Serum antibody response to soluble extract of the third-larval stage of Ostertagia ostertagi in cattle.

Serum IgG, IgM, and IgA antibody responses against L3 antigens of Ostertagia ostertagi were monitored by enzyme-linked immunosorbent assay (ELISA) after one, two or multiple sequential inoculations of this nematode in calves. Following the first infection, antibody levels did not change. After a second inoculation, IgG increased significantly (P less than 0.05) after 2 months. IgG was not significantly increased 1 month after challenge inoculation. IgM and IgA antibody levels did not change following the first or second inoculations of L3. IgG antibody levels rose only slightly following multiple sequential inoculations with infectious L3. Results indicate that calves with ostertagiasis have very weak serum antibody responses to L3, and these appear to be of little value in detection of the infection in these animals.