Submitted to: Veterinary Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/15/2003
Publication Date: 10/10/2004
Citation: Zarlenga, D.S., Larosa, G., Pozio, E., Rosenthal, B.M. 2004. Identification and classification within the genus trichinella, with special emphasis on non-encapsulated species. Veterinary Parasitology. 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 implicating the avian species, T. pseudospiralis, as a pathogen in humans has prompted research on population differences and host specificities within this species. Scientific evidence is mounting suggesting that the non-encapsulated species constitute a phylogenetically diverse group that is distinct from the capsule-forming species of Trichinella Herein, we propose a reclassification of the genus based upon new molecular and biochemical data. This finding will assist researchers in determining whether certain populations of this species are more infectious to humans than others.
Technical Abstract: Since James Paget and Richard Owen first described Trichinella in 1835, three basic points of view have emerged on the organization of the genus; 1) those that consider the genus monospecific and made up of numerous isolates or subspecies;2) those that subdivide it into 4 species consisting of T. spiralis, T. nativa, T. nelsoni and T, pseudospiralis, with a collection of geographical isolates, and; 3) the most current belief that the genus is partitioned into 8 species with at least 1 additional genotype (Trichinella T6) whose classification remains undetermined. Where views 1 and 2 have their foundations primarily in historical opinion and infectivity data, classification scheme 3 is supported by these considerations as well as molecular and biochemical data, cross-breeding experiments, and methodically analyzed biological information. Nonetheless, the classification of this genus remains in flux. With the identification of three non-encapsulated species, T. pseudospiralis, T. papuae and T. zimbabwensis, and the delineation of biological and biochemical characters among isolates of T. pseudospiralis, evidence is mounting for segregating the non-encapsulated group from those that induce capsule formation. This presentation will outline methods for differentiating Trichinella parasites, review current support for the multiple species concept, and provide a molecular foundation for considering non-encapsulated species as a unique group, based primarily upon sequence information from genomic ITS and mitochondrial DNA, expansion segment V of the lsu rDNA, and newly described glutamic acid rich genes specifically expressed in newborn larvae.