EVALUATION OF AN ENZYME-LINKED-IMMUNOSORBENT-ASSAY AND A HISTAMINE-RELEASE TEST SYSTEM FOR THE DETECTION OF PIGS NATURALLY INFECTED WITH ASCARIS-SUUM

An indirect enzyme-linked immunosorbent assay (ELISA) and a histamine release test system were evaluated for the detection of pigs naturally infected with Ascaris suum. Histamine released by antigen provocation of blood leukocytes was bound selectively to glass microfibres and detected fluorometrically following coupling to o-phthaldialdehyde. Two antigens were used in the two tests: adult body fluid (ABF) and L2/L3 excretory/secretory antigens, obtained by in vitro cultivation of hatched infective larvae. A total of 150 pigs, each weighting approximately 90 kg, from 23 farms were tested. The number of worms in the small intestines of the pigs and the number of eggs in the feces were determined and the liver milkspots counted, together with differential blood leukocyte counts. Seventy one (47%) of the pigs had either adult worms, fecal eggs or liver milkspots. Twenty out of 23 farms (87%) delivered one or more A. suum infected pigs to the slaughterhouse. Liver milkspots were detected in 42.3% of the pigs. When the presence of three or more liver milkspots was considered evidence of an A. suum infection, the ELISA using L2/L3-ES as the antigen gave a test sensitivity of 97% and a specificity of 89%. Significant associations were achieved between the presence of milkspots and the results obtained in the tests using both antigen types in ELISA and using L2/L3 in the histamine release assay: No significant association was found between milkspots and the histamine release test using ABF as antigens, between number of milkspots and presence of intestinal A. suum worms and between the immunological test systems and the hematological data. The ELISA which was employed in this model could be of value in epidemiological surveys as well as in combination with surveillance of other infections in pigs, in which blood sampling is regularly performed. Furthermore, the ELISA may be used as a tool to classify herds as A. suum free.