Protection against vertical transmission in bovine neosporosis

In this study we were interested to determine whether infection of cattle p rior to pregnancy would afford any protection to the foetus if the dams wer e challenged with Neospora caninum at mid-gestation. The experiment compris ed four groups, of cattle: group 1. uninfected controls; group 2, inoculate d with N. caninum tachyzoites 6 weeks prior to mating and then challenged w ith N. caninum at mid-gestation; group 3. naive cattle challenged with N. c aninum at mid-gestation and group 4 were infected with N. caninum prior to mating and left unchallenged throughout pregnancy. Positive cell-mediated a nd humoral immune responses to N. caninum were recorded in groups 2 and 4 p rior to pregnancy and in groups 2, 3 and 4 following challenge at mid-gesta tion. However there was a marked down regulation of the cell-mediated immun e response in all groups around mid-gestation. There was a significant incr ease in rectal temperature response in animals in group 3 compared to group 2 following challenge but no other clinical symptoms of disease were recor ded and all cattle proceeded to calving. At calving, pre-colostral blood sa mples were negative for antibodies to N. caninum in all the calves born to dams in groups 1, 2 and 4. In contrast, all the calves born to dams in grou p 3 had high levels of specific antibody to N. caninum indicating that they had been exposed to the parasite in utero. At post-mortem N. caninum DNA w as detected in CNS. thymus and placental cotyledon samples in calves from g roup 3. All tissue samples from calves in the other 3 groups were negative for V. caninum DNA with the exception of one calf from group 2 where specif ic DNA was detected in a sample of spinal cord. These results suggest that the immune response generated in the dams in group 2 prior to pregnancy had protected against vertical transmission of the parasite following challeng e at mid-gestation. (C) 2001 Australian Society for Parasitology Inc. Publi shed by Elsevier Science Ltd. All rights reserved.