Clinical Pearls & Morning Reports
Published October 3, 2018
Trichinosis is a foodborne parasitic infection caused by roundworms of the genus trichinella. It is associated with consumption of improperly cooked meat that contains infective larvae. Read the latest NEJM Clinical Problem-Solving article here.
Q: How common is trichinosis in the United States?
A: Trichinosis is a rare disease in the United States, with typically fewer than 50 cases diagnosed each year. Improved animal husbandry practices have led to a dramatic decrease in the incidence of trichinosis from commercially raised pork.
Q: What are the most important risk factors for trichinosis in the United States and elsewhere?
A: Consumption of wild game or raw meat and travel to endemic areas are now the most important risk factors, with bear meat and noncommercially raised swine being the most common sources of infection in the United States. A disproportionate number of cases are seen in patients of Asian descent. Cultural and regional dietary preferences that feature raw meat can lead to trichinosis outbreaks. Laab (or larb) is a traditional dish of northern Thailand and Laos that is often made with raw pork and has been associated with outbreaks of trichinosis. Among travelers, consumption of regional delicacies such as raw horse meat in France and Italy, wild boar in Southeast Asia, and dog meat in China and Korea has led to trichinosis.
A: Trichinosis is a biphasic illness, with an initial enteral phase followed by a parenteral phase. In the enteral phase, larvae invade small-intestine mucosa, mature into adult worms, and produce larvae; after an incubation period of 1 to 2 days, patients typically present with symptoms of nausea, vomiting, watery diarrhea, and abdominal pain, which can last up to 3 to 4 weeks. The classic and most severe symptoms of trichinosis are seen during the parenteral phase, when newborn larvae enter the lymphatic and blood vessels, disseminating to skeletal muscle and other organs. This phase typically begins 2 weeks after ingestion and can last up to 8 weeks as adult worms in the small intestine produce more larvae. Migrating larvae cause direct physical damage to the tissues and trigger an immune response. Typical symptoms and signs include fever, myalgia, weakness, headache, periorbital edema, rash, eosinophilia, and elevated levels of muscle enzymes. Although trichinella does not migrate through lung tissue, respiratory symptoms are common. Chest and respiratory symptoms may be related to larval invasion of chest and myocardial muscle or a pulmonary reaction to larvae passing through the pulmonary circulation.
A: Laboratory confirmation of the diagnosis depends on detection of the trichinella antibody in serum. Evidence of trichinella larvae on muscle biopsy specimens is rarely needed because clinical history and laboratory data, including results from serologic testing, are usually adequate to establish the diagnosis. Treatment eliminates the adult worms from the intestine, prevents production of new larvae, and eliminates larvae in lymphatic and blood vessels. Early diagnosis and treatment can reduce the burden of muscle invasion and disease severity. Delayed diagnosis and treatment are problematic because anthelmintic drugs may be less effective once larvae enter striated muscle.