Antibody Detection
Immunodiagnostic tests currently available in the U.S. include enzyme immunoassays (EIA).  Antigen preparations may be crude antigens prepared from homogenates of Trichinella spiralis muscle larvae or excretory-secretory (ES) products produced by cultured larvae.  The TSL-1 group of larval secretory antigens are conserved in all species/isolates of Trichinella and thus can be used to detect infection in animals or people infected with any of the types of Trichinella currently recognized.  Positive reactions are detectable at some time during infection in serum samples of 80% to 100% of patients with clinically symptomatic trichinellosis (trichinosis).  Antibody levels are often not detectable until 3 to 5 weeks postinfection, well after the onset of acute-stage illness.  Antibody development is also affected by the infecting dose of larvae: the higher the infecting dose, the faster the patient's antibody response will develop.  Multiple serum specimens should be drawn several weeks apart to demonstrate seroconversion in patients whose initial specimen was negative.  IgG, IgM, and IgE antibodies are detectable in many patients; however, tests based on IgG antibodies are most sensitive.  Antibody levels peak in the second or third month postinfection and then decline slowly for several years.
In our experience at CDC, EIA with ES antigen detects antibodies earlier than BF in 25% of serum specimens from patients with acute infection, but the EIA also remains positive for longer periods after infection than the BF, and is reactive in a larger proportion of persons with no clinical evidence of trichinellosis.  One commercial EIA kit is available in the United States.

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