A number of important aspects of infection with C. sinensis, O.
felineus and O. viverrini are evident. Particularly interesting is the
zoonotic gradient between an almost completely zoonotic cycle
of O. felineus in Europe through a combined zoonotic and human
cycle in Siberia, a combined cycle in C. sinensis and a largely
anthropogenic cycle in O. viverrini. Nevertheless, all species show
strong epidemiological similarities. They have a strongly restricted
number of first intermediate snail hosts, a wide range of predominantly
cyprinid fish hosts, and a scattering of mammalian, mainly
carnivorous, final hosts. This presents a situation in which the
influence of humans on the evolution of the parasites, despite
the similarities in the life cycle of all species, differs considerably
between species. It therefore offers us with the opportunity to address
questions involving the role of humans in parasite evolution.