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Other Helminth Infections: Trichinella spiralis and Flukes
Trichinosis
The most common Trichinella species in the United States is Trichinella spiralis, which is almost worldwide in its distribution. However, other Trichinella species infect humans in Africa and in the arctic regions. Humans become infected by eating undercooked pork meat. The main reservoir is the pig.
The life cycle of Trichinella has an intestinal phase and a muscular phase. When the uncooked meat is eaten, larvae are released in the small intestine, where they go through four phases of development to adulthood. After approximately 1 week, the adult female worms produce larvae which cross the intestinal wall, spread via blood vessels, and settle in the striated muscle. A single worm may produce as many as 1500 larvae. The second-generation larvae can survive in the host for many years. In the United States the number of trichinosis cases reported each year is usually less than 50.
Clinical Picture
During the initial stage of trichinosis, a patient may have mild gastroenteritis with nausea, vomiting, or abdominal pain, and diarrhea. This phase may last up to 1 week. When the larvae enter the muscle, myalgia, fever, periorbital edema, and systemic signs of allergic response develop. The more larvae present, the more severe will be the disease. Generalized edema may develop, and proteinuria can follow. Central nervous system signs and symptoms, cardiomyopathy, and extraocular muscle involvement occur in patients with moderate to severe infection.
Muscle tenderness can be readily detected, along with an unusually high white blood cell count, increased level of immunoglobulin E, muscle enzymes (creatinine kinase and lactate dehydrogenase) and significant eosinophilia. In pregnant women, Trichinella infection can cause abortion or premature delivery.
Diagnosis
The diagnosis of trichinosis is made by obtaining muscle tissue and demonstrating the parasitic complexes. The diagnosis can also be made by detecting Trichinella -specific DNA using polymerase chain reaction. After approximately 2 weeks, enzyme-linked immunosorbent assay can detect the antibodies in some patients.
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