Diagnosis of swine trichinosis by enzyme-linked immunosorbent assay (ELISA) using an excretory--secretory antigen.

An excretory--secretory (ES) antigen was used in a serodiagnostic enzyme-linke immunosorbent assay (ELISA) for swine trichinosis. ELISA procedures included a double-antibody test, using either an anti-swine IgG or a protein A enzyme conjugate, and a triple-antibody test using a pig IgG heavy-chain specific second antibody with a conjugated third antibody. The ES antigen was effective in eliminating all false-positive reactivity in sera from farm-raised hogs. The triple-antibody procedure was more sensitive and demonstrated a greater efficiency in detecting positive animals and early seroconversions. Naturally-infected pigs with worm burdens as low as 0.01 larvae per gram (LPG) of diaphragm were seropositive using these procedures. Seroconversion in experimentally-infected animals receiving low doses of muscle larvae (500) occurred considerably later than in animals receiving high doses (10000). This might account for false-negative reactions in naturally-infected animals with very low (less than 0.1 LPG) worm burdens.