I am investigating alien rodents that occur within Japanese Islands for their parasitic nematodes, because some alien nematodes derived from such alien hosts could become highly pathogenic agents to human and livestock, and because the parasites potentially could switch their hosts to and having a negative impact on native host-parasite relationships that have evolved as a result of adaptive radiation or co-speciation between the native rodents and parasitic nematodes. I am generalizing the patterns of host-parasite associations, and providing 4 types: alien rodents and alien nematodes such as Callosciurus erythraeus and Brevistriata callosciuri, and Myocastor coypus and Strongyloides myopotami; alien rodents and native nematodes such as Rattus rattus and Heligmosomoides kurilensis shifted from Apodemus speciosus; native rodents and alien nematodes such as Apodemus argenteus and Heligmosomoides polygyrus shifted from Mus musculus; native rodents and native nematodes such as Apodemus spp. and Heligmosomoides spp. Hence, aberrant host-parasite relationships due to the presence of alien rodents and/or nematodes comprise the 1st, 2nd and 3rd groups. These relationships should be discriminated from the native host-parasite relationships within Japanese natural ecosystem. Some potential strategies including monitoring survey for reduction of risk affected by the aberrant relationships were discussed.