Myofibre changes and capsule formation in mice infected with different strains of Trichinella.

Mice were infected with 4 strains of Trichinella with the purpose of describing muscle changes (M. Gastrocnemius, diaphragma) by light and electron microscopy, paying particular attention to capsule formation in a polar bear isolate (T. no. 13). No differences in myofibre changes or capsule formation were observed between the different strains by light microscopy at 21 and 60 days post infection. Ultrastructural studies of meat samples 60 day post infection with T. no. 13 revealed active capsule formation in muscle fibres, characterized by protrusions and invaginations of the sarcolemma. Basal lamina-like material was located close to the sarcolemma and in a lattice-like pattern in the capsule matrix. T. no. 13 seems to have a migratory pattern similar to the other strains examined and induces muscle fibre changes undiscernible from those of the 3 other strains. Infected muscle cells are considered to be involved in capsule formation.