Epidemiology and Etiology

T. spiralis is unusual in that a single individual animal serves as both intermediate and definitive (final) host, with the juvenile and adult worms located in different organs.

Humans acquire infections by ingesting infective juveniles, which are encysted in striated muscle of swine or other animals. The worms are freed from their cysts by gastric juices and invade the intestinal mucosa where they copulate. Males die shortly after copulation, and the females migrate through the intestinal epithelium, each giving birth to as many as 1,500 live young over a period of 4 to 16 weeks. Spent females eventually die and are absorbed by the host.

Young juveniles are carried throughout the body via the arterial system. They finally reach skeletal muscle, where they penetrate individual fibers and grow in a spiral fashion, eventually becoming encysted by a blunt, ellipsoidal capsule of host origin. The time required for complete encapsulation is about 3 months. Calcification of the capsule begins as early as 6 months and may take up to 2 years to complete. Eventually the worms also become calcified, although they may remain viable for several years prior to calcification.

Not all striated muscles are parasitized to the same degree. Among muscles most heavily affected are the diaphragm, tongue, and masticatory muscles, intercostals, and muscles of the arms and legs.

Most mammals are susceptible to Trichinella infections. Infections are maintained in nature by flesh-eating animals. Humans are regarded as accidental hosts because, barring cannibalism or the consumption of cadavers by other mammals, the infection reaches a dead end. Most human infections result from eating pork or pork products, but numerous fatal cases of trichinosis have been recorded from among those who eat undercooked or underfrozen bear or walrus meat.

Cooking meat is of importance in preventing trichinosis. Pork should be cooked until the pink color turns to gray. Alternatively, freezing of meat at -15°C for 20 days will destroy all parasites.

Pregnancy And Childbirth

Pregnancy And Childbirth

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