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Pathology => Human Diseases => Trichinosis
Trichinosis
INTRODUCTION
Trichinosis, common name applied to a disease of rats, swine, bears, cats, dogs, and humans, caused by infection with the larvae of a parasitic nematode worm, the trichina worm, Trichinella spiralis. The minute trichina worm is almost worldwide in distribution.
INFECTION OF ANIMALS
Animals are infected with trichinosis by eating flesh in which the larvae of the trichina worm are encysted. The larvae are freed from their cysts by the digestive juices of their host's intestine; two days after entering the intestinal tract, they become adults and mate. The females burrow into the lining of the intestine and, after six days, begin to bear numerous larvae. Seven days after the encysted larvae have been ingested by the host, the newly born larvae migrate into the lymph channels of the intestine, from which they enter the bloodstream.
From the blood the larvae penetrate the striated, or voluntary, muscles about 14 days after birth. Within these muscles the larvae mature until they are 16 days old; they then cease developing and form a capsule about themselves from the sheath, or sarcolemma, of the host's skeletal muscle. The host secretes lime salts that are deposited in the capsule, eventually transforming the capsule into a completely calcified cyst.
TRANSMISSION TO HUMANS
Trichinosis is most often contracted in humans by eating infected pork. Despite rigid standards of meat inspection in the U.S., infected pork can sometimes pass inspection because the disease is extremely difficult to recognize. Trichina cysts in pork may be destroyed completely by freezing the meat at -15° C (+5° F) for 21 days or -30° C (-22° F) for about 25 hours. Trichina larvae that are not encysted are destroyed when the meat is heated to 66° C (150° F). Ordinary curing and smoking processes do not render pork safe for consumption.
During the stage of infection, after the immature trichina worms are freed from their cysts, the maturing larvae cause severe irritation of the intestinal tract. Symptoms of infection include abdominal pain, nausea, vomiting, and watery stools. With the release, or migration, of the larvae into the bloodstream, the face very often becomes puffy and swollen, especially around the eyes, and headache and even delirium occur; the heart muscles also are often damaged. The invasion stage is marked by muscle spasms and pains in the joints. People with trichinosis usually recover in about six months, after the mature larvae become encysted.
EFFECTS AND TREATMENT
Some persons recovering from trichinosis suffer permanent heart or eye damage, and about 5 percent of cases are fatal. Because of the difficulty of diagnosis in its early stage, the disease is rarely treated then. Drug treatment of trichinosis with thiabendazole appears to be effective in humans during the intestinal phase but may not be effective against larvae that have already migrated.
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