Barbara S. Giesser, MD
DESCRIPTION 
Trichinosis is the systemic illness that results from infestation with larvae of the nematode worm Trichinella sp. It may consist of general, gastrointestinal, neurological, cardiac, and respiratory manifestations.
EPIDEMIOLOGY
- Incidence in the US has been declining over the past 50 years.
- Currently, cases in the US occur in average <40 years of age.
- May be acquired by traveling in foreign countries.
RISK FACTORS
- Consumption of undercooked pork or wild game such as deer, bear, horse meat, or crocodile which contain larvae of Trichinella sp.
GENERAL PREVENTION
- Recommendations are to cook pork and game meats until well done (not pink), to reach internal temperatures of at least 71°C (160°F) for at least 1 minute
- Appropriate farming methods of pigs
- Appropriate freezing and curing methods to render at-risk meat safe.
Pregnancy Considerations
- There are reports of trichinosis being transmitted in utero from mother to fetus.
- Maternal trichinosis has been associated with spontaneous abortion. Lactation has been reported to be suppressed in postpartum women with trichinosis.
ETIOLOGY
- Invasion of tissue by worm larvae
PATHOPHYSIOLOGY
- Inflammatory response to infection
- Parasite promotes Th2 cytokine shift in host
- After the ingested cyst wall is digested in the stomach, the larvae are released and enter the general circulation from the gut. Although they may invade multiple organ systems, they encyst in striated muscle and may persist there for many years. An allergic vasculitis may occur and is responsible for edema and hemorrhage.
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HISTORY
- The diagnosis is suggested by the symptom complex of fever, malaise, diarrhea, abdominal pain myalgia, and periorbital edema.
- History of ingesting undercooked pork or game
- The incubation period for the appearance of generalized symptoms from time of ingestion varies from approximately 1 day to 7 weeks, with earlier appearance of symptoms generally presaging a more severe course.
PHYSICAL EXAM
- Fever, malaise
- Cramping, diarrhea
- Periorbital edema
- Subconjunctival hemorrhages
- Myocarditis
- Maculopapular rash
- Myalgia
- Muscles painful to palpation
- Pain occurring at rest but worse with movement
- Limbs, extraocular muscles, tongue, respiratory, neck muscles
- Weakness and stiffness in affected muscles
- CNS involvement occurs in 10–20% of cases and may result from direct invasion of tissue by larvae, obstruction of blood vessels by larvae, toxic vasculitis, or acute host hypersensitivity reaction. In untreated patients with neurological manifestations, mortality may be as high as 50%.
- Headache
- Seizures
- Meningitis/encephalitis
- Cerebrovascular thrombosis/infarction
- Tinnitus/decreased hearing
- Diplopia, facial paresis
- Polyradiculoneuritis
DIAGNOSTIC TESTS AND INTERPRETATION
Lab
Blood tests
Imaging
Neuroimaging may reveal focal areas of infarction, hemorrhage, or thrombosis and in cases where there has been larval invasion of the brain. In some cases, larvae may be found in spun samples of CSF. In cases of pulmonary complications, there may be pneumonia or pleural effusion present on chest x-ray film. MRI of skeletal muscles may show cysts but has not been assessed as a diagnostic test for this indication.
Diagnostic Procedures/Other
- The definitive test for trichinosis is the presence of Trichinella sp. larvae in muscle biopsy of the affected individual. Biopsy may be positive as early as 2 weeks after infection. Serologic tests may become positive 2–8 weeks after initial infection.
- ECG
DIFFERENTIAL DIAGNOSIS
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MEDICATION
- Intestinal phase
- Mebendazole (Vermox®) 200–400 mg PO t.i.d. for 3 days, followed by 400–500 mg PO t.i.d. for 10 days
- Albendazole (Zentel®) 400 mg b.i.d. for 8–14 days
- Pyrantel (Combantrin®) may be used in pregnant women and young children at doses of 10–20 mg/kg/day for 2–3 days but only affects intestinal nematodes and not muscle larvae.
- Corticosteroids 0.5–2.0 mg/kg/day in divided doses for 4–10 days
- Repletion of proteins and electrolytes
- Contraindications: Albendazole and mebendazole are contraindicated for use in pregnant women and not recommended for use in children less than 2 years of age.
- Precautions
- Side effects include neutropenia, abnormal liver function tests, myalgia, and fatigue.
- In patients who develop allergic vasculitis or hypersensitivity reactions, steroids may be combined with antihelminthic treatment.
ADDITIONAL TREATMENT
General Measures
Other than specific treatment of complications, therapy is directed at stopping infection and eradicating the parasite within the host (vide supra). Management of complications is symptom specific, e.g., anticonvulsant therapy for seizures. Corticosteroids may be indicated in moderate-to-severe cases of allergic vasculitis, e.g., prednisone at doses of 60–120 mg/day or higher if needed. Steroids should not be used without concomitant administration of antihelminthics in early cases (<6 weeks after ingestion) because they may prolong the presence of adult worms in the gut.
- Symptomatic treatment
- Symptomatic therapy is aimed at specific complications. Fluids may be needed for dehydration or diuretics in cases of severe edema. Antiarrhythmics may be indicated in cases of cardiac complications. Rarely, with severe pulmonary involvement, assisted ventilation may be necessary. Myalgia may respond to conventional doses of salicylates or nonsteroidal antiinflammatory drugs. After the acute phase, physical or occupational therapy may be indicated to restore function in affected muscle.
COMPLEMENTARY AND ALTERNATIVE THERAPIES
N/A
IN-PATIENT CONSIDERATIONS
Admission Criteria
Patients with moderate or severe trichinosis need to be admitted primarily for the management of systemic manifestations and complications, e.g., dehydration or cardiopulmonary or CNS manifestations. The most common cause of death in trichinosis is myocarditis/cardiac failure, which most frequently occurs in weeks 4–8 of infection.
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FOLLOW-UP RECOMMENDATIONS
Patient Monitoring
Patients should be monitored in the first few weeks of the illness for the development of neurological, cardiac, pulmonary, and respiratory complications. Patients may develop hypersensitivity reactions (Jarisch–Herxheimer reaction) as the result of larval death due to antihelminthic therapy.
PATIENT EDUCATION
Patients should be warned against eating raw or undercooked pork or wild game products, particularly when traveling abroad. They should be instructed in proper cooking and freezing procedures when home processing pork and game products.
PROGNOSIS
- Recovery is complete in 2–6 months in most cases.
- Encysted larvae in muscle may persist for up to decades and be asymptomatic.
- Rarely, there is a chronic syndrome that consists primarily of fatigue and myalgia.
- May have up to 5% mortality.
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