ORAL NEOSPORA-CANINUM INOCULATION OF NEONATAL CALVES

Four calves born to cows seronegative for Neospora caninum were dosed orally within 6h after birth with tachyzoites of the bovine N. caninum Nc-SweB1 isolate added to colostrum. Two of the calves were dosed via stomach tube and two by feeding bottle. The latter two calves showed transient fever and passed blood-stained diarrhoea 1-2 weeks after ino culation. From 5 weeks after inoculation they developed a significant antibody response which remained high until the calves were euthanised and necropsied at 15 and 19 weeks after inoculation, respectively. Th e two calves inocula ted by stomach tube showed no clinical signs and they remained seronegative throughout the study. At necropsy of the se ropositive calves, no pathological lesions were seen, and parasites we re not detected by immunohistochemistry. Neospora caninum was not re-i solated in cell culture from the brains of the seropositive calves; ho wever, N. caninum DNA was detected in brain from both of them by PCR. The data suggest that oral infection of N, caninum via colostrum might be a possible route of vertical transmission in newborn calves, in ad dition to transplacental infection. (C) 1998 Australian Society for Pa rasitology. Published by Elsevier Science Ltd. All rights reserved.