The spread of freshwater snails including those of medical and veterinary importance.

The present paper discusses the spread of freshwater snails that act as intermediate hosts for various trematodes that cause diseases in man and in cattle. Examples of snail species which have spread across natural barriers are reviewed as well as the mechanisms involved in this transport. Focus is put on the extensive trade in freshwater aquatic plants and aquarium fish, and the need for better control of this trade is emphasized in order to minimize the risk of unintended import of potentially harmful snails.