Comparison of serological methods for the diagnosis of Neospora caninum infection in cattle

Authors: WAPENAAR, W - ATLANTIC VET COLLEGE; BARKEMA, H - ATLANTIC VET COLLEGE; VAN LEEUWEN, J - ATLANTIC VET COLLEGE; MC CLURE, J - ATLANTIC VET COLLEGE; O'HANDLEY, R - MURDOCH UNIV, W AUSTRALIA; Kwok, Oliver; THULLIEZ, P - INST. DE PUERICULTURE; Dubey, Jitender; Jenkins, Mark

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2006
Publication Date: 1/5/2007
Citation: Wapenaar, W., Barkema, H.W., Van Leeuwen, J.A., Mc Clure, J.T., O'Handley, R.M., Kwok, O.C., Thulliez, P., Dubey, J.P., Jenkins, M.C. 2007. Comparison of serological methods for the diagnosis of Neospora caninum infection in cattle. Veterinary Parasitology. 143:166-173.

Interpretive Summary: Bovine neosporosis is a reproductive disease of cattle caused by the protozoan parasite Neospora caninum. The disease is a major cause of abortion in dairy cattle worldwide. Although several groups are developing a vaccine against this disease, another method of control is to prevent exposure of cows to the parasite stage that is shed by dogs and coyotes. The purpose of the present study was to compare different serological tests for N. caninum infection with the goal of deciding which assay best identified infected cows. The study showed that most commercial ELISA tests are as good as the standard assay based on immunofluorescence staining. This research should help epidemiologists evaluate the true infection status of dairy herds.

Technical Abstract: The aims of this study were to evaluate the performance and agreement of various commercial and in-house Neospora caninum antibody assays used in dairy cattle in North America, and to investigate reproducibility of two assays performed in different laboratories. Three enzyme linked immunosorbent assays (ELISAs; a competitive ELISA - VMRD Inc., an indirect ELISA - Biovet Inc., and another indirect ELISA - Herdchek IDEXX Corp.), 2 indirect fluorescent antibody tests (IFATs; VMRD Inc., and in-house USDA) and 1 N. caninum agglutination test (NAT, in-house USDA) were utilized to test 397 randomly selected dairy cattle serum samples from 34 herds in eastern Canada for antibodies to N. caninum. The manufacturers’ recommended cut-off values were used to evaluate test performance and agreement between tests. One IFAT (VMRD Inc.) performed well (sensitivity and specificity: 0.97 and 0.97) using reference sera (n=452), therefore results from this IFAT on the 397 samples could subsequently be used as reference standard to calculate test characteristics for the other assays. Only 11% of the 397 sera were found to be N. caninum-positive with the IFAT. Prevalence-adjusted bias-adjusted kappa (PABAK) ranged from 0.06 to 0.99. Positive agreement was moderate to very good (Ppos = 0.25 to 0.96). Negative agreement was very good for all assays (Pneg>0.94) except NAT (Pneg=0.66). Sensitivity was '0.89 for all assays except the NAT which had a significantly lower sensitivity (0.66). Specificity was high (>0.94) for all assays except for one indirect ELISA (specificity=0.52). The performance characteristics observed for most assays in this study make them useful for screening antibodies to N. caninum in cattle.