Transmission experiments on the host specificity of Heterophyes species in 16 potential definitive hosts.

Sixteen different species of piscivorous mammals and birds were tried as experimental definitive hosts for Heterophyes heterophyes, H. aequalis and H. dispar. The hosts were classified in four categories, by fluke longevity, recovery and size, and the number of uterine eggs (embryonated/unembryonated): (1) Canidae and the cat were highly susceptible hosts for all three species of Heterophyes; (2) several mammals and herons showed a reduced susceptibility to infection (H. aequalis, 6 species; H. dispar, 1 species; H. heterophyes, 0 species); (3) In a group of hosts specific to each trematode, flukes were recovered up to 14 days post infection, but their uterine eggs did not become embryonated; (4) In a fourth category of hosts, chiefly Mustelidae, flukes could not be recovered. Taking also the literature into account it is concluded that man is a highly susceptible host for H. heterophyes, and that probably H. aequalis and H. dispar may reach reproductive maturity in humans also. The described wide host range of H. aequalis appears to be more typical for Heterophyidae than the comparably narrow host range of H. heterophyes.