fish that are contaminated with the bacteria. We conclude that waterbirds can act as vectors of the bacteria and that the transfer of the bacteria to the waterbirds may occur via fish consumption. Waterbirds movement across intercontinental borders provides a possible mechanism for the global distribution of V. cholerae.