Comparison of the biological characteristics of two isolates of Neospora caninum

This study compared the biological and genetic properties of a bovine (NC-S weB1) and a canine (NC-Liverpool) isolate of Neospora caninum. A mouse mode l for CNS infection demonstrated marked differences in pathogenicity betwee n the isolates. NC-Liverpool induced severe clinical signs of neosporosis i n 57/58 mice including discoordinated movement, hindlimb paralysis and coat ruffling with severe weight loss. In contrast NC-SweB1 induced similar but less severe symptoms in a much smaller proportion of mice over the same ti me-period. Statistically significant differences were observed between the isolates in the response (mean weight loss) of mice through time to the dif ferent doses inoculated. Histopathological effects on brain tissue reflecte d the isolate-based differences described above. NC-Liverpool infection res ulted in intense inflammatory infiltrates and highly necrotic lesions where as NC-SweB1 induced a milder meningoencephalitis. Passage in cell-culture o ver a period of 14 months did not affect the pathogenicity of NC-liverpool. Immunoblots showed that antibodies to N. caninum appeared earlier in mice inoculated with NC-Liverpool than with NC-SweB1. Finally, RAPD-PCR analysis of NC-Liverpool DNA generated profiles distinct from that observed with DN A from NC-SweB1 or Toxoplasma gondii. In summary this study provides eviden ce for significant biological and genetic differences between 2 isolates N. caninum.