Atlas of livestock parasites
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Trichinella spiralis



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Trichinella spiralis
Trichina worm

General Description:
Adult trichina worms are tiny nematodes 2 to 4 mm long.

Life Cycle:
The female worm in the small intestine produces huge numbers of active larvae, which penetrate the intestinal wall and travel via the lymph to the blood vessels. After several weeks in the circulation, the larvae leave the capillaries and encyst in muscle tissue, remaining viable for years. Further development occurs only if the infected tissue is eaten by another host, often a rat, man, or pig. Swine therefore may be both intermediate and principal hosts for trichina worms. Within a few hours after ingestion, larvae are freed by digestion of the cysts and mature in several days. After the worms copulate in the intestine, the females penetrate the mucosa, where they produce larvae for 2 weeks.

Small intestine.

Geographical Distribution:

While not particularly damaging to swine in most cases, infected carcasses may be condemned. Trichinosis in hu-mans may cause severe or even fatal damage.

Effect on Host:
Trichinella is much less pathogenic in swine than in man. The larvae have a predilection for the diaphragm and jaw muscles in pigs. In man, intestinal adult worms cause nausea, diarrhea, and abdominal pain. Larvae burrowing into muscles produce stiffness and pain. Death may occur 4 to 6 weeks after human infection and is usually caused by paralysis of respiratory muscles.

Diagnostic Information:
At necropsy, larvae may be found in biopsied muscle specimens of infected carcasses by microscopic examination.


To prevent infection of swine, garbage must be cooked thoroughly before being fed to pigs and rat infestation of the facilities should be controlled. Human infection can be controlled by thorough cooking or freezing of pork before consumption. The meat of game animals also should be prepared so that all Trichinella are killed.


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