Rare detection of Neospora caninum in placentas from seropositive dams giving birth to full-term calves

Neospora caninum is thought to be transmitted to cattle by dogs, the only k nown definitive host. Although aborted fetuses seem the most likely source of infective material for dogs, placentas from seropositive dams appear als o as a potential source of infective material. The objective of the study w as to evaluate the presence of N. caninum organisms in placentas of full-te rm calves born to seropositive cows. Sixteen placentas, 11 from Neospora-se ropositive cows, were examined histologically and by immunohistochemistry a nd polymerase chain reaction (PCR) assay for the presence of N. caninum. Mi ld placentitis was observed in all placentas. Neospora caninum was not iden tified by immunohistochemistry, but placentas from 2 seropositive dams were positive for N. caninum by PCR. These results suggest that placentas of fu ll-term calves from seropositive cows may be a potential source of N. canin um for dogs, but the incidence of this mode of transmission is likely to be low.