Experimental studies on the transmission of Neospora caninum between cattle

Three studies were conducted to investigate the transmission of Neospora caninum between cattle by the oral route. In the first study, six calves were dosed with 10(7) N caninum tachyzoites (Ne LivB1) in colostrum and/or milk replacer on four occasions. In the second study, two calves and two cows were fed placental tissues from N caninum-infected cows, and, in the third study, seven uninfected calves were fostered onto N caninum-infected dams. In the first study, all six calves developed antibody responses and five calves developed antigen-specific lymphoproliferation responses, including two calves initially challenged at 1 week of age. No evidence of N caninum infection was found in the brain or heart of these calves by histology or polymerase chain reaction (PCR). In the second and third studies, there was no evidence of N caninum infection in any of the calves and cows. The results confirm that calves up to 1 week of age can be experimentally infected via the oral route, but suggest that this is not an important natural route of transmission for N caninum between cattle. (C) 2001 Harcourt Publishers Ltd.