Fetal loss in BALB/C mice infected with Neospora caninum.

The suitability of mice as a model for reproductive loss due to Neospora caninum infection was investigated. Groups of mice were infected with 2 x 10(6) N. caninum before pregnancy (10 days) and during pregnancy (days 5 and 10 of gestation). In mice infected before and during early pregnancy, fetal loss was evaluated throughout gestation, and pregnancy loss was evaluated by enumeration of fetal resorptions and total fetuses. In mice infected before pregnancy, no difference was present in resorptions between infected and control mice, although litter size was decreased in the infected mice (P < 0.05). In mice infected during early pregnancy (day 5 gestation) and examined temporally throughout gestation, resorptions were increased in the infected mice compared to the control mice (P < 0.05). In mice infected at 5 days gestation and examined at one time point (day 14 of gestation), the resorption rate for infected mice was 33% and 12% for controls (P < 0.05). Routine histopathologic examination and immunohistochemistry using N. caninum-specific antisera did not identify tachyzoites in placental and fetal tissues during the pre- and early pregnancy infections. In mice infected late midgestation (day 10), N. caninum tachyzoites were identified in placenta and fetal muscle and neural tissue. In the placenta, there was multifocal necrosis and hemorrhage with intralesional tachyzoites. Tachyzoites in fetal tissues were not associated with pathologic changes. No reproductive loss was associated with mice infected late in gestation. These data demonstrate that mice can be used as a model for the study of fetal resorption and congenital infection associated with N. caninum.