The detection of encapsulated and non-encapsulated species of Trichinella suggests the existence of two evolutive lines in the genus

In recent years, the discovery of many non-encapsulated isolates of Trichin ella, designated Trichinella pseudospiralis and the identification of a new non-encapsulated species, Trichinella papuae, has revealed that the biomas s of the genus Trichinella does not only include the well known encapsulate d species (T. spiralis, T. nativa, T. britovi, T. murrelli, and T. nelsoni) but also includes geographically disseminated, non-encapsulated species th at represent important biological entities in the genus. larvae of the firs t stage (L-1) 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 encapsu lated species diverge with respect to their developmental strategies where L-1 of encapsulated species are able to induce the nurse cell to synthesize collagen, unlike non-encapsulated larvae which do not induce collagen prod uction. The presence or absence of a collagen capsule is of greet importanc e in the natural cycle of these parasites in that it allows the encapsulate d larva to survive, to substantially longer periods of time and therefore r emain infective even within putrefied muscle tissue.