Distribution of Trichinella spiralis in Muscles of Experimentally Infected Swine

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Abstract
Ten 3-month-old pigs each were fed 50,000 Trichinella spiralis larvae; one was fed 100,000 and another one, 150,000 larvae; none developed any sign of disease. The degree of infection produced in the muscles of these animals, without accompanying evidence of clinical trichinosis, is much higher than has been previously reported. From one pig fed 50,000 decapsulated larvae, 10,841,800 larvae were recovered by digestion of 9,536 g of dissected muscle (average, 1,137 larvae per gram of muscle), a yield 216 times the infecting dose. From a second pig fed 50,000 excysted larvae, 7,820,000 were recovered by digestion of 10,000 g of dissected muscle (average, 782 larvae per gram of muscle), a yield 156 times the infecting dose. The most heavily infected muscle was the diaphragm in 7 of 12 pigs and the tongue in five animals. In one pig fed 50,000 larvae, the larval count was 3,840 per gram of diaphragm. A wide variation was found in the degree of infection among pigs ingesting the same number of larvae. Of nine skeletal muscles examined (exclusive of the diaphragm, tongue, and masseters), the deltoid muscles and then the pectoral muscles usually had the highest concentrations of larvae. While the number of cysts in individual histologic sections of a random sample of a given muscle is not a reliable index of the degree of infection of that muscle, the number of cysts counted in a field of 80 mm2 usually approximated the number of larvae recovered by digestion in 0.05 g of that muscle.