Enzyme immunoassay for swine trichinellosis using antigens purified by immunoaffinity chromatography

Various preparations of crude and a purified preparation of Trichinella spiralis antigens were compared in a rapid, micro-enzyme immunoassay (EIA) for detecting trichinellosis in swine. The crude antigen preparations (XM-300 or S3 fraction) were lipid-free, cell-free fractions of muscle larvae, and the purified antigen was prepared by immunoaffinity chromatography of the soluble fraction of stichocyte secretory granules from rat muscle larvae. The antigens were tested against normal and immune swine sera for sensitivity and specificity, and for their ability to detect seroconversions early in the immune response. At optimum concentrations, absorbance values from immune and nonimmune sera produced sample to noise (S/N) ratios three-fold higher for the column antigen than for XM-300. Tests of sequential sera from experimentally-infected pigs showed that the column antigen produced lower absorbances with pre-infection sera and, from 18 days post-infection, higher absorbances with positive sera. From 21-28 days post-infection, absorbances and S/N ratios with column antigen were nearly twice those with XM-300. Column antigen detected antibodies more often than XM-300 antigen in sera collected prior to the appearance of larvae. Crude antigen did not distinguish all true negatives from weakly positives in a study involving 100 sera from muscle digestion-negative pigs and 75 sera from experimentally infected pigs, whereas the column antigen distinguished all negatives from positives. In a larger scale test of the column antigen, 1,130 pigs from Puerto Rico were tested in the micro-EIA test. Puerto Rico has no endogenous trichinellosis, and all 1,130 pigs were shown to be muscle digestion negative. These same pigs were all negative using the column antigen. These results show that the column antigen out-performs the crude antigens in sensitivity, specificity, and early detection. The column antigen is therefore a major improvement in the EIA for swine trichinellosis.