The phylogenetic relationships amongst Hammondia, Neospora and Toxoplasma were investigated by DNA sequence comparisons of the D2/D3 domain of the large subunit ribosomal DNA and the internal transcribed spacer 1. The results obtained allow us to reject the hypothesis that N. caninum and H. heydorni are the same species and show that Hammondia hammondi is probably the sister taxon to Toxoplasma gondii.

This study compared the biological and genetic properties of a bovine (NC-SweB1) and a canine (NC-Liverpool) isolate of Neospora caninum. A mouse model for CNS infection demonstrated marked differences in pathogenicity between the isolates. NC-Liverpool induced severe clinical signs of neosporosis in 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 time-period. Statistically significant differences were observed between the isolates in the response (mean weight loss) of mice through time to the different doses inoculated. Histopathological effects on brain tissue reflected the isolate-based differences described above. NC-Liverpool infection resulted in intense inflammatory infiltrates and highly necrotic lesions whereas NC-SweB1 induced a milder meningoencephalitis. Passage in cell-culture over 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 DNA from NC-SweB1 or Toxoplasma gondii. In summary this study provides evidence for significant biological and genetic differences between 2 isolates of N. caninum.

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Fetal loss and vertical transmission of Neospora caninum were evaluated in outbred Quackenbush (Qs) mice with respect to dose of parasites, N. caninum isolate, and route of injection. Mice were infected with NC-Liverpool or NC-SweB1 at day 5 or 8 of pregnancy with doses of 10(4), 10(6), or 10(7) parasites, through either a subcutaneous or intraperitoneal injection. Polymerase chain reaction was used to detect N. caninum in the brains of offspring, and enzyme-linked immunosorbent assay was used to analyze the maternal immune response. Vertical transmission occurred in mice given 10(6) NC-Liverpool at day 5 during gestation, and a significant (P < 0.05) maternal antibody response was observed in mice infected with NC-Liverpool or NC-SweB1 at days 5 and 8 of gestation. This study shows that outbred Qs mice are a useful model for the study of vertical transmission associated with N. caninum, as they display less clinical disease and pathogenesis than inbred mice and have large litters, which is advantageous when studying maternal transmission.