The association between snails carrying parasites or their larvae and the infections they cause in humans, who are usually exposed to the snails in natural bodies of water. Clonorchiasis is a chronic parasitic infestation of the liver in humans that is caused by the ingestion of freshwater fish containing the larvae of the liver fluke, which have undergone a stage of their development in the liver glands of water snails. Swimmer’s itch is caused by parasites of birds and mammals that are carried by infected snails and released into natural bodies of fresh water by the snails.