Types of myofibers parasitized in experimentally induced infections with Sarcocystis cruzi and Sarcocystis capracanis.

Eighteen calves were orally inoculated with either 200,000 or 225,000 sporocysts of Sarcocystis cruzi. Eight goats were orally inoculated with 20,000 sporocysts of S capracanis. Calves and goats were euthanatized at various times after inoculation, and portions of their right and left biceps femoris, right and left longissimus dorsi, myocardium, and tongue were frozen at -150 C in precooled isopentane and stored at -70 C. Frozen sections of these muscles were stained with hematoxylin and eosin, modified Gomori's trichrome, nonspecific esterase, diphosphopyridine nucleotide tetrazolium reductase, and adenosinetriphosphatase at pH 10.4 and 4.6. Muscle from the same locations was fixed in 10% neutral buffered formalin, processed for paraffin embedding, sectioned, and stained with hematoxylin and eosin. Microscopic examination of both calf and goat tissue indicated that both type I and type II muscle fibers were equally infected and that infected myofibers showed no apparent damage other than displacement by sarcocysts. Occasionally, muscle fibers within the muscle spindles contained sarcocysts.