Assessment of parenteral Plagiorhynchus cylindraceus (Acanthocephala) infections in shrews

Plagiorhynchus cylindraceus, a common acanthocephalan parasite of passerine birds, does not require a paratenic host for completion of the life cycle, but extraintestinal (parenteral) infection do occur in short-tailed shrews (Blarina brevicauda). Examination of wild mammals trapped at 13 sites in a nd around Lincoln, Nebraska, U.S.A., revealed infections in short-tailed sh rews and a masked shrew (Sorex cinereus) but not in any other species of ma mmals collected. Laboratory exposures of B. brevicauda and 5 other mammalia n species that co-occur with short-tailed shrews at sites where shrews harb or extraintestinal P. cylindraceus infections resulted in infections only i n short-tailed shrews and a single deer mouse (Peromyscus maniculatus). A c ystacanth obtained from the mesentery of 1 of these shrews was infective wh en fed to a robin (Turdus migratorius), the usual definitive host. Intestin al histology and susceptibility of P. maniculatus to laboratory infections suggest that the absence of parenteral infections in mammals other than shr ews is due to ecological circumstances rather than physiological or anatomi cal constraints. Laboratory exposures of 3 species of isopods and a survey of isopods collected form a site where infected shrews occur failed to reve al any species susceptible to P. cylindraceus other than the only known int ermediate host, the terrestrial isopods Armadillidium vulgare. An analysis of the literature regarding diets and the fact that deer mice did not prey on A. vulgare in laboratory feeding trials suggest that other mammals co-oc curring with shrews are unlikely to consume the intermediate host of P. cyl indraceus.