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Clinical and Diagnostic Laboratory Immunology, May 2002, p. 611-615, Vol. 9, No. 3
1071-412X/02/$04.00+0     DOI: 10.1128/CDLI.9.3.611-615.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Sensitive and Specific Identification of Neospora caninum Infection of Cattle Based on Detection of Serum Antibodies to Recombinant Ncp29

Daniel K. Howe,^1, Keliang Tang,¹ Patricia A. Conrad,² Karen Sverlow,^3, J. P. Dubey,⁴ and L. David Sibley^1*

Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri 63110,¹ Department of Pathology, Microbiology, and Immunology, School of Veterinary Medicine,² California Veterinary Diagnostic Laboratory System, University of California, Davis, Davis, California 95616,³ Parasite Biology, Epidemiology, and Systematics Laboratory, USDA Agricultural Research Service, Animal and Natural Resources Institute, Beltsville, Maryland 20705⁴

Received 9 October 2001/ Returned for modification 30 November 2001/ Accepted 22 January 2002

Neosporosis is an economically important disease of dairy cattle caused by the protozoan Neospora caninum. Diagnostic tests for neosporosis are complicated by the potential for cross-reaction of antibodies to antigens that are similar between N. caninum and closely related parasites Toxoplasma gondii and Sarcocystis cruzi. To provide a sensitive and specific assay for detecting antibodies to N. caninum in the serum of infected animals, we have investigated a recombinant form of the antigen known as Ncp29 (rNcp29), which is a major surface protein of the parasite. Ncp29 is encoded by a gene that is homologous to the SAG1 gene previously characterized from T. gondii. An enzyme-linked immunosorbent assay (ELISA) was used to screen animals for the presence of serum antibodies specific to rNcp29. The rNcp29 ELISA readily distinguished between cattle known to be infected with N. caninum (optical density [OD] > 1.2 at 1:500 or greater dilution) and negative controls (OD < 0.5 at 1:500). Additionally, sera from animals that were infected with T. gondii or S. cruzi were negative. The rNcp29 ELISA developed here provides a specific and sensitive assay for detecting neosporosis in cattle.

Present address: Gluck Equine Research Center, Department of Veterinary Sciences, University of Kentucky Lexington, KY 40546-0099.

Present address: Heska Corporation, Ft. Collins, CO 80525.

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