FIELD-EVALUATION OF THE ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR SWINE TRICHINOSIS - EFFICACY OF THE EXCRETORY-SECRETORY ANTIGEN

  • 1 May 1986
    • journal article
    • research article
    • Vol. 47  (5) , 1046-1049
Abstract
A field evaluation of an enzyme-linked immunosorbent assay (ELISA) for swine trichinosis was done with sera obtained from 5 herds experiencing ongoing transmission of Trichinella spiralis. Epizootiologic studies conducted on these herds offered an opportunity to evaluate the accuracy of an ELISA, using larval T. spiralis excretory-secretory antigens. Sera from 162 infected pigs and 143 serum samples from noninfected pigs originating from the same farms were tested. The infection status of the pigs was determined by digestion of diaphragm or tongue muscle samples. Two criteria were established to classify the ELISA optical density (OD) readings: Criterion I stated that an OD .gtoreq. 5 times the mean OD of several normal swine sera pools was positive; criterion II stated that a OD .gtoreq. 4 times the normal sera values was positive. The results obtained did not reveal obvious serologic variations among infected herds located in the 4 states involved. Overall, the test detected 93% (criterion I) and 96% (criterion II) of infected pigs. The majority of false-negative sera was from hogs that had < 5 larvae/g of muscle; 1 hog and 73.8 larvae/g of diaphragm muscle. The false-positive rates were 8% for criterion I and 9% for criterion II. The actual rate for these false-positive samples may have been overestimated, because generally, only small tissue samples (0.4 to 10 g) were digested; larger sample sizes might have altered the results. The relevance of this qualification is that these pigs originated from herds with prevalence rates > 50%. Other factors that may account for occasional false-positive sera or false-negative sera in the swine trichinosis ELISA are discussed. Finally, the liabilities and assets of this serologic test are considered in relation to its application for herd screening and its use as an antemortem test.