Ultrastructural changes which occurred in infected skeletal muscle fibers after infection with larvae of Trichinella spiralis were followed on a daily basis utilizing synchronous infections. No changes were observed in muscle fiber architecture during the first 2 days of intracellular infection. However, on Day 3, a space containing various sarcoplasmic elements developed between the plasma membrane and myofilaments. Widening near the regions of triads was also observed at this time. On Day 4 the space at the outer edge had increased, as did the ones at the triads. In addition, the myofilaments throughout the infected fiber were in a state of partial disarray. Finally, the nuclei were enlarged and had migrated to the central portion of the infected cytoplasm. On Day 5 day, sarcomeres were highly disorganized, and an increase in sarcoplasmic reticulum (SR) was noted. By Day 8, only the extreme periphery of the infected fiber contained Z bands with actin filaments attached. Proliferation of the t tuble system was also evident. At Day 10, myofilaments were completely replaced with SR. Further, the plasma membrane became hyperinvoluted and was associated with a 36-fold increase in the thickness of the glycocalyx. No further enlargement of nuclei occurred after Day 10. Finally, a host-derived double membrane completely surrounded the larva.

Adaptive changes in muscle fibers infected with Trichinella spiralis.

Analysis of a 43-kDa glycoprotein from the intracellular parasitic nematode Trichinella spiralis.

Trichinella spiralis: growth of the intracellular (muscle) larva.

The encapsulation of Trichinella spiralis larvae in host striated muscle was studied.Capsule formation starts at 13 days post-infection. Between days 20–50 p.i. the largest increase in capsule formation was observed. The capsule is exclusively, or almost exclusively, formed from and by the infected muscle fibre, as might be concluded from the presence of the sarcolemmal basal lamina surrounding the capsule substance during the initial stages of capsule formation. A collagen nature of the capsule cannot be excluded.

Ultrastructural aspects of capsule formation in Trichinella spiralis infection in the rat.

1. 1. The nature of metabolic interaction during parasitic infection was discussed and the concept of metabolic integration outlined. The subjective nature of the integrative argument was noted. 2. 2. The parasite-host relationships of larval trematodes of the genus Schistosoma with their intermediate molluscan hosts, the nematode Trichnella spiralis and cestode Hymenolepis diminuta, with their definitive hosts, as well as the hymenopterous insect parasite, Hyposoter exiguae, with its insect host, Trichoplusia ni, were examined. 3. 3. The significance of the immune system in the establishment of the parasite-host association and the means by which parasites evade host defense were discussed. 4. 4. The involvement of microorganisms or “hyperparasites” during the host associations of multicellular parasites was described. 5. 5. The importance of evolutionary considerations in assessing the nature of metabolic interaction and its significance to the success of the parasite-host relationship was emphasized. The use of teleological assessment and anthropomorphic description was discussed.

Metabolic integration during the host associations of multicellular animal endoparasites

Skeletal muscle fibers of the rat were studied with the electron microscope during the first stages of Trichinella spiralis infection. Severe changes in the fine structure caused by the larvae within the muscle fiber may be summarized as follows: 1) Increase of the sarcoplasmic matrix. 2) Fragmentation and lysis of the myofilaments. 3) Hyperplasia of the RS system. 4) Hyperplasia of the T system tubules which develop peculiar multitubular and multivesicular complexes. 5) Mitochondrial hyperplasia and hypertrophy. 6) Increase in number of the Golgi complexes. 7) Enlargement of and increase in number of the nuclei.

Jose Maria Rivera-Pomar

Papers

Biological significance of the early structural alterations in skeletal muscle fibers infected by Trichinella spiralis