Basics
Description
- Infection caused by ingestion of undercooked meat containing nematode (roundworm) larval cysts of the Trichinella genus
- Clinical disease in humans characterized by an intestinal phase followed by a muscular phase
- Extremely wide host range and geographic distribution
Epidemiology
- Historically, most U.S. infections are due to Trichinella spiralis in commercial pork.
- Currently, more U.S. infections are associated with wild game meat (especially bear) or through spillover to domestic animals.
- Occasional grouped outbreaks (e.g., families and communities with common exposure)
- Reservoir hosts include rodents, domesticated animals (e.g., dogs, cats), raccoons, opossums, and skunks.
Incidence
- Estimated 10,000 cases per year worldwide, with a mortality rate of 0.2% in main 55 countries reporting
- Between 2002 and 2007 in the United States, average of 11 cases annually
- Decreasing reported case numbers attributed to decline in prevalence of Trichinella in commercial swine (1.41% in 1900, 0.125% in 1966, and 0.013% in 1995), federal regulation preventing uncooked meat consumption by commercial swine, and increased public awareness regarding proper meat handling and preparation
- Likely underreported, particularly in developing countries with modest health controls
Prevalence
- ’ Ό4% of cadavers in 1970 study with evidence of previous infection (additional estimates range from 10 to 20% prevalence)
Risk Factors
- Consumption of inadequately cooked meat, even in small quantities
- Consumption of foreign meat (e.g., horse in France, dog in China) or wild game (e.g., bear, cougar, hyena, lion, panther, fox, horse, seal, walrus)
- Exposure to adulterated food (e.g., pork mixed in beef product)
- Traveling to underdeveloped countries
- Compromised immune status of host
General Prevention
- Consume only fully cooked meat, pork, and wild game; meat should reach >145 °F internally, no pink color
- Freezing kills T. spiralis in pork (<6 inches thick) at ’ 20 °F for 6 days, ’ 10 °F for 10 days, and ’ 5 °F for 20 days.
- Freezing may not kill other Trichinella species, particularly in wild game.
- Curing, smoking, salting, and drying meat (including jerky) are not reliable sterilization methods.
- Routinely clean meat processing equipment.
- Irradiation may not kill Trichinella but should prevent replication.
- Avoid feeding swine uncooked meat scraps.
- Actively control reservoir hosts (e.g., rodents).
Pathophysiology
- Trichinella are obligate intracellular parasites capable of infecting warm-blooded animals
- At least 8 Trichinella species identified: Trichinella spiralis (most common), Trichinella britovi, Trichinella pseudospiralis, Trichinella papuae, Trichinella nativa, Trichinella nelsoni, Trichinella murrelli, and Trichinella zimbabwensis
- Life cycle of all species comprises 2 generations in the same host (broad range of species " mammal, birds, and reptiles), but only humans become clinically affected.
- Disease not transmissible person to person
- Larvae in undercooked meat eaten by the patient are released after cyst wall digestion by gastric enzymes, pass to the small intestine, invade mucosa, then develop into adult worms.
- Incubation period is 1 " 2 weeks.
- Fertilized females release larvae ( ’ Ό500) over 2 " 3 weeks; adult worms do not multiply in human host and are expelled in feces.
- Newborn larvae travel the bloodstream to seed skeletal muscles, where they grow 10-fold, coil, encyst, and cause muscle fibers to enlarge and become edematous. Nonskeletal muscle may have granulomatous reactions, but larvae are found only in skeletal muscle.
- Cysts (hyaline capsules) may calcify over several months to years.
- Growing body of research on the ability of parasites to modulate the immune system and implications of this for immune-mediated diseases
Etiology
T. spiralis is the organism that causes trichinosis and is acquired by the consumption of raw or undercooked, infected meat.
Commonly Associated Conditions
- Rheumatic syndromes: polyarteritis nodosa " like systemic necrotizing vasculitis, symmetric polyarteritis, glomerulonephritis
- Immunocompromised hosts are at risk for more serious or prolonged infection.
Diagnosis
History
- Ingestion of inadequately cooked meat (commercial and noncommercial pork, game animals, foreign meat)
- Others with similar symptoms and same dietary exposure
- Signs and symptoms
- Clinical severity varies, from asymptomatic (most common) to fatal (rare); depends on Trichinella species and inoculum size
- Children often have fewer and milder symptoms than adults.
