Trichinella pseudospiralis populations of the Palearctic region and their relationship with populations of the Nearctic and Australian regions

Since few non-encapsulated isolates of Trichinella have been studied to date, their level of differentiation from encapsulated species and the taxonomic value of the observed polymorphisms remain to be determined. To this end, biological, biochemical and molecular data from 11 isolates of Trichinella pseudospiralis and one isolate of Trichinella papuae were examined using the broad group of encapsulated species and genotypes for comparison. Single-worm cross-breeding experiments and reproductivity capacity indices revealed F1 progeny only among T. pseudospiralis isolates from different zoogeographical regions, whereas no F1 were produced when T. pseudospiralis was crossed with T. papuae. Furthermore, unlike T. pseudospiralis, T. papuae failed to infect chickens. Comparative analysis of 12 allozymes revealed a single difference between Nearctic and Australian isolates of T. pseudospiralis, but substantial differences when compared with T. papuae (i.e. two unique and six diagnostic markers). Molecular studies involving mitochondrial-derived genes encoding cytochrome oxidase I and the large subunit ribosomal DNA indicated a high level of sequence similarity among T. pseudospiralis isolates; however, a concomitantly high level of variation was observed in expansion segment five of the genomic large subunit ribosomal DNAs among T. pseudospiralis isolates and between this species and T. papuae. Collectively, these results demonstrate high uniformity among isolates of T. pseudospiralis from Eurasia and polymorphism among isolates of T. pseudospiralis belonging to different zoogeographical regions; the results corroborate the classification of T. papuae as a differentiated species.