Evaluation of Neospora caninum truncated dense granule protein 2 for serodiagnosis by enzyme-linked immunosorbent assay in dogs.

Neosporosis is an infectious disease caused by Neospora caninum, and it primarily affects cattle and dogs. An infection by N. caninum causes fetal abortion and neonatal mortality. Previous proteomics and immunoscreening analyses revealed that N. caninum dense granule antigen 2 (NcGRA2) has potential for serodiagnosis of N. caninum. Consequently, we expressed the truncated NcGRA2 (NcGRA2t), which lacks a signal peptide. We compared the serodiagnostic performances of recombinant NcGRA2t with that of truncated surface antigen 1 of N. caninum (NcSAG1t). Specificity testing using sera from mice infected with Toxoplasma gondii indicated that the NcGRA2t recombinant protein does not cross-react with T. gondii. In addition, we detected anti-NcGRA2t antibody at the acute stage in experimentally infected dogs, while detecting anti-NcSAG1t antibody during both the acute and chronic stages. Our results suggest that the levels of anti-NcGRA2 antibody reflect parasite activation in dogs. In conclusion, antibodies against NcGRA2t and NcSAG1t are suitable indicators to distinguish the acute and chronic stages of N. caninum infection.