Liver fluke egg. Macro photograph of a liver fluke (Fasciola hepatica) egg, showing the embryo inside. Adult liver flukes are parasitic tremotode flatworms that live in the bile duct of various mammals. They cause a disease known as fasciolosis and can cause great economic losses in the sheep and cattle industry. This egg will develop into a miracidium larva which infects the intermediate host, Lymnaea truncatula snails, before developing further into the adult fluke.