Investigations on the prevalence of Heterophyes species in twelve populations of the first intermediate host in Egypt and Sudan.

Twelve populations of the mud snail Pirenella conica from the densely populated Nile Delta, saline inland waters, and the scarcely populated coast of the Red Sea were investigated for the prevalence of Heterophyes heterophyes, H. aequalis, and H. dispar. Heterophyes heterophyes was most prevalent in the Nile Delta, which seems to be the centre of human heterophyiasis throughout the distributional range of that species. Transmission takes place near human settlements, where the definitive hosts are abundant. However, the compiled data from infected intermediate and definitive hosts show, that the prevalence of H. heterophyes in the Nile Delta is declining. The two other Heterophyes species of the Near East, which have not yet been recorded from humans, were absent (H. dispar) or almost absent (H. aequalis) from the Nile Delta, where they had been found frequently in the 1950s. However, they occurred at the coast of the Red Sea.