Myxobolus sp. can cause in vivo myoliquefaction in the host Paralichthys orbignyanus (Osteichthyes, Paralichthydae).

We found intense myoliquefaction in vivo among specimens of wild and farmed South American flatfish Paralichthys orbignyanus Valenciennes, 1839. The soft flesh condition was attributed to Myxobolus sp. since the fish were not infected by myxosporeans which are usually associated with this condition (Kudoa spp.), and other causes (bacteria, fungi) were not found. The histopathology of the infection is described.

[The ultrastructural changes of Sarcocystis ovifelis infested sheep tongue myofibrils].

Structural changes were observed in filaments of Sarcocystis ovifelis infected sheep tongue myofibrils. In sarcocysts containing myofibrils, actin filaments and Z-disks, myosin filaments and M-line were seen destroyed. Protein bridges, uniting actin and myosin filaments into a joint complex (net), eventually become not visible, and as a result separate Z-disks and free filaments appear. Fibrils, referred to as leptomeric, have been first revealed between protrusions of the sarcocyst surface apparatus. These are striated filaments with periodic 100 nm striation of dark and light bands, made of thin and short 120-200 nm long filaments 5 nm in diameter. The genesis of leptomeric fibrils still remains obscure. In sarcocysts infected myofibrils these may be involved in metabolite transportation to the intercellular space and back.

Adaptive changes in muscle fibers infected with Trichinella spiralis.

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.