- Many signs and symptoms (i.e., periorbital and muscle edema, eosinophilia) due to allergic reaction to parasite antigens
- Nonspecific signs and symptoms may mimic other illnesses
- Enteral phase (24 hours " 7 days after infection): symptoms due to intestinal ulceration from mucosal invasion by adult worms
- Diarrhea, abdominal pain, nausea, vomiting, anorexia
- May persist for weeks
- Parenteral phase (1 " 8 weeks after infection): symptoms due to systemic invasion
- General: fever (begins at 2 weeks, peaks after 4 weeks, night spikes to 40 " 41 °C), weakness, malaise, myalgias
- Ocular: periorbital edema, subconjunctival hemorrhage, conjunctivitis, disturbed vision, ocular pain, chemosis
- Muscular: myalgias, myositis (usually in extraocular muscles, then masseters, tongue, neck, limb flexors, lumbar muscles, intercostals, and diaphragm) with dyspnea, cough, hoarseness
- Neurologic: headache, focal paralysis, delirium, psychosis
- Skin: urticarial rash, subungual hemorrhages
- Parenteral phase symptoms typically peak 2 " 3 weeks after infection.
- Malaise and weakness may persist for weeks.
- Cardiac: myocarditis, arrhythmias secondary to myocarditis
- Convalescent phase (begins 2nd month, may last months to years): myalgias, weakness
Physical Exam
Fever, periorbital and generalized edema, muscular tenderness, urticaria, plus findings related to neurologic or cardiac involvement mentioned in "History " section
Diagnostic Tests & Interpretation
Lab
- Stool ova and parasite examination
- CBC and differential: leukocytosis (moderate) with eosinophilia (up to 70%, peaks 10 " 21 days postinoculation but prior to clinical symptoms)
- Elevation of muscle enzymes (lactate dehydrogenase [LDH], creatinine phosphokinase [CPK], aldolase)
- Specific anti-Trichinella antibody detection
- Serologic tests are available through the U.S. Centers for Disease Control and Prevention or state and some private labs.
- Detection of Trichinella-specific DNA by polymerase chain reaction (availability limited)
- Trichinella serology
- 2 tests required to ensure accurate diagnosis: first to detect antigen (enzyme-linked immunosorbent assay [ELISA]) and the second to detect antibodies to parasite surface antigens (FA)
- Bentonite flocculation (1:5- or 4-fold increase), latex flocculation test, ELISA, or immunofluorescence
Imaging
- X-ray: may show calcified cysts in muscle (6 " 24 months postinfection) or enlarged heart
- EKG: myocarditis may cause premature contractions, prolonged PR interval, small QRS with intraventricular block, and/or T wave flattening or inversion
- CT: small CNS lesions, IV enhancing ring calcifications
- Electromyography: Results resemble those of polymyositis and inflammatory myopathies.
Diagnostic Procedures/Other
- Skeletal muscle biopsy (especially deltoid or gastrocnemius muscle from the patient at least 17 days after infection)
- Inflammatory cells surround encysted larvae in necrotic muscle fibers.
- Granulomatous reaction present in nonskeletal muscle but not encysted larvae.
- Usually unnecessary, negative result possible in infected patient due to sampling error
- Can test suspected meat if available
Differential Diagnosis
- Infection: viral syndromes, parasitic, spirochete, gastroenteritis, influenza, sinusitis, typhoid fever, measles, scarlet fever, meningitis, rheumatic fever, encephalitis, encephalomyelitis, poliomyelitis, tetanus, schistosomiasis, hookworm, strongyloides, or helminthic infection
- Miscellaneous: fever of unknown origin, dermatomyositis, myocarditis, inflammatory bowel disease, angioneurotic edema, rheumatoid arthritis, glomerulonephritis, polyneuritis, eosinophilic leukemia, polyarteritis nodosa, nonabsorption syndromes
Treatment
Medication
First Line
- Systemic corticosteroids for severe symptoms (not recommended as monotherapy, may prolong adult worm survival in intestines) plus
- Albendazole (Albenza)
- 15 mg/kg/day divided b.i.d for 15 days
- Max dose 800 mg/day
- Teratogenic/embryotoxic in rats
- Approved <2 years
- Mebendazole and albendazole are most efficacious during the enteral phase (active against intestinal worms, little effect on muscle-embedded larvae).
