Expression of recombinant dense granule protein 7 of Neospora caninum and evaluation of its diagnostic potential for canine neosporosis

Neospora caninum infection is an important disease affecting bovine and canine populations worldwide. The dense granule antigen 7 of N. caninum (NcGRA7) is considered to be an immunodominant antigen. In the present study, the gene encoding truncated NcGRA7 (NcGRA7t) lacking an N-terminal signal peptide was expressed in Escherichia coli, and its diagnostic potential in an enzyme-linked immunosorbent assay (ELISA) was evaluated. The ELISA could clearly discriminate between known N. caninum-positive and -negative sera from dogs. Serum samples randomly collected from dogs in Japan and China were examined for the diagnosis of neosporosis using the ELISA. Twenty-three of 135 samples (17.03%) and 9 of 95 (9.47%) samples from Japan and China, respectively, were positive for antibodies to N. caninum. Of the 32 ELISA-positive samples, 29 (90.62%) were confirmed as positive by Western blot analysis with whole tachyzoite antigens. These results indicate that the recombinant NcGRA7t would be a reliable antigen in ELISA for the diagnosis of canine neosporosis.