Reliability of the enzyme-linked immunosorbent assay (ELISA) for the serodiagnosis of Trichinella spiralis infections in conventionally raised pigs

Abstract

An enzyme immunoassay with horse radish peroxidase as marker enzyme for detection of antibodies to Trichinella spiralis in pigs is described. In the enzyme-linked immunosorbent assay (ELISA) quantitation of specific antibodies is obtained by means of peroxidase labeled anti-species-immunoglobulin in antigen-coated tubes. The enzyme remaining in the tube after washing provides a measure of the amount of specific antibodies in the serum. A crude saline extract of T. spiralis muscle larvae served as antigen, 5 mug protein/ml being a satisfactory concentration. Lyophilization of antigen had no adverse effect on sensitivity. To decrease background staining the use of an optimal conjugate dilution was important. Adding bovine serum albumen to the conjugate was essential to decrease background reactions. Suitable substrate incubation times were studied. Washing was performed with tap water and Tween 20. In experiments with conventionally raised slaughter pigs infected with different numbers of T. spiralis larvae a positive correlation was found between initial dose of larvae and amount of antibodies detected by ELISA. Compared with immunofluorescence (IF) ELISA was more sensitive. IF yielded positive results in 11 out of 34 infected animals, whereas ELISA results were positive in 27. To evaluate ELISA under practical conditions extinction values of sera from infected and non-infected conventional pigs were compared with the highest extinction value in a group of 74 negative conventional pig sera. The relatively high background reaction of some of these negative sera decreased the number of positive practical ELISA results from 27 to 19 out of 34. In 1 out of 10 non-infected animals a false positive practical ELISA result was obtained.