Second Line
Pyrantel pamoate (Antiminth)
- Used during pregnancy; not approved <2 years
- Effective only against adult worms, not encysted larvae
Additional Therapies
General Measures
- Most patients recover without specific therapy.
- Symptomatic treatment: acetaminophen or NSAIDs, bed rest
Issues for Referral
Cardiac, neurologic, pulmonary complications
Inpatient Considerations
Admission Criteria
Cardiac, neurologic, or pulmonary complications indicate more severe disease
Discharge Criteria
Resolution of cardiac symptoms
Ongoing Care
Follow-up Recommendations
- Expect improvement over several weeks.
- At 3 " 4 weeks, retreatment may be indicated if symptoms persist or there are ova in the feces.
Patient Monitoring
Cardiopulmonary monitoring
Diet
- Avoid further exposures.
- Breastfeeding may continue; the single case report of cessation of milk production was associated with parenteral mebendazole.
Patient Education
If concern for trichinosis exposure or symptoms, seek medical care early. Treatment is most efficacious the 1st week after exposure.
Prognosis
- Mild to moderate illness usually resolves spontaneously with minimal sequelae. Muscle swelling and weakness may persist.
- Poorer prognosis (can be fulminant and fatal) with cardiac, CNS, or pulmonary involvement
- Children usually are less symptomatic, have fewer complications, and recover more quickly.
Complications
- Cardiac: myocarditis (may result in death 4 " 8 weeks after infection), secondary arrhythmias, hypotension, pericardial effusion
- Neurologic: meningoencephalitis, CNS granulomas, headaches
- Pulmonary: pneumonia, pneumonitis, pleural effusion, pulmonary embolism or infarct
- Renal: glomerulonephritis
- Hepatic: fatty change
- Muscular: prolonged myalgias
- Ocular: retinal hemorrhages
- Complications rarely are permanent.
Additional Reading
- American Academy of Pediatrics. Trichinellosis. In: Pickering LK, Baker CJ, Kimberlin DW, et al, eds. Red Book: 2012 Report of the Committee on Infectious Diseases. 29th ed. Elk Grove Village, IL: American Academy of Pediatrics. 2012;728 " 729.
- Bruschi F. Trichinellosis in developing countries: is it neglected? J Infect Dev Ctries. 2012;6(3):216 " 222. [View Abstract]
- Gottstein B, Pozio E, Nockler K. Epidemiology, diagnosis, treatment, and control of trichinellosis. Clin Microbiol Rev. 2009;22(1):127 " 145. [View Abstract]
- Ilic N, Gruden-Movsesijan A, Sofronic-Milosavljevic L. Trichinella spiralis: shaping the immune response. Immunol Res. 2012;52(1 " 2):111 " 119. [View Abstract]
- Ozdemir D, Ozkan H, Akkoc N, et al. Acute trichinellosis in children compared with adults. Pediatr Infect Dis J. 2005;24(10):897 " 900. [View Abstract]
- Roy SL, Lopez AS, Schantz PM. Trichinellosis surveillance " United States, 1997 " 2001. MMWR Surveill Summ. 2003;52(6):1 " 8. [View Abstract]
Codes
ICD09
- 124 Trichinosis
- 728.0 Infective myositis
ICD10
- B75 Trichinellosis
- M63.80 Disorders of muscle in diseases classd elswhr, unsp site
SNOMED
- 88264003 Infection by larvae of Trichinella spiralis (disorder)
- 240117006 trichinosis myositis (disorder)
FAQ
- Q: Is trichinosis contagious from person to person?
- A: No, except through infected breast milk.
- Q: Do special precautions need to be taken when treating a patient with presumed trichinosis?
- A: Only thorough hand washing. No isolation required.
- Q: What should we recommend for a patient who has eaten contaminated meat?
- A: Treatment with mebendazole or thiabendazole should be considered.
- Q: What are the classic hallmark signs of trichinosis?
- A: Diarrhea, abdominal pain, periorbital edema, myositis, fever, and eosinophilia, especially when combined with history of ingestion of potentially poorly cooked meat.