Existing reports on parasitic helminths were investigated for 24 species and 2 subspecies of alien mammals introduced into Japan. These reports described 10 trematode, 2 cestode, 1 acanthocephalan and 15 nematode species in 8 host species. Additionally, 1 alien nematode species each has been obtained from 2 species of alien mammals recently. The host species with the most helminth species reported in Japan is the racoon,
Procyon lotor, with 5 trematode and 6 nematode species, including
Baylisascaris procyonis, reported from this host species in some zoos in Japan. Most of these helminth species in introduced racoon were apparently transferred from native animals in Japan. The host species with the most reports on parasitic helminths is the Siberian weasel,
Mustela sibirica, with 4 trematode and 4 nematode species in 14 reports, although this host species was not differentiated from the Japanese weasel,
M. itatsi, in some reports, Most studies on the parasitic helminths of alien mammals have been conducted from the viewpoint of medicine and public health. However, it will become necessary to research and protect the native parasitic helminth faunas of wild Japanese mammals against the disturbance from alien parasitic helminths. It is suggested that the introduction of alien parasitic helminths of mammals into Japan may have become easy because the native helminths of Japanese mammals have often become extinct with the small host populations in the geographical conditions of Japan, and artificial reduction of the host populations. The disturbance of native helminth faunas is also considered an ubiquitous problem, even if some problems of alien organisms, such as competition with native organisms, do not apply in the case of alien parasitic helminths.
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