Pathogenic characterization in mice of Neospora caninum isolates obtained from asymptomatic calves.

In this study, we characterized 8 new isolates obtained from healthy but congenitally infected calves using a BALB/c mouse model. Neospora caninum-infected mice survived without exhibiting any clinical signs of disease. Nevertheless, differences among isolates in parasite organ distribution, parasite burden and the severity of histopathological lesions were determined. Mice infected with the Nc-Spain 5H, Nc-Spain 7 and Nc-Spain 9 isolates showed higher parasite burdens and more severe brain lesions during the late phase of infection compared to mice infected with the Nc-Spain 2H, Nc-Spain 3H or Nc-Spain 6 isolates. Furthermore, differences in the immunoglobulin IgG1 and IgG2a isotype kinetics induced by these isolates were observed, with a more rapid IgG2a response seen in mice infected with the Nc-Spain 2H and Nc-Spain 3H isolates. These results confirm the intra-species variability of N. caninum pathogenicity.