Trichinellosis/Trichinosis Workup

Updated: Nov 06, 2015
  • Author: L Kristian Arnold, MD, MPH; Chief Editor: Jeter (Jay) Pritchard Taylor, III, MD  more...
  • Print
Workup

Laboratory Studies

There is no definitive laboratory test with easy availability to the emergency physician.

CBC reveals eosinophilia in virtually all patients, though it does not develop until 2-6 weeks following ingestion of infected meat when larvae pass out of the intestines. Of note, eosinopenia has been noted to be associated with more severe infections and an early fall in eosinophils with a poorer outcomes. [62] Eosinophilia may persist for up to 3 months.

Creatine phosphokinase and lactic dehydrogenase levels are elevated in 90% of patients once the muscle invasion phase begins.

Urinalysis (UA) may reveal myoglobinuria.

Parasite-specific indirect immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) titers (100%) and anti-newborn larvae antibodies (30%) begin to be positive within 2 weeks of infection. These may not be positive initially, and they also are subject to some cross-reactivity with other parasitic disorders making their specificity less when weakly positive. [63] Western-blot analysis is used as a confirmatory evaluation. [64]

Next:

Imaging Studies

Plain radiographs of the extremities

Calcified densities in the muscles, indicating an old trichinization, may be the only positive radiographic findings.

Radiographs do not help evaluate acute infestation.

Computerized tomographic (CT) scanning of the brain

CT scanning may be helpful in patients demonstrating neurologic symptoms.

CT scan reveals focal deficits with small hypodensities in the cortex and white matter. [12]

Abnormal findings are unlikely in patients without neurologic symptoms.

CT scanning of the orbits is warranted in patients with chemosis to rule out other causes of proptosis. [58]

Magnetic resonance imaging (MRI) of the brain

Diffusion-weighted MRI may be helpful in defining lesions noted on plain MRI. [65]

Previous
Next:

Other Tests

ECG may show signs of ischemia, pericarditis, or myocarditis, such as the following [66] :

  • Premature atrial or ventricular contractions
  • P-R prolongation
  • Flattened or inverted T waves
  • Conduction blocks
  • Atrial fibrillation

Cardiac ultrasound (ECHO) may demonstrate pericardial fluid or wall motion abnormalities. [66]

Previous
Next:

Procedures

A muscle biopsy is the definitive diagnostic test but is not an ED procedure. It is also being replaced for treatment decisions by algorithms such as one presented below. Consider the following when performing biopsy:

  • Larvae are found free or encapsulated, depending on the species of Trichinella causing the infection.
  • At the time of biopsy, initial preparation may be made by crushing a portion of muscle tissue between 2 slides and viewing directly.
  • Biopsy may be negative in active infection due to physically missing an area of implantation if the number of larvae in muscle tissue is low enough that the biopsy misses an infected area.
  • Treatment should not be withheld in the face of a negative biopsy result and negative immunoglobulins if there is high clinical suspicion. [67]
  • Polymerase chain reaction (PCR) evaluation of biopsy tissue for Trichinella -specific DNA, because of the high sensitivity and specificity, may detect the presence of worms in cases where initial biopsy results are negative. See the image below.
    Photomicrograph depicting numbers of Trichinella s Photomicrograph depicting numbers of Trichinella spiralis cysts seen embedded in a muscle tissue specimen, in a case of trichinellosis. Image courtesy of the Centers for Disease Control and Prevention.

The Food and Agriculture Organization of the United Nations (FAO), in conjunction with the WHO and the World Organization for Animal Health (OIE), have proposed an algorithm for predicting the likelihood of being infected with Trichinella based on combinations of clinical and laboratory elements and their relative sensitivities and specificities. [4] Diagnosis of confirmed cases requires fever, facial/eyelid edema, and myalgia, along with a positive high-specificity serologic test result, seroconversion, or a positive muscle biopsy finding. Alternatively, diagnosis is confirmed with eosinophilia, elevated IgE levels, or elevated muscle enzymes; a positive high-specificity serologic test result, seroconversion, or a positive muscle biopsy finding; and at least one of the following:

  • Fever
  • Myalgia
  • Facial/eyelid edema
  • Neurological signs
  • Cardiological signs
  • Conjunctivitis
  • Subungual hemorrhages
  • Cutaneous rash

This algorithm allows for graded suspicion based on various combinations and does not always require serology or muscle biopsy. For example, high probability cases are defined by the presence of myalgia, eyelid/facial edema, and fever and at least 2 of the following:

  • Eosinophilia
  • Elevated IgE level
  • Elevated muscle enzyme level
Previous