Submitted to: Parasite
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 28, 2001
Publication Date: January 30, 2002
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 that; 1) T.papuae is clearly a distinct species from T. pseudospiralis; 2) several molecular characters can be used to delineate these species; and 3) geographical segregation exists between T. pseudospiralis populations from different zoogeographical regions. The identification and genetic characterization of fzoogeographical strains of T. pseudospiralis is of great significance not only for their 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. These findings will therefore assist researchers in determining whether certain populations of this species are more infectious to humans than others.
In recent years, the discovery of many non-encapsulated isolates of Trichinella, designated Trichinella pseudospiralis and the identification of a new non-encapsulated species, Trichinella papuae, has revealed that the biomass of the genus Trichinella does not only include the well known encapsulated species (T. spiralis, T. nativa, T. britovi, T. murrelli, and T. nelsoni) but also includes geographically disseminated, non-encapsulated species that represent important biological entities in the genus. Larvae of the first stage (L1) of both non-encapsulated and encapsulated species are able to penetrate the muscle cell and induce a dedifferentiation of this cell. But following this point in the parenteral cycle, non-encapsulated and encapsulated species diverge with respect to their developmental strategies where L1 of encapsulated species are able to induce the nurse cell to synthesize collagen, unlike non-encapsulated larvae which do not induce collagen production. The presence or absence of a collagen capsule is of great importance in the natural cycle of these parasites in that it allows the encapsulated larva to survive to substantially longer periods of time and therefore remain infective even within putrefied muscle tissue. This as well as isoenzyme and genetic data suggest that the genus Trichinella be split into 2 distinct genera.