Fig. 30.—A piece of pork heavily infected with pork measles (Cysticercus cellulosæ), natural size. (Stiles, Report U.S.A. Bureau of Agriculture, 1901.)
Fig. 31.—An isolated pork-measle bladder-worm (Cysticercus cellulosæ), with extended head, greatly enlarged. (Stiles, Report U.S.A. Bureau of Agriculture, 1901.)
Causation. The cause of cysticercus disease in the pig may be summed up in one phrase—viz., ingestion of eggs or embryos of Tænia solium.
Young animals alone seem to contract the disease. After the age of eight to ten months they appear almost entirely proof against it.
It is very rare in animals reared in confinement, but is relatively common in those roaming at liberty; because they are much more likely to discover human excrement and the embryos of tænia. The eggs having been swallowed, the six-hooked embryos are set at liberty in the intestine, perforate the tissues, enter the vessels, and are carried by the blood into all parts of the body. Those alone develop well which reach the interstitial and intermuscular connective tissue. The others in the viscera usually disappear. Their presence in the depths of the muscles produces slight general disturbance and signs of local irritation, due to the development of the cyst itself. At the end of a month the little vesicle is large enough to be visible to the naked eye; in forty to forty-five days it is as large as a mustard seed, and in two months as a grain of barley. Its commonest seats are the abdominal muscles, muscular portions of the diaphragm, the psoas, tongue, heart, the muscles of mastication, intercostal and cervical muscles, the adductors of the hind legs, and the pectorals.
Fig. 32.—Several portions of an adult pork-measle tapeworm (Tænia solium), natural size. (Stiles, Report U.S.A. Bureau of Agriculture, 1901.)
Symptoms. The symptoms of invasion are so little marked as usually to pass undetected. Occasionally, when large quantities have been ingested, signs of enteritis may occur, but these are generally ascribed to some entirely different cause. In some cases there is difficulty in moving, and the grunt may be altered.