EVALUATION OF 2 NEOSPORA-CANINUM RECOMBINANT ANTIGENS FOR USE IN AN ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR THE DIAGNOSIS OF BOVINE NEOSPOROSIS

Neospora caninum is a recently described apicomplexan parasite which c auses paralysis and death in dogs. Neospora parasites also cause abort ion and neonatal morbidity in cattle, sheep, goats, and horses, and ne osporosis is emerging as an important cause of bovine abortion worldwi de. The purpose of this study was to identify N. caninum cDNA clones e ncoding antigens that would be useful for the immunodiagnosis of bovin e neosporosis. Two N. caninum tachyzoite cDNA clones expressing antige ns that were recognized by serum from naturally and experimentally inf ected cattle were identified. The DNA sequences of these clones were d etermined, and the inserts were subcloned into the plasmid expression vector pTrcHisB. Both recombinant antigens, expressed as fusion protei ns with a His(6) tag, were purified on a nickel-chelating affinity col umn and evaluated in separate enzyme-linked immunosorbent assays (ELIS As). Both recombinant antigen ELISAs were capable of distinguishing be tween sera from Neospora-infected cows and sera from uninfected contro l cows. Furthermore, both assays were able to detect an antibody respo nse in animals that were experimentally inoculated with N caninum. Nei ther antigen showed evidence of cross-reactivity with serum from anima ls inoculated with the closely related parasites Toxoplasma gondii, Sa rcocystis cruzi, Sarcocystis hominis, and Sarcocystis hirsuta.