Recent reports indicate N. caninum has a possible role in causing abortions in sheep in New Zealand. Knowledge about the mode of transmission of neosporosis in sheep in New Zealand is limited. This study aimed to determine the rate of vertical transmission that would occur in lambs born from experimentally inoculated ewes and to determine if previous inoculation would protect the lambs from N. caninum infection. A group of 50 ewes was divided into 2 groups with one group being inoculated with 5×10(6) N. caninum tachyzoites prior to pregnancy in Year 1. In Year 2, each of these groups was subdivided into 2 groups with one from each original group being inoculated with 1×10(7) N. caninum tachyzoites on Day 120 of gestation. Inoculation of N. caninum tachyzoites into ewes prior to mating resulted in no congenital transmission in lambs born in Year 1 but without further inoculation, 7 out of 11 lambs in Year 2 were positive for N. caninum infection. Ewes that were inoculated in both years resulted in all 12 lambs born in Year 2 being positive for N. caninum infection. This indicates that previous inoculation in Year 1 did not result in any vertical transmission in that year but did not provide any protection against vertical transmission in Year 2. These results suggest that vertical transmission occurs readily once the ewe is infected.
To determine if toltrazuril was effective in eliminating Neospora caninum infection from congenitally infected lambs. Twenty-eight ewes were allocated to 3 groups where animals in Groups A and B were inoculated with 1 × 10(7)N. caninum tachyzoites on Day 120 of gestation and Group C was maintained as a negative control group. Lambs born from ewes in Group A were treated with toltrazuril (20mg/kg) on Days 0, 7, 14 and 21 after birth. Lambs in Groups B and C were untreated. All lambs in Groups A and B were seropositive at 12 weeks of age. At 12 weeks of age, no differences between lambs in Group A and Group B were observed in serological results (ELISA and western blot), presence of N. caninum-related brain histopathological lesions or the number of organisms detected by qPCR. Group C remained negative for serology, detection of N. caninum DNA as well as histopathology throughout the study. Results indicate that N. caninum congenitally-infected lambs had a continuing infection with N. caninum despite being treated with toltrazuril.