Submitted to: International Journal for Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/20/2001
Publication Date: 9/21/2001
Citation: Interpretive Summary: Speciation within the genus Trichinella remains a controversial issue, notwithstanding the problems associated with population differences and host specificity among the genotypes. Recent reports of outbreaks suggesting the avian species, T. pseudospiralis, as a pathogen in humans has prompted research on population differences and host specificities within the species that do not encapsulate within the muscles of infected animals. Herein, we examine 11 geographical isolates of T. pseudospiralis and 1 isolate of T. papuae with respect to host infectivity and numerous biochemical and molecular markers. Results demonstrated;1) that T.papuae is clearly a distinct species from T. pseudospiralis; 2) that several molecular characters can be used to delineate these species; and 3) that geographical segregation exists between T. pseudospiralis populations from different zoogeographical regions. The identification and genetic characterization of zoogeographical strains of T. Pseudospiralis is of great significance not only for its taxonomic and phylogenetic value, but also because of the well-documented potential for human infection by this species and the importance of being able to delineate the geographical source of the acquired trichinellosis through molecular markers similar to those identified herein. These findings will therefore assist researchers in determining whether certain populations of this species are more infectious to humans than others.
Technical Abstract: The low number of non-encapsulated isolates of Trichinella studied thus far has deterred our ability to understand their level of differentiation from encapsulated species and has hindered evaluations of the taxonomic value of the observed polymorphisms. To this end, biological, biochemical and molecular data from 11 isolates of Trichinella pseudospiralis and 1 isolate eof 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. Also, in contrast to T. pseudospiralis, T. papuae failed to infect chickens. Comparative analysis of 12 allozymes revealed a single difference among Nearctic and Australian isolates of T. pseudospiralis but substantial lvariation when compared with T. papuae, i.e., 2 unique and 6 diagnostic markers. Molecular studies involving mitochondrial-derived genes encoding cytochrome oxidase I and the large subunit ribosomal DNA (lsrDNA) indicated a high level of sequence similarity among T. pseudospiralis isolates; however, a concomitantly high level of variation was observed in expansion segment V of the genomic lsrDNAs among T. pseudospiralis isolates and between this species and T. papuae. Collectively, these results support high uniformity among isolates of T. pseudospiralis from Eurasia and polymorphism among isolates of T. pseudospiralis belonging to different zoogeographical regions, and corroborates the classification of T. papuae as a differentiated species.