A MULTIPLE ANTIGEN ELISA TO DETECT NEOSPORA-SPECIFIC ANTIBODIES IN BOVINE SERA, BOVINE FETAL FLUIDS, OVINE AND CAPRINE SERA

Neospora caninum is a cyst-forming coccidian parasite recently identif ied as a cause of abortion in cattle. The epidemiology of neosporosis is poorly understood, partly because accurate diagnosis of infection i s difficult. In this paper we describe the development of a multiple a ntigen-based enzyme-linked immunosorbent assay (ELISA) to detect antib odies to N. caninum in sera from cable, sheep and goats as well as fro m bovine foetal fluids. A water-soluble fraction (wsf) of sonicated NC -1 strain tachyzoites was used as the antigen in the ELISA. Minimum op tical density (OD) values that were considered to be Neospora antibody -positive, that is, the cut-off OD values were determined separately f or bovine maternal sera, bovine foetal fluids, ovine sera and caprine sera; they were 0.40, 0.17, 0.23 and 0.41 OD, respectively. The ELISA gave a high signal/noise ratio, giving good sensitivity and specificit y, correlating well with the indirect fluorescent antibody test (IFAT) currently used to diagnose Neospora infection in cattle, sheep and go ats. In both the ELISA and immunoblot analysis using the same antigen, there was no significant cross-reactivity with sera from cattle, shee p or goats that had been infected with Toxoplasma gondii. The ELISA al so showed no cross-reactivity in sera from cattle infected with Sarcoc ystis cruzi, Babesia divergens, B. bovis and B. bigemina. The wsf frac tion of sonicated N. caninum tachyzoites used in this ELISA can be eas ily prepared and may be more sensitive than a single antigen ELISA, wh ilst still retaining good specificity. (C) 1998 Elsevier Science B.V. All rights reserved.