para>ransplacental passage of migrating larvae is possible; elevated progesterone during pregnancy is helminthotoxic to newborn larvae, leading to a milder infection. Trichinellosis can cause miscarriage or premature delivery. Mebendazole and albendazole are contraindicated in pregnancy.
EPIDEMIOLOGY
Incidence
- Only 15 cases were reported in the United States in 2011 (7)[C] and 12 cases in 2012 (1).
- Worldwide from 1986 to 2009, there were ~65,000 cases and 42 deaths (8)[C].
- Higher incidence in Alaska and Northeastern United States
- Autopsy studies suggest that most mild cases are probably undiagnosed.
- Predominant age: 20 to 49 years, although cases were reported from all age groups.
- Predominant sex: male = female
ETIOLOGY AND PATHOPHYSIOLOGY
Eating undercooked meat contaminated with viable Trichinella cysts. Symptoms and severity relate to how many larvae are ingested and cyst burden.
- Enteral phase (phase I)
- Cysts are broken down by digestive acid in the stomach, releasing larvae, which develop into mature adult worms in the small intestine.
- ~1 week after ingestion; may last 3 to 5 weeks
- Symptoms result from presence of cyst and worms.
- Muscular phase (phase II)
- Female worms release newborn larvae that migrate through blood vessels and lymphatics to multiple organ systems.
- 2 to 3 weeks after ingestion; may last for 2 months
- Larvae encyst in striated skeletal and cardiac muscle forming a "nurse cell " that nourishes and protects the organism from host immunity.
- IM cysts usually calcify over time.
- Cyst can survive in humans up to 30 years.
- Symptoms result from invasion of larvae/worms and the resulting inflammatory process leading to edema, vasculitis, and intravascular thrombi.
- Symptoms depend on location of larvae/worms.
RISK FACTORS
- Access to wild game, homemade pork products, or noncommercial sources of meat
- Eating pigs fed on uncooked garbage
- Consuming undercooked pork
- Eating inadequately cooked or frozen wild game
- Ethnic groups from Southeast Asia who raise their own pork or consume partially cooked pork products
- Residents in Alaska and Northeastern United States
- Risk for more severe symptoms (9)[C]:
- >10 years old
- Leukocytosis
- High eosinophil count
- Repeated consumption of contaminated meat
GENERAL PREVENTION
- Avoid consumption of undercooked pork or game.
- Prolonged freezing may help prevent disease (less so for wild game meat).
DIAGNOSIS
Diagnosis is based on symptoms consistent with trichinellosis and confirmatory labs in the setting of appropriate exposure to pork or wild game.
HISTORY
Consumption of undercooked pork or wild game, followed with a week by symptoms:
- Common: fever, abdominal cramping, diarrhea, myalgias, edema
- Less common: eye complaints, headache, cough, shortness of breath, mental status changes
PHYSICAL EXAM
- Signs and symptoms begin within 1 week of ingesting infected meat.
- Common findings: phase I and phase II
- Diarrhea
- Abdominal cramping
- Fever
- Myalgias
- Periorbital edema
- Weakness
- Less common findings: phase II
- Conjunctivitis
- Subconjunctival hemorrhage
- Retinal hemorrhages
- Maculopapular rash
- Splinter hemorrhages
- Headache
- Photophobia
- Pneumonitis
- Tachycardia
- Heart failure
- Pericardial effusion
- CNS involvement, possible encephalitis
- Clinical findings depend on number of ingested infective larvae and phase of parasitic invasion:
- Light infections: <10 larvae per gram of muscle; usually asymptomatic
- Heavy infections: >50 larvae per gram of muscle; can be life-threatening
- Gastrocnemius, masseter, diaphragm, biceps, lower back, extraocular muscles, jaw, and neck are the most frequent site of skeletal muscle symptoms due to larval migration; in severe cases, myocardial damage, pulmonary infiltration, and focal neurologic damage can occur. Clinical findings correlate with affected musculature.
- Myocarditis occurs in 5 " 20% of cases; from infiltrate of eosinophils and mononuclear cells, rather than larvae in the myocardium (10)[C]
DIFFERENTIAL DIAGNOSIS
- Acute rheumatic fever
- Arthritis
- Angioedema
- Botulism
- Collagen vascular disease
- Dermatomyositis
- Encephalitis
- Eosinophilia-myalgia syndrome
- Gastroenteritis
- Idiopathic hypereosinophilic syndrome
- Idiopathic polymyositis
- Influenza
- Meningitis
- Pneumonitis
- Polyarteritis nodosa
- Polymyositis
- Typhoid fever
- Tuberculosis
DIAGNOSTIC TESTS & INTERPRETATION
- Antibody levels:
- Often not detectable for 3 to 5 weeks
- High (15 " 22% ) false-negative rate in phase I
- Peak 3rd month
- Remain detectable 2 to 3 years
- Paired specimens are helpful, 1 to 2 months apart; look for 4-fold increase in titer.
- Serologic tests for T. spiralis, IgM/IgG (10,11)[C]
- ELISA for IgM and IgG
- Bentonite flocculation after 3rd week for parasite-specific antibody
- DNA testing: random amplified polymorphic DNA, polymerase chain reaction (PCR)
- Excretory/secretory (ES) antigen (in vitro)
- A 3,6-dideoxyhexose sugar (tyvelose), a highly specific immunodominant epitope (11)[C]
- Nonspecific labs:
- Increased total IgE levels (11)[C]
- Eosinophilia (>600/mm3) with leukocytosis
- Increased creatine phosphate kinase
- Increased lactate dehydrogenase
- Hypergammaglobulinemia
- Elevated ESR (several weeks)
- Urinalysis may show myoglobinuria, proteinuria
- Drugs that may alter lab results: Thiabendazole may increase serum glutamic-oxaloacetic transaminase.
- Radiology studies
- CT scan (visualize calcified muscle cysts)
- MRI for evaluation of neurologic complications
- Chest x-ray (CXR) may detect patchy infiltrates
- Extremity radiograph may show calcified densities.
Diagnostic Procedures/Other
Muscle biopsy of gastrocnemius or deltoid with ≥1 g of muscle, examine between compressed slides using microscopy (higher detection rate, diagnostically definitive)
Test Interpretation
Larvae on muscle biopsy is confirmative; absence of larvae on biopsy does not exclude diagnosis; rarely able to find retrieved worms from stool specimens
TREATMENT
GENERAL MEASURES
- Outpatient unless complications (cardiac, pulmonary, or neurologic)
- CDC for appropriate diagnostic tests: (404) 639-3311
- http://www.cdc.gov/parasites/trichinellosis/gen_info/faqs.html
- Bed rest, antipyretics, analgesics
MEDICATION
First Line
- For early intestinal phase (first 1 to 2 weeks) to treat adult worms:
- Mebendazole: adults and children >2 years of age: 200 to 400 mg TID for 3 days, then 400 to 500 mg TID for 10 days (10)[C]
- Albendazole: adults and children >2 years of age: 400 mg BID for 10 to 14 days (10)[C]
- Pyrantel single dose of 10 to 20 mg/kg of body weight, repeated 2 to 3 days for pregnant women and children (10)[C]
- No drugs are as effective against larvae once they are encysted in muscle. Treatment may limit further dissemination.
- CDC for current recommendations: (404) 639-3311.
- Severe cases: corticosteroids- prednisone, 40 to 60 mg/day for 3 to 5 days; taper as symptoms subside, used to decrease inflammation when signs of myocarditis, neurologic disease, pulmonary insufficiency, or severe myositis appear.
- Analgesics, NSAIDs, and antipyretics as needed
- Contraindications: Corticosteroids are contraindicated in the intestinal phase because they may prolong the phase.
- Precautions: Limited experience exists with the use of medications in small children and in pregnancy. Mebendazole and albendazole should not be given in pregnancy and are not recommended in children <2 years of age.
- Significant possible interactions:
- Carbamazepine or alcohol may decrease the effect of mebendazole.
- Cimetidine may increase the level of mebendazole.
Second Line
Thiabendazole: once drug of choice; replaced by the drugs previously mentioned because they have fewer side effects and are equally effective
SURGERY/OTHER PROCEDURES
Pacemaker insertion has been required for severe myocarditis.
INPATIENT CONSIDERATIONS
Admission Criteria/Initial Stabilization
- Admit for cardiac, pulmonary, or neurologic manifestations.
- Pregnancy
ONGOING CARE
FOLLOW-UP RECOMMENDATIONS
Activity:
- As tolerated
- Bed rest may help muscular pain.
Patient Monitoring
- Monitor for cardiac, neurologic, and pulmonary complications.
- Long courses of treatment with mebendazole or albendazole may cause bone marrow suppression. Follow complete blood counts and discontinue medication if adverse side effects occur.
DIET
Avoid undercooked pork and game meat.
PATIENT EDUCATION
- Cook potentially contaminated meat, such as pork, to minimum internal temperature of 160 °F (71 °C).
- Freeze at ’ 15 °C for 21 days (longer if meat >15 cm thick); however, Trichinella larvae in wild game may be resistant to freezing.
- Do not feed hogs uncooked garbage.
- CDC: http://www.cdc.gov/parasites/trichinellosis/
- USDA Fact Sheets: Jerky and Food Safety
- http://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/meat-preparation/jerky-and-food-safety/CT_Index
PROGNOSIS
- Most infections are asymptomatic, short-lived, and have an uneventful recovery without medication.
- Prognosis is good in most cases, although 5 " 10% of the cases can be severe.
- No clear evidence that chronic trichinosis exists.
- <1% of cases can be fatal, generally around 4th to 8th week, as a result of cardiac failure or pneumonia.
- Treatment is most effective early in course, but it is difficult to diagnose trichinosis early (10)[C].
COMPLICATIONS
- Meningitis; subcortical infarcts, encephalitis
- Myocarditis with congestive heart failure
- Glomerulonephritis
- Sinusitis
- Pneumonitis; pneumonia
- Pregnancy: abortion, premature delivery
- Death: typically cardiac or thromboembolic events
REFERENCES
11 Adams DA, Jajosky RA, Ajani U, et al. Summary of notifiable diseases " United States, 2012. MMWR Morb Mortal Wkly Rep. 2014;61(53):1 " 121.22 Neghina R, Neghina AM, Marincu I, et al. Reviews on trichinellosis (I): renal involvement. Foodborne Pathog Dis. 2011;8(2):179 " 188.33 Moscatelli G, Sordelli N, Moroni S, et al. Neurotrichinosis in a pediatric patient. Pediatr Infect Dis J. 2014;33(1):115 " 117.44 Neghina R, Neghina AM, Marincu I, et al. Reviews on trichinellosis (II): neurological involvement. Foodborne Pathog Dis. 2011;8(5):579 " 585.55 Neghina R, Neghina AM, Marincu I. Reviews on trichinellosis (III): cardiovascular involvement. Foodborne Pathog Dis. 2011;8(8):853 " 860.66 Neghina R, Neghina AM. Reviews on trichinellosis (IV): hepatic involvement. Foodborne Pathog Dis. 2011;8(9):943 " 948.77 Adams DA, Gallagher KM, Jajosky RA, et al. Summary of notifiable diseases " United States, 2011. MMWR Morb Mortal Wkly Rep. 2013;60(53):1 " 117.88 Murrell KD, Pozio E. Worldwide occurrence and impact of human trichinellosis, 1986-2009. Emerg Infect Dis. 2011;17(12):2194 " 2202.99 B lescu A, Nemet C, Zamfir C, et al. Identifying risk factors for symptoms of severe trichinellosis " a case study of 143 infected persons in Brasov, Romania 2001-2008. Vet Parasitol. 2013;194(2 " 4):142 " 144.1010 Gottstein B, Pozio E, N Άckler K. Epidemiology, diagnosis, treatment, and control of trichinellosis. Clin Microbiol Rev. 2009;22(1):127 " 145.1111 Dupouy-Camet J, Bruschi F. Management and diagnosis of human trichinellosis. In Dupouy-Camet J, Murrell KD, eds. FAO/WHO/OIE Guidelines for the Surveillance, Management, Prevention and Control Trichinellosis. 1st ed. Paris, France: World Organization for Animal Health Press; 2007:37 " 68.
CODES
ICD10
B75 Trichinellosis
ICD9
124 Trichinosis
SNOMED
- Infection by larvae of Trichinella spiralis (disorder)
- invasive trichinosis (disorder)
- trichinosis myositis (disorder)
CLINICAL PEARLS
- The most common sources of trichinellosis in the United States is wild bear meat. Worldwide, pork is the most common source.
- Hallmark signs and symptoms of trichinellosis are periorbital edema, myositis, and eosinophilia.
- Trichinellosis generally is self-limited. Specific therapy generally is not needed unless there are complications.
- ELISA is the most sensitive serologic test to confirm trichinellosis.
- To increase the yield of muscle biopsy, compress specimen between two microscope slides (trichinelloscopy) to look for larvae. Yield is also highest near tendinous insertions.