Diagnostic tests for Trichinella spiralis infection in pigs. A comparative study of ELISA for specific antibody and histamine release from blood cells in experimental infections.

A study on the histamine release test (HR) for the demonstration of infections with Trichinella spiralis in pigs was carried out on 18 pigs, six infected with 200 larvae, six infected with 5000 larvae and six non-infected (control group). The results obtained by HR during a 7 week infection were compared with those of the enzyme-linked immunosorbent assay (ELISA). All inoculated pigs were found to be positive on Day 40 post-inoculation (p.i.) by necropsy examination of selected muscle groups, with mean recoveries of 7.9 and 225 larvae g-1 of tissue in the low- and high-dose group, respectively. At this time, all animals of the high-dose group and five out of six animals of the low-dose group were antibody positive in ELISA with any of three coating antigens employed (a crude muscle larva extract, an excretory/secretory (ES) antigen and a purified 45 kDa antigen). HR performed on whole blood was positive in four out of six pigs of the high-dose group and one out of six pigs of the low-dose group. The earliest ELISA seroconversions took place at Day 15 p.i. with crude and ES antigens. The earliest measurable reaction in HR performed on whole blood was found on Day 19 p.i. There was considerable individual variation regarding which test was the most sensitive for the early detection of infection. Washing of the blood cells prior to antigen provocation led to a markedly improved sensitivity of HR, all animals of the high-dose and three out of six animals of the low-dose group being positive by Day 40 p.i. The time course of the development of ELISA titres and HR reactivity indicated that this effect is due to the removal of blocking antibodies.