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35-26: Trichinosis

Philip J. Rosenthal

ESSENTIALS OF DIAGNOSIS

ESSENTIALS OF DIAGNOSIS

  • Ingestion of inadequately cooked pork or game.

  • Transient intestinal symptoms followed by fever, myalgias, and periorbital edema.

  • Eosinophilia and elevated serum muscle enzymes.

GENERAL CONSIDERATIONS

Trichinosis (or trichinellosis) is caused worldwide by Trichinella spiralis and related Trichinella species. The disease is spread by ingestion of undercooked meat, most commonly pork, in areas where pigs feed on garbage. When infected raw meat is ingested, Trichinella larvae are freed from cyst walls by gastric acid and pass into the small intestine. The larvae then invade intestinal epithelial cells, develop into adults, and the adults release infective larvae. These parasites travel to skeletal muscle via the bloodstream. They invade muscle cells, enlarge, and form cysts (eFigure 35–43). These larvae may be viable for years. Pigs and other animals become infected by eating infected uncooked food scraps or other animals, such as rats.

eFigure 35–43.

Life cycle of Trichinella spiralis (trichina worm). Depending on the classification used, there are several species of Trichinella: T spiralis, T pseudospiralis, T nativa, T murelli, T nelsoni, T britovi, T papuae, and T zimbabwensis, all but the last of which have been implicated in human disease. Adult worms and encysted larvae develop within a single vertebrate host, and an infected animal serves as a definitive host and potential intermediate host. A second host is required to perpetuate the life cycle of Trichinella. The domestic cycle most often involves pigs and anthropophilic rodents, but other domestic animals such as horses can be involved. In the sylvatic cycle, the range of infected animals is great, but animals most often associated as sources of human infection are bear, moose, and wild boar. Trichinellosis is caused by the ingestion of undercooked meat containing encysted larvae (except for T pseudospiralis and T papuae, which do not encyst) of Trichinella species

image. After exposure to gastric acid and pepsin, the larvae are released from the cysts
image and invade the small bowel mucosa where they develop into adult worms
image. Females are 2.2 mm in length; males 1.2 mm. The life span in the small bowel is about 4 weeks. After 1 week, the females release larvae
image that migrate to striated muscles where they encyst
image. Diagnosis is usually made based on clinical symptoms and is confirmed by serology or identification of encysted or nonencysted larvae in biopsy or autopsy specimens. (From Global Health, Division of Parasitic Diseases and Malaria, CDC.)

A flowchart of the life cycle of Trichinella spiralis, or trichina worm.
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The worldwide incidence of trichinosis has decreased, but human infections continue to occur sporadically or in outbreaks, with estimates of ~10,000 cases annually. In addition to undercooked pork, infections have been transmitted by ingestion of game and other animals, including bear and walrus in North America and wild boar and horse in Europe. ...